12dB of noise reduction by a NOLM based 2-R regenerator - Schmauß, Bernhard; Rösch, Matthias; et al. (IEEE Photonics Technology Letters, 2003)
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.optik.1optik.12dbof

12 dB of Noise Reduction by a NOLM based all optical all passive Regenerator - Meißner, Markus; Rösch, Matthias; Schmauß, Bernhard; Leuchs, Gerd (CLEO Europe, June, 2003)
UnivIS-Import:2015-04-16:Pub.2003.tech.IE.LEH.12dbof_5

2D Carbon Allotrope with Incorporated Au-Ag Nanoclusters - Laser-Induced Synthesis and Optical Characterization - Manshina, Alina; Petrov, Yuriy; Kolesnikov, I.; Mitetelo, N. V.; Murzina, T. V.; Butt, M. A.; Neugebauer, M.; Banzer, Peter; Leuchs, Gerd (2018 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2018, 2019)
We discuss the laser-induced fabrication and detailed structural and optical characterization of a novel carbon allotrope intercalated with bimetallic nanoclusters.
CRIS-Team Scopus Importer:2019-05-21

2R-Regeneration of an 80-Gb/s RZ-DQPSK signal by a nonlinear amplifying loop mirror - Cvecek, Kristian; Sponsel, Klaus; Ludwig, R.; Schubert, C.; Stephan, Christian; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (IEEE Photonics Technology Letters, 2007)
The performance of a nonlinear amplifying loop mirror as a 2R-regenerator for an 80-Gb/s return-to-zero differential-quadrature-phase-shift-keyed signal has been investigated experimentally. A significant eye-opening improvement and a negative power penalty of up to 2.6 dB were obtained. © 2007 IEEE.
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.optik.1optik.2rrege
Keywords: 2R-regeneration; All-optical regeneration; Differential quadrature phase-shift keying (DQPSK); Nonlinear amplifying loop mirror (NALM)

2R-Regeneration of an RZ-DPSK Signal Using a Nonlinear Amplifying Loop Mirror - Cvecek, K; Sponsel, K; Onishchukov, G; Schmauß, Bernhard; Leuchs, Gerd (IEEE Photonics Technology Letters, 2007)
The performance of a nonlinear amplifying loop mirror as a 2R-regenerator for return-to-zero differential-phase-shift-keyed signals has been investigated experimentally. The measured power characteristics and phase functions show that the signal amplitude is regenerated while the signal phase is preserved in the setup. A significant eye-opening improvement and a negative power penalty of about 1.5 dB were obtain
lhft_intern.bib::cvecek07

>30 dB Suppression of Intrinsic Backscattering in Whispering-Gallery-Mode Microresonators - Svela, Andreas O.; Silver, Jonathan M.; Del Bino, Leonardo; Zhang, Shuangyou; Woodley, Michael T.M.; Vanner, Michael R.; Del'Haye, Pascal (2021 Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings, 2021)
We demonstrate a technique for suppressing backscattered light in a whispering-gallery-mode resonator by positioning a sub-wavelength-size scatterer within its evanescent field, achieving at least 34 dB suppression compared to the intrinsic backscattering.
CRIS-Team Scopus Importer:2021-12-24

30 years of squeezed light generation - Andersen, Ulrik L.; Gehring, Tobias; Marquardt, Christoph; Leuchs, Gerd (Physica Scripta, 2016)
Squeezed light generation has come of age. Significant advances on squeezed light generation have been made over the last 30 years - from the initial, conceptual experiment in 1985 till today's top-tuned, application-oriented setups. Here we review the main experimental platforms for generating quadrature squeezed light that have been investigated in the last 30 years.
CRIS-Team Scopus Importer:2022-06-05
Keywords: entanglement; quantum optics; squeezed light

3.9-dB OSNR Gain by an NOLM-Based 2-R Regenerator - Meißner, Markus; Sponsel, Klaus; Cvecek, Kristian; Benz, S.; Weisser, B.; Schmauß, Bernhard; Leuchs, Gerd (IEEE Photonics Technology Letters, 2004)
We experimentally demonstrate bit-error-rate (BER) improvement of more than nine decades by an asymmetric nonlinear optical loop mirror (NOLM). This can be related to an optical signal-to-noise ratio (OSNR) gain of up to 3.9 dB with respect to the NOLM input OSNR at a bit rate of 40 GB/s. The principle of operation of NOLM-based 2-R regeneration with respect to BER improvement is investigated and it is experimentally shown that BER improvement cannot be detected directly at the regenerator's output. © 2004 IEEE.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.optik.1optik.39dbos

3D-imaging of human skin - optical in vivo tomography and topology by short coherence interferometry - Häusler, Gerd; et al. (Proceedings of SPIE, 1997)
We discuss different modifications of white light interferometry, for the acquisition of human skin morphology. In a first experiment we display the diffusion of light within tissue, versus time. Light is focused onto the surface of the sample, penetrates the sample, is scattered and partly emerges from the surface again. For each point of the surface we can measure a certain run time profile of the emerging photons, via the speckle contrast. The local scattering behavior of the skin is encoded in the run time profile. Further we present a sensor for the acquisition of cross-sectional images of volume scatterers, we call it "spectral radar." The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary, hence a short measurement time is possible. The depth uncertainty within a range of 1000 μm is about 10 μm. In first measurements we distinguished a melanoma maligna from healthy skin, in vitro and we measured the thickness of a fingernail in vivo. We further demonstrate a third method, the "coherence radar" for in vivo measurements of skin surface topology, with an accuracy of a few micrometers, and a field of 512 x 512 pixels. ©2004 Copyright SPIE - The International Society for Optical Engineering.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.optik.1optik.3dimag
Keywords: Coherence radar; Human skin; Multiple scattering; Oct; Short coherence interferometry; Skin cancer; Spectral radar; Texture analysis; Volume scatterer

3D Real Time Camera - Häusler, Gerd; et al. (Proc. of the 3rd Int. Workshop on Automatic Processing of Fringe Patterns, 1997)
UnivIS-Import:2015-04-16:Pub.1997.nat.dphy.optik.1optik.3dreal

3Dscript: animating 3D/4D microscopy data using a naturallanguage- based syntax. - Palmisano, Ralf; Tripal, Philipp; Schmid, Benjamin; Fraaß, Tina (https://www.quantitativebioimaging.com/qbi2020/conference-and-program-booklet/, 2020)
We introduce a software framework that assembles 3D animations of imaging data using a textual description with a syntax based on natural English language. In contrast to the established key frame based approach, smooth and complex motion sequences are intuitively implemented by concatenating multiple instructions. [1] The syntax is extensible and we demonstrate its integration into existing 3D visualization software. The user typically stores different rendering settings and scene transformations in a number of key frames along a timeline, and the rendering engine creates a smooth animation by interpolating between them. Key frames save the spatial transformation of an object as a state, e.g. three angles for a rotation, and not as a transition. This at least 4 key frames are required to define a 360- degree rotation with constant speed unambiguously. Even more are required if the motion is non-linear, which is essential for achieving smooth and pleasant motions. Software packages therefore typically provide a shortcut to insert key frames for rotations around common axes. More complex motions such as combined rotations around multiple axes, however, are difficult to achieve. The syntax based on natural English language maximizes experience and provides easy access for users of distinct fields. Each instruction is an English sentence. Complex motion sequences are implemented by combining multiple instructions which are applied in the order they appear in the text. The syntax comprises phrases for standard non-linear accelerations, resulting in smooth and natural animations. Self-defined macro functions can be used to define motion and other parameters as functions over time. We provide 3DScript as a Fiji/ImageJ plugin including an hardware-accelerated 3D renderer and a dedicated editor featuring auto-completion and recording. Although tailored to the included rendering engine, both the syntax and our animation framework can be easily adapted by other rendering software.<br
Keywords: 3D Animation; Natural Language Syntax; 3Dscript; Fiji/ImageJ Plug-In

8 QAM regeneration using a phase-sensitive amplifier with dual-conjugated pumps - Stiller, Birgit; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (Optics InfoBase Conference Papers, 2013)
CRIS-Team Scopus Importer:2021-06-29

Abandoned Functionality of Thin-Film Opal Photonic Crystals - Kuechenmeister, Jens; Wolff, Christian; Busch, Kurt; Peschel, Ulf; Romanov, Sergey (Advanced Optical Materials, 2013)
Angle-resolved polarized transmission spectra of thin-film opals are studied experimentally and theoretically as a function of the azimuthal rotation of the plane of incidence at different angles of light incidence. In such 3-dimensional lattices, the refraction acquires the form of diffraction orders, each with a distinct spectrum, that propagate simultaneously along different directions. The corresponding continuous and patchy stop-bands in the photonic energy band structure of the opal photonic crystal are determined numerically. For diffraction at high Miller index planes, the diffraction pattern is often distorted due to multiple-wave diffraction. The finite stacking of hexagonally close-packed layers leads to an intrinsic 3-fold rotation symmetry of these spectra, which is particularly pronounced in transmission for frequencies that correspond to wave vectors within the 1st Brillouin zone. Despite the cubic symmetry of the opal lattice, cross-polarization coupling effects occur in the volume of the opal crystal. These effects are associated with the fact that, the opal eigenmodes are Bloch waves whose electromagnetic field distributions and dispersion relations are markedly different from plane waves.
EAM Import::2019-03-13

About the scaling behavior of optical range sensors - Häusler, Gerd (Proc. of the 3rd Int. Workshop on Automatic Processing of Fringe Patterns, 1997)
UnivIS-Import:2015-04-16:Pub.1997.nat.dphy.optik.1optik.aboutt

Absolute calibration in grazing incidence interferometry via rotational averaging. - Mantel, Klaus Peter; Lamprecht, Jürgen; Lindlein, Norbert; Schwider, Johannes (Applied Optics, 2006)
Interferometry in grazing incidence can be used to test cylindrical mantle surfaces. The absolute accuracy of the resulting surface profiles is limited by systematic wavefront aberrations caused in the interferometer, in particular due to an inversion of the test wavefront in an interferometer using diffractive beam splitters. For cylindrical specimens, a calibration method using four positions has therefore been investigated. This test is combined with another method of optical metrology: the rotational averaging procedure. The implementation for grazing incidence is described and measurement results for hollow cylinders are presented. The gain in accuracy is demonstrated.
UnivIS-Import:2015-04-14:Pub.2006.nat.dphy.optik.1optik.absolu

Absolute frequency measurement of iodine lines with a femtosecond optical synthesizer - Holzwarth, R; Nevsky, Alexander; Zimmermann, Marcus; Udem, Thomas; Hänsch, Theodor; von Zanthier, Joachim; Walther, Herbert; Knight, J C; Wadsworth, William; Russell, Philip St. John; Skvortsov, M N; Bagayev, S N (Applied Physics B-Lasers and Optics, 2001)
We have used a single laser femtosecond (.)optical frequency synthesizer together with a widely tunable Nd:YAG laser to measure the absolute frequency of several absorption lines in molecular iodine around 532 nm. The use of two different repetition frequencies allows us to determine the number of modes used for the frequency measurement unambiguously. The lines also provide data for the determination of improved ro-vibrational constants of the iodine molecule.

Absolute sphericity measurement: a comparative study of the use of interferometry and a Shack-Hartmann sensor - Lindlein, Norbert; et al. (Optics Letters, 1998)
A comparison of absolute sphericity measurements with a Shack-Hartmann sensor and a Twyman-Green interferometer is presented. The absolute deviations of a test sphere from its ideal shape were calculated in both cases from the measured wave aberrations of three different positions. Very good qualitative and quantitative agreement of the results was achieved. The difference of the root-mean-square values of the two methods was 1/1000 of a wavelength. © 1998 Optical Society of America.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.absolu

Absolute sphericity measurement: a comparative study on the use of interferometry and a Shack-Hartmann sensor - Lindlein, Norbert; et al. (Proceedings of the 1998 International Symposium on Information Theory, CLEO/EUROPE'98, 1998)
A comparative study of the performance of the Shack-Hartmann sensor (SHS) and interferometry in absolute sphericity tests was conducted. The absolute sphericity test was carried out with an existing TWG using the phase shifting technology. The same set-up and identical measurements were used to measure the wave fields in front of the SHS. For the SHS measurements, the reference arm of the TWG was obscured. The measured concave surface had a diameter of 40mm and a radius of curvature of 41mm. The used wavelength was λ=632.8nm and the distance of the contours in the plots is 0.050λ.

Absolute testing of aspherics in transmitted light using an amplitude DOE - Lindlein, Norbert; et al. (6th International Workshop on Advanced Optical Metrology, Fringe 2009, 2009)

Absolute testing of the reference surface of a Fizeau interferometer through even/odd decompositions - Schreiner, Roland; Schwider, Johannes; Lindlein, Norbert; Mantel, Klaus Peter (Applied Optics, 2008)
Absolute testing of spherical surfaces is a technological necessity because of increased accuracy requirements. In a Fizeau setup, the main part of the interferometer deviations thereby comes from the reference surface. We demonstrate the validity of an absolute testing procedure for the reference surface that has been proposed earlier. The procedure relies on the decomposition of the surface deviations into odd and even parts and could be used in partially coherent illumination. The odd deviations are obtained from a basic and a 180°-rotated position of an auxiliary sphere, and the even deviations can be measured with the help of a cat's eye position in double pass using an opaque half screen in the interferometer aperture. © 2008 Optical Society of America.
UnivIS-Import:2015-04-14:Pub.2008.nat.dphy.optik.1optik.absolu

Absoluttest von rotationssymmetrischen Asphären mittels radialem Shearing - Mantel, Klaus; Geist, Eduard; Harder, Irina; Lindlein, Norbert (DGAO-Proceedings, 2010)

Absolutverfahren zum Nulltest asphärischer Linsen im Durchlicht - Berger, Andreas; Mantel, Klaus; Harder, Irina; Lindlein, Norbert (114. Jahrestagung der DGaO, 2013)

Accessing the Phase Quadrature of Intense Non-Classical Light States - Leuchs, Gerd; et al. (Quantum Information with continuous variables of atoms and light, 2007)
UnivIS-Import:2015-04-20:Pub.2007.nat.dphy.optik.1optik.access

Achieving Gaussian outputs from large-mode-area higher-order-mode fibers - Lindlein, Norbert; Leuchs, Gerd; Ramachandran, Srinivasan (Applied Optics, 2007)
We describe an alternative to fiber-gratings for converting higher-order LP0om (m > 1) fiber modes into a nearly fundamental Gaussian shape at the output of a fiber. This schematic enables the use of light propagation in higher-order modes of a fiber, a fiber-platform that has recently shown great promise for achieving very large mode areas needed for future high-power lasers and amplifiers. The conversion will be done by using a binary phase plate in the near field of the fiber, which emits the LPom mode. Since the binary phase plate alone cannot increase the quality factor M2 of the laser beam because of some broad sidebands, a filtering of the sidebands is done in the Fourier plane of a telescope. Of course, this will cost some of the total light power, but on the other side the M2 factor can be reduced to nearly the ideal value near 1.0, and it is shown that ∼76% of the total light power can be conserved for all investigated modes (2≤m≤8). A tolerance analysis for the phase plate and its adjustment is made, and different optical imaging systems to form a magnified image of the fiber mode on the phase plate are discussed in order to have more tolerance for the adjustment of the phase plate. © 2007 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.optik.1optik.achiev

Achromatic diffractive fan-out systems - Lindlein, Norbert; et al. (Proceedings of SPIE, 1994)
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.optik.1optik.achrom

A complete basis of generalized Bell states - Sych, Denis; Leuchs, Gerd (New Journal of Physics, 2009)
A generalization of the Bell states and Pauli matrices to dimensions which are powers of 2 is considered. A basis of maximally entangled multidimensional bipartite states (MEMBS) is chosen very similar to the standard Bell states and constructed of only symmetric and antisymmetric states. This special basis of MEMBS preserves all basic properties of the standard Bell states. We present a recursive and non-recursive method for the construction of MEMBS and discuss their properties. The antisymmetric MEMBS possess the property of rotationally invariant exclusive correlations which is a generalization of the rotational invariance of the antisymmetric singlet Bell state. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
UnivIS-Import:2015-04-14:Pub.2009.nat.dphy.optik.1optik.acompl

A confocal profilometer using microlens arrays - Lindlein, Norbert; et al. (Technical digest / Optical Society of America, 1998)
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.aconfo

Active laser frequency stabilization using neutral praseodymium (Pr) - Oppel, Steffen; Guthörlein, G. H.; Kaenders, W.; von Zanthier, Joachim (Applied Physics B-Lasers and Optics, 2010)
We present a new possibility for the active frequency stabilization of a laser using transitions in neutral praseodymium. Because of its five outer electrons, this element shows a high density of energy levels leading to an extremely line-rich excitation spectrum with more than 25 000 known spectral lines ranging from the UV to the infrared. We demonstrate the active frequency stabilization of a diode laser on several praseodymium lines between 1105 and 1123 nm. The excitation signals were recorded in a hollow cathode lamp and observed via laser-induced fluorescence. These signals are strong enough to lock the diode laser onto most of the lines by using standard laser locking techniques. In this way, the frequency drifts of the unlocked laser of more than 30 MHz/h were eliminated and the laser frequency stabilized to within 1.4(1) MHz for averaging times > 0.2 s. Frequency quadrupling the stabilized diode laser can produce frequency-stable UV-light in the range from 276 to 281 nm. In particular, using a strong hyperfine component of the praseodymium excitation line E=16 502.616(7/2) cm(-1) -> E = 25442.742(9/2)(0) cm(-1) at lambda=1118.5397(4) nm makes it possible-after frequency quadruplication-to produce laser radiation at lambda/4=279.6349(1) nm, which can be used to excite the D(2) line in Mg(+).

Adaptive frequency comb illumination for interferometry in the case of nested two-beam cavities - Harder, Irina; Leuchs, Gerd; Mantel, Klaus Peter; Schwider, Johannes (Applied Optics, 2011)

Addressing RB and CS transitions with a tunable source of photon pairs - Schunk, Gerhard; Vogl, Ulrich; Förtsch, Michael; Strekalov, Dmitry; Sedlmeir, Florian; Schwefel, Harald G.L.; Leuchs, Gerd; Marquardt, Christoph (Optics InfoBase Conference Papers, 2014)
CRIS-Team Scopus Importer:2022-06-05

Adjustable diffractive spiral phase plates - Harn, Walter; Bernet, Stefan; Ritsch-Marte, Monica; Harder, Irina; Lindlein, Norbert (Optics Express, 2015)

Adsorption and self-assembly of porphyrins on ultrathin CoO films on Ir(100) - Xiang, Feifei; Schmitt, Tobias; Raschmann, Marco; Schneider, M. Alexander (Beilstein Journal of Nanotechnology, 2020)
Porphyrins represent a versatile class of molecules, the adsorption behavior of which on solid surfaces is of fundamental interest due to a variety of potential applications. We investigate here the molecule-molecule and molecule-substrate interaction of Co-5,15-diphenylporphyrin (Co-DPP) and 2H-tetrakis(p-cyanophenyl)porphyrin (2H-TCNP) on one bilayer (1BL) and two bilayer (2BL) thick cobalt oxide films on Ir(100) by scanning tunneling microscopy (STM) and density functional theory (DFT). The two substrates differ greatly with respect to their structural and potential-energy landscape corrugation with immediate consequences for adsorption and self-assembly of the molecules studied. On both films, an effective electronic decoupling from the metal substrate is achieved. However, on the 1BL film, Co-DPP molecules are sufficiently mobile at 300 K and coalesce to self-assembled molecular islands when cooled to 80 K despite their rather weak intermolecular interaction. In contrast, on the 2BL film, due to the rather flat potential landscape, molecular rotation is thermally activated, which effectively prevents self-assembly. The situation is different for 2H-TCNPP, which, due to the additional functional anchoring groups, does not self-assemble on the 1BL film but forms self-assembled compact islands on the 2BL film. The findings demonstrate the guiding effect of the cobalt oxide films of different thickness and the effect of functional surface anchoring.
CRIS-Team WoS Importer:2020-10-23

Adsorption Behavior of a Cyano-Functionalized Porphyrin on Cu(111) and Ag(111): From Molecular Wires to Ordered Supramolecular Two-Dimensional Aggregates - Lepper, Michael; Schmitt, Tobias; Gurrath, Martin; Raschmann, Marco; Zhang, Liang; Stark, Michael Werner; Hölzel, Helen; Jux, Norbert; Meyer, Bernd; Schneider, M. Alexander; Steinrück, Hans-Peter; Marbach, Hubertus (Journal of Physical Chemistry C, 2017)
We investigate the impact of peripheral cyano functionalization of the previously well-studied 2H-tetraphenylporphyrin (2HTPP) by scanning tunneling microscopy (STM) and density functional theory (DFT). The adsorption behavior of 2H-tetralds(p-cyano)-phenylporphyrin (2HTCNPP) is studied at room temperature and at 80 K on Cu(111) and Ag(111). Interestingly, the cyano-functionalized porphyrins tend to form isolated ID chains on Cu(111), in particular after mild annealing at 350 K. The individual 2HTCNPPs as well as the formed chains are oriented along the main crystallographic directions of the Cu(111) substrate due to a strongly attractive and site-specific interaction between the iminic nitrogens of the 2HTCNPP and Cu substrate atoms. The linking within the 1D molecular chains is realized by Cu adatoms as evidenced by comparison of STM and DFT. In contrast, on Ag(111) the molecules assemble into 2D supramolecular layers with long-range order and a square unit cell, stabilized by molecule-molecule interactions. The orientation of the molecules with respect to the unit cell lattice vectors leads to organizational chirality. By codeposition of cobalt, the porphyrin molecules are metalated at room temperature. We did not observe any evidence for metal-organic network formation on Ag(111), even after varying the deposition parameters or the order of metal and porphyrin deposition. Our study shows that cyano functionalization of porphyrins can give rise to novel and unique self-assembled structures like 1D molecular chains without any cross-connections via adatom linking.

A Fibre-Optical Implementation of Range Sensors, based on the 'Spectral Radar' - Häusler, Gerd; et al. (Proceedings of the EOS Topical Meeting Free Space Micro-Optical Systems, 1996)
UnivIS-Import:2015-04-16:Pub.1996.nat.dphy.optik.1optik.afibre

After-gate attack on a quantum cryptosystem - Wiechers, C.; Lydersen, L.; Wittmann, C.; Elser, Dominique Alexander; Skaar, Johannes; Marquardt, Christoph; Makarov, V.; Leuchs, Gerd (New Journal of Physics, 2011)
We present a method to control the detection events in quantum key distribution systems that use gated single-photon detectors. We employ bright pulses as faked states, timed to arrive at the avalanche photodiodes outside the activation time. The attack can remain unnoticed, since the faked states do not increase the error rate per se. This allows for an intercept-resend attack, where an eavesdropper transfers her detection events to the legitimate receiver without causing any errors. As a side effect, afterpulses, originating from accumulated charge carriers in the detectors, increase the error rate. We have experimentally tested detectors of the system id3110 (Clavis2) from ID Quantique. We identify the parameter regime in which the attack is feasible despite the side effect. Furthermore, we outline how simple modifications in the implementation can make the device immune to this attack. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
CRIS-Team Scopus Importer:2022-06-05

A generator for unique quantum random numbers based on vacuum states - Gabriel, Christian; Wittmann, Christoffer; Sych, Denis; Dong, Ruifang; Mauerer, Wolfgang; Andersen, Ulrik L.; Marquardt, Christoph; Leuchs, Gerd (Nature Photonics, 2010)
Random numbers are a valuable component in diverse applications that range from simulations1 over gambling to cryptography2,3. The quest for true randomness in these applications has engendered a large variety of different proposals for producing random numbers based on the foundational unpredictability of quantum mechanics4-11. However, most approaches do not consider that a potential adversary could have knowledge about the generated numbers, so the numbers are not verifiably random and unique 12-15. Here we present a simple experimental setup based on homodyne measurements that uses the purity of a continuous-variable quantum vacuum state to generate unique random numbers. We use the intrinsic randomness in measuring the quadratures of a mode in the lowest energy vacuum state, which cannot be correlated to any other state. The simplicity of our source, combined with its verifiably unique randomness, are important attributes for achieving high-reliability, high-speed and lowcost quantum random number generators. © 2010 Macmillan Publishers Limited. All rights reserved.
CRIS-Team Scopus Importer:2022-06-05

Agile and Versatile Quantum Communication: Signatures and Secrets - Richter, Stefan; Thornton, Matthew; Khan, Imran; Scott, Hannah; Jaksch, Kevin; Vogl, Ulrich; Stiller, Birgit; Leuchs, Gerd; Marquardt, Christoph; Korolkova, Natalia (Physical Review X, 2021)
Agile cryptography allows for a resource-efficient swap of a cryptographic core in case the security of an underlying classical cryptographic algorithm becomes compromised. Conversely, versatile cryptography allows the user to switch the cryptographic task without requiring any knowledge of its inner workings. In this paper, we suggest how these related principles can be applied to the field of quantum cryptography by explicitly demonstrating two quantum cryptographic protocols, quantum digital signatures (QDS) and quantum secret sharing (QSS), on the same hardware sender and receiver platform. Crucially, the protocols differ only in their classical postprocessing. The system is also suitable for quantum key distribution (QKD) and is highly compatible with deployed telecommunication infrastructures, since it uses standard quadrature phase-shift keying encoding and heterodyne detection. For the first time, QDS protocols are modified to allow for postselection at the receiver, enhancing protocol performance. The cryptographic primitives QDS and QSS are inherently multipartite, and we prove that they are secure not only when a player internal to the task is dishonest, but also when (external) eavesdropping on the quantum channel is allowed. In our first proof-of-principle demonstration of an agile and versatile quantum communication system, the quantum states are distributed at GHz rates. A 1-bit message may be securely signed using our QDS protocols in less than 0.05 ms over a 2-km fiber link and in less than 0.2 s over a 20-km fiber link. To our knowledge, this also marks the first demonstration of a continuous-variable direct QSS protocol.
CRIS-Team Scopus Importer:2021-03-19

A highly miniaturized satellite payload based on a spatial heterodyne spectrometer for atmospheric temperature measurements in the mesosphere and lower thermosphere - Kaufmann, Martin; Olschewski, Friedhelm; Mantel, Klaus; Solheim, Brian; Shepherd, Gordon; Deiml, Michael; Liu, Jilin; Song, Rui; Chen, Qiuyu; Wroblowski, Oliver; Wei, Daikang; Zhu, Yajun; et al. (Atmospheric Measurement Techniques, 2018)
A highly miniaturized limb sounder for the observation of the O2 A-Band to derive temperatures in the mesosphere and lower thermosphere is presented. The instrument consists of a monolithic spatial heterodyne spectrometer (SHS), which is able to resolve the rotational structure of the R-branch of that band. The relative intensities of the emission lines follow a Boltzmann distribution and the ratio of the lines can be used to derive the kinetic temperature. The SHS operates at a Littrow wavelength of 761.8 nm and heterodynes a wavelength regime between 761.9 nm and 765.3 nm with a resolving power of about 8000 considering apodization effects. The size of the SHS is 38 × 38 × 27 mm3 and its acceptance angle is ±5°. It has an etendue of 0.014 cm2 sr. Complemented by a front optics with a solid angle of 0.65° and a detector optics, the entire optical system fits into a volume of about 1.5 liters. This allows to fly this instrument on a 3 or 6 unit CubeSat. The vertical field of view of the instrument is about 60 km at the Earth's limb if operated in a typical low Earth orbit. Integration times to obtain an entire altitude profile of nighttime temperatures are in the order of one minute for a vertical resolution of 1.5 km and a random noise level of 1.5 K. Daytime integration times are one order of magnitude shorter. This work presents the design parameters of the optics and a radiometric assessment of the instrument. Furthermore it gives an overview of the required characterization and calibration steps. This includes the characterization of image distortions in the different parts of the optics, flat fielding and the spectral power estimatio

A High-Rate Receiver for Satellite Quantum Key Distribution - Rößler, Conrad; Günthner, Kevin; Hacker, Bastian; Leuchs, Gerd; Marquardt, Christoph; Leuchs, Gerd (Optics InfoBase Conference Papers, 2022)
We present a high-rate fiber-integrated quantum receiver for phase-encoded satellite-based QKD. We highlight concepts for time synchronization as well as compensation of the Doppler shift and optimized quantum signal processing.
CRIS-Team Scopus Importer:2022-09-02

A high-speed secure quantum random number generator based on vacuum states - Gabriel, Christian; Wittmann, Christoffer; Hacker, Bastian; Mauerer, Wolfgang; Huntington, Elanor; Sabuncu, Metin; Marquardt, Christoph; Leuchs, Gerd (2012 Conference on Lasers and Electro-Optics, CLEO 2012, 2012)
A high-speed continuous-variable quantum random bit generator with an expected effective bit generation rate of up to 10 GBit/s is presented. The obtained bit sequences are truly random and unique, i.e. they cannot be known by an adversary. © 2012 OSA.
CRIS-Team Scopus Importer:2022-06-05

A high throughput device for label-free real-time study of cellular secretion with iSCAT microscopy - Gemeinhardt, Andre; König, Katharina; Dahmardeh, Mahyar; Sandoghdar, Vahid (Optics InfoBase Conference Papers, 2020)
We use interferometric scattering microscopy (iSCAT) to study in-situ secretion dynamics of living cells. The method allows us to optically detect single proteins in real-time without the need for labeling.
CRIS-Team Scopus Importer:2020-10-02

A Holography-Based Modal Wavefront Sensor for the Precise Positioning of a Light Emitter Using a High-Resolution Computer-Generated Hologram - Loosen, Florian; Stehr, Johannes; Alber, Lucas; Harder, Irina; Lindlein, Norbert (Ieee Photonics Journal, 2018)
In certain applications, modal wavefront sensors (MWFSs) can outperform zonal wavefront sensors, which are widely used due to their high ﬂexibility. In this paper, a holography-based MWFS as described is developed for the fast position control of a light emitter in a deep parabolic mirror. The light source is located in the vicinity of the focal point. Instead of Zernike polynomials, more complex phase functions, which are related to certain dislocations of the light source are used as detector modes. The performance of the sensor is veriﬁed with a test setup, where the test wavefront is generated by a spatial light modulator instead of a real parabolic mirror. The design and fabrication of the required high-resolution holographic element is described and an easy way of multiplexing several single mode sensors is demonstrated.
Keywords: advanced optics design; diffractive optics; holography

Akquisition und Verarbeitung von 3D-Daten für die angewandte Messtechnik - Häusler, Gerd; et al. (Bildverarbeitung '97: Forschen, Entwickeln, Anwenden, 1997)
UnivIS-Import:2015-04-16:Pub.1997.nat.dphy.optik.1optik.akquis

Algorithm for expanding the dynamic range of a Shack-Hartmann sensor by using a spatial light modulator array - Lindlein, Norbert; et al. (Optical Engineering, 2001)
Normally, the dynamic range of a Shack-Hartmann sensor is limited by the foci leaving their respective subapertures, thus a definite attachment of the foci to their subapertures is difficult. By using an array of spatial light modulators in front of the microlenses of the sensor to switch on and off the subapertures, a definite assignment of the spots to their subapertures is possible. We present a coding algorithm that needs only log2 N+1 frames to assign N spots unequivocal to their subapertures. © 2001 Society of Photo-Optical Instrumentation Engineers.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.optik.1optik.algori
Keywords: Coding algorithm; Microlenses; Shack-Hartmann sensor; Spatial light modulator

All-fibre source of amplitude squeezed lightpulses - Meißner, Markus; Marquardt, Christoph; Heersink, Joel; Gaber, Tobias; Wietfeld, André; Leuchs, Gerd; Andersen, Ulrik Lund (Journal of Optics B Quantum and Semiclassical Optics, 2004)
An all-fibre source of amplitude squeezed solitons utilizing the self-phase modulation in an asymmetric Sagnac interferometer is experimentally demonstrated. The asymmetry of the interferometer is passively controlled by an integrated fibre coupler, allowing for the optimization of the noise reduction. We have carefully studied the dependence of the amplitude noise on the asymmetry and the power launched into the Sagnac interferometer. Qualitatively, we find good agreement between the experimental results, a semi-classical theory and earlier numerical calculations (Schmitt et al 1998 Phys. Rev. Lett. 81 2446). The stability and flexibility of this all-fibre source makes it particularly well suited to applications in quantum information science.<br
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.optik.1optik.allfib

All-fibre source of continuous variable entangled light - Leuchs, Gerd; et al. (International Journal of Modern Physics B, 2006)
We experimentally demonstrate the production of continuous variable entanglement of femto second laser pulses from an all-fibre asymmetric Sagnac interferometer exploiting the Kerr effect. Contrary to the experiment of Silberhorn et al. [Phys. Rev. Lett. 86,4267 (2001)], the asymmetric coupler in the Sagnac loop is fully integrated in the fibre, making the source extremely compact, reliable and robust. Employing a simple detection scheme, comprising a beam splitter and two intensity detectors, we clearly observe quantum correlations of conjugate quadratures, hereby witnessing entanglement. © World Scientific Publishing Company.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.allfib
Keywords: Continuous variables; Entanglement; Sagnac interferometer

All normal dispersion nonlinear fiber source for Hyperspectral Stimulated Raman Scattering Microscopy - Abdolghader, Pedram; Pegoraro, Adrian F.; Joly, Nicolas; Ridsdale, Andrew; Lausten, Rune; Stolow, Albert (2019 Photonics North, PN 2019, 2019)
— we demonstrate the use a low noise all-normal-dispersion nonlinear fiber as a supercontinuum light source for Hyperspectral Stimulated Raman Scattering microscopy.
CRIS-Team Scopus Importer:2019-10-08
Keywords: Low noise super continuum generation; Nonlinear microscopy; Stimulated Raman Microscopy

All normal dispersion nonlinear fibre supercontinuum source characterization and application in hyperspectral stimulated Raman scattering microscopy - Abdolghader, Pedram; Pegoraro, Adrian F.; Joly, Nicolas; Ridsdale, Andrew; Lausten, Rune; Légaré, François; Stolow, Albert (Optics Express, 2020)
Hyperspectral stimulated Raman scattering (SRS) microscopy is a powerful label-free, chemical-specific technique for biomedical and mineralogical imaging. Usually, broad and rapid spectral scanning across Raman bands is required for species identification. In many implementations, however, the Raman spectral scan speed is limited by the need to tune source laser wavelengths. Alternatively, a broadband supercontinuum source can be considered. In SRS microscopy, however, source noise is critically important, precluding many spectral broadening schemes. Here we show that a supercontinuum light source based on all normal dispersion (ANDi) fibres provides a stable broadband output with very low incremental source noise. We characterized the noise power spectral density of the ANDi fibre output and demonstrated its use in hyperspectral SRS microscopy applications. This confirms the viability and ease of implementation of ANDi fibre sources for broadband SRS imaging.
CRIS-Team Scopus Importer:2020-12-11

All-optical DPSK-Signal-Regeneration based on a NOLM-Setup - Striegler, Arne; Meißner, Markus; Cvecek, Kristian; Sponsel, Klaus; Schmauß, Bernhard (Optical Fiber Technology, 2005)
We present a novel concept for all-optical DPSK signal regeneration based on a directionally attenuated non linear loop mirror (DA-NOLM). © 2005 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2005.tech.IE.LEH.allopt

All-Optical Multilevel Amplitude and Phase Regeneration - Röthlingshöfer, Tobias; Richter, T.; Onishchukov, Georgy; Schubert, C.; Schmauß, Bernhard; Leuchs, Gerd (2014 IEEE Photonics Society Summer Topical Meeting Series, 2014)
Using a cascade of an amplitude and a phase regenerator, multilevel signal processing is demonstrated experimentally for a 25-GBd star-8QAM. Improvements in the signal quality by up to 2 dB are obtaine
lhft_intern.bib::Roethlingshoefer2014_6

All-optical phase-preserving multilevel amplitude regeneration - Röthlingshöfer, Tobias; Richter, Thomas; Schubert, Colja; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (Optics Express, 2014)
The possibility of all-optical phase-preserving amplitude regeneration for star-8QAM is demonstrated using a modified nonlinear optical loop mirror. Experiments show a reduction in amplitude noise on both amplitude levels simultaneously, considering two different types of signal distortions: deterministic low-frequency amplitude modulation and broadband amplitude noise. Furthermore, using this amplitude regeneration, the robustness against nonlinear phase noise from fiber nonlinearity in a transmission line is increased. The scheme suppresses the conversion of amplitude noise to nonlinear phase noise. This is shown for simultaneous amplitude regeneration of the two amplitude states as well as for amplitude regeneration of the high-power states only. If the transmission is limited by nonlinear phase noise, single-level operation at the more critical higher-power state will benefit because of the wider plateau region. Numerical simulations confirm the experimental result

All-optical signal regeneration of advanced modulation formats - Röthlingshöfer, Tobias; Richter, Thomas; Stiller, Birgit; Onishchukov, Georgy; Schubert, Colja; Schmauß, Bernhard; Leuchs, Gerd (Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XIII, 2014)
With growing demand on transmission capacity, spectral-efficient multilevel modulation formats such as quadrature amplitude modulation (QAM) become of great interest. One of their weaknesses is high sensitivity to noise accumulation, especially in long-haul transmission systems. Our investigations have shown the possibility of all-optical regeneration of multiple amplitude and phase states. Processing of amplitude noise in several amplitude states is based on periodicity of interference conditions in modified nonlinear fiber Sagnac interferometers. Their staircase-like power transfer characteristic can be used for phase-preserving amplitude regeneration of multiple amplitude states. Processing of QAM with up to three non-zero amplitude states, e.g. 16QAM, has been demonstrated in numerical simulations. Furthermore, simultaneous amplitude regeneration of a star-8QAM format with two amplitude states was performed experimentally. Recently, it has also been shown that phase-sensitive amplification for multiple phase states can be realized in fiber optical parametric amplifiers using four-wave mixing (FWM) with a high-order idler. Our numerical simulations and experimental results for star-8QAM revealed that with some modifications, this approach can be used not only for reduction of phase noise in multilevel phase-shift keying but also for signals with multiple amplitude states. The transmission improvement using a cascade of these two regenerator types has been demonstrated in numerical simulations and experiments. Numerical investigations confirm also the possibility to combine both approaches in a single device by using the highly nonlinear fiber in the Sagnac interferometer loop simultaneously for phase-sensitive amplification in one propagation direction. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use onl
lhft_intern.bib::Roethlingshoefer2014_8

All-Optical Simultaneous Multilevel Amplitude and Phase Regeneration - Röthlingshöfer, Tobias; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (IEEE Photonics Technology Letters, 2014)
Simultaneous amplitude and phase noise reduction of multiple signal states using a nonlinear amplifying loop mirror with integrated directional phase-sensitive amplifier are presented for the star-eight quadrature amplitude modulation transmission format as an example. The performance of this combined regenerator scheme is compared with that of a cascade of separate phase and amplitude regenerators. It could be shown that an improvement in the error vector magnitude of 4 dB for the high-power states with simultaneous improvement of 5 dB for the low-power states is possible in both cases. Transmission improvement by regeneration is considered for two noise types: 1) amplified spontaneous emission and 2) nonlinear phase noise. Both schemes can either improve the bit error rate by an order of magnitude or enable an increase of the fiber launch power by 3 d
lhft_intern.bib::Roethlingshoefer2014a

All-sky Measurement of the Anisotropy of Cosmic Rays at 10 TeV and Mapping of the Local Interstellar Magnetic Field - Abeysekara, A. U.; Alfaro, R.; Alvarez, C.; Arceo, R.; Arteaga-Velazquez, J. C.; Avila Rojas, D.; Belmont-Moreno, E.; Benzvi, S. Y.; Brisbois, C.; Capistran, T.; Carramiana, A.; Casanova, S.; et al. (Astrophysical Journal, 2019)
We present the first full-sky analysis of the cosmic ray arrival direction distribution with data collected by the High-Altitude Water Cherenkov and IceCube observatories in the northern and southern hemispheres at the same median primary particle energy of 10 TeV. The combined sky map and angular power spectrum largely eliminate biases that result from partial sky coverage and present a key to probe into the propagation properties of TeV cosmic rays through our local interstellar medium and the interaction between the interstellar and heliospheric magnetic fields. From the map, we determine the horizontal dipole components of the anisotropy δ 0h = 9.16 ×10 -4 and δ 6h = 7.25 ×10 -4 (±0.04 × 10 -4 ). In addition, we infer the direction (229.°2 ± 3.°5 R.A., 11.°4 ± 3.°0 decl.) of the interstellar magnetic field from the boundary between large-scale excess and deficit regions from which we estimate the missing corresponding vertical dipole component of the large-scale anisotropy to be δN ∼ -3.97 +1.0 -2.0 × 10 -4 .
CRIS-Team Scopus Importer:2019-05-02
Keywords: astroparticle physics; cosmic rays; ISM: magnetic fields

A miniaturized satellite payload hosting a spatial heterodyne spectrometer for remote sensing of atmospheric temperature - Kaufmann, Martin; Deiml, Michael; Olschewski, Friedhelm; Mantel, Klaus; Wagner, Fritz; Loosen, Florian; Fröhlich, Denis; Rongen, Heinz; Neubert, Tom; Rottland, Björn; Schneider, Herbert; Riese, Martin; et al. (Proceeding, 11. IAA Symposium on Small Satellites for Earth Observation, 2017)
In this paper we present a concept study for a highly miniaturized interferometer for the deployment  on  micro-  and  nano-satellites  to  measure  atmospheric  temperature.  The  selected technology  is  a  Spatial  Heterodyne  Spectrometer  (SHS).  It  is  known  since  1958,  but  its manufacturability  gained  increasing  attention  during  the  last  decade  because  of  improvements  in detector and computer technology. The throughput of a SHS is orders of magnitude larger than of a conventional  grating  spectrometer  of  the  same  size.  It  can  be  designed  to  deliver  extraordinary spectral  resolution  to  resolve  individual  emission  or  absorption  lines,  or  even  Doppler  shifts.  We introduce the SHS technology and an instrument design to measure the ro-vibrational structure of the O2  atmospheric band at 762 nm in limb viewing geometry. Design considerations of a potential SHS spectrometer and of the overall optical system are discussed. Requirements for a potential satellite platform hosting this instrument are presented, in particular in view of the utilization of CubeSats or other  nano-satellite  platforms.  Potential  mission  scenarios  for  three-dimensional  sounding  of   the atmosphere taking advantage of the agility of small satellites are given.

Amplification of Microwave Signals at the Quantum Limit - Eichler, Christopher (Meeting of the CCQED fellows, 2014)
Keywords: wwwqudev

Amplitude noise reduction in multilevel QAM formats using a nonlinear amplifying loop mirror with a saturable amplifier - Roethlingshoefer, Tobias; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference, 2011)
lhft_intern.bib::Roethlingshoefer2011

Analysis and optimization of coupling to external cavities in feedback experiments with vertical-cavity surface-emitting lasers - Jentsch, Karl Friedrich; Sondermann, Markus; Ackemann, Thorsten (Optics Communications, 2008)
The feedback strength is a crucial parameter for feedback experiments using semiconductor lasers. In this article, the coupling efficiency of the field of vertical-cavity surface-emitting lasers (VCSELs) to external cavities containing one collimating lens has been analyzed in detail using ABCD-matrix methods. It is found that for a given set of parameters there are two distinct, experimentally realizable positions of the collimating lens which allow for optimal coupling, if the cavity length is sufficiently small. The predictions are verified in experiments using single-transverse-mode VCSELs. The obtained coupling efficiencies exceed 70%. © 2007 Elsevier B.V. All rights reserved.
Keywords: Coupling efficiency; Feedback; Vertical-cavity surface-emitting lasers

Analysis of additive manufactured polymer optical waveguides: measurement and simulation of their waviness - Backhaus, Carsten; Hoffmann, Gerd-Albert; Reitberger, Thomas; Eiche, Yannic; Overmeyer, Ludger; Franke, Jörg; Lindlein, Norbert (Integrated Optics: Devices, Materials, and Technologies XXIV, 2020)
This paper analyzes an approach for additively manufacturing polymer optical waveguides. The production process includes flexographic printing of conditioning lines (5 μm height) on a substrate, which are used as guiding barriers in the subsequent printing of the optical core. The core is additively printed (up to 50 μm in height) with an aerosol jet printer, filling the gap between the conditioning lines. The conditioning lines do not only enhance the contact angle of the polymer, which results in a higher cross section of the waveguides, but also improve the straight edges of the printed waveguides. We show that the quality of the conditioning lines is directly correlated to the waviness of the waveguides. Consequently, the analyses of the waviness of the conditioning lines classifies the quality of the fabricated waveguides. However, the waviness of the waveguides can also be considered in optical simulations. In this paper we show how we derive a waveguide model with waviness by fitting a single sine function onto the topological data of the conditioning lines. With this model a variation of the waviness can easily be simulated and goals for fabrication can be set. With the simulations it is possible to verify that the measured waviness (period of 559.5 μm and an amplitude of 4.99 μm) does not affect the optical quality of the waveguide
Keywords: Polymer Optical Waveguides; Waviness; Additive Manufacturing; Waveguide Simulation; Aerosol Jet Printing

Analysis of the disturbing diffraction orders of computer-generated holograms used for testing optical aspherics - Lindlein, Norbert (Applied Optics, 2001)
Aspheric surfaces are increasingly used in the design of high-quality optical imaging systems. Therefore accurate testing methods for aspherics are also necessary. One possibility is to use a computer-generated hologram (CGH) as a part of a null lens in an interferometric testing device. However, CGHs normally have more than one diffraction order, thus causing disturbing areas in the interferogram. Here a simple approximative analytical expression is given for the spatial frequencies of the disturbing light in the interferogram coming from the different diffraction orders of the CGH. This expression also enables one to calculate the size and the shape of the disturbing areas in the interferogram. Some design examples for CGHs are given in an application of the expression. © 2001 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.optik.1optik.analys

Analysis of the signal measured in spectral-domain optical coherence tomography based on nonlinear interferometers - Rojas-Santana, Arturo; Machado, Gerard J.; Chekhova, Maria; Lopez-Mago, Dorilian; Torres, Juan P. (Physical Review A, 2022)
We analyze and compare the output signals obtained in three different configurations of optical coherence tomography (OCT). After appropriate processing, these signals are used to retrieve an image of the sample under investigation. One of the configurations considered is the common choice in most OCT applications and is based on the use of a Michelson interferometer. For brevity, here we refer to it as standard OCT. The other two configurations are two types of optical coherence tomography based on the use of so-called nonlinear interferometers, interferometers that contain optical parametric amplifiers inside. The goal is to highlight the differences and similarities between the output signals measured in standard OCT and in these two OCT schemes, with the aim of evaluating if retrieval of information about the sample can be better done in one case over the others. We consider schemes where the optical sectioning of the sample is obtained by measuring the output signal spectrum (spectral or Fourier-domain OCT), since it shows better performance in terms of speed and sensitivity than the counterpart time-domain OCT.
CRIS-Team Scopus Importer:2022-09-30

Analytical circuit model for split ring resonators in the far infrared and optical frequency range - Delgado, V.; Sydoruk, Oleksiy; Tatartschuk, Eugen; Marqués, R.; Freire, M. J.; Jelinek, L. (Metamaterials, 2009)
The article proposes an LC-circuit model for single split ring resonators (SRRs) operating at far infrared and optical frequencies. Taking the effects of magnetic and kinetic inductances as well as gap and surface capacitances into account, we obtain analytical expressions for the resonant frequency of the singly, doubly, and quadruply split SRRs. Comparing the analytical results with numerical simulations, we show that the numerical simulations agree better with the present model than with the models reported previously. We also discuss a size dependent correction to the electron collision frequency which takes into account electron collisions with SRR walls.
EAM Import::2019-03-13

Analytical formulation for the resonant frequency of split rings - Sydoruk, Oleksiy; Tatartschuk, Eugen; Shamonina, E.; Solymar, L. (Journal of Applied Physics, 2009)
A simple approximate expression is derived for the resonant frequency of a singly split single ring that is among the first microwave resonators designed to be small relative to the wavelength. In addition to the usual gap capacitance the concept of surface capacitance is introduced. The surface capacitance is determined analytically by two different methods, first using analytical expressions for the electric field of a split cylinder, and second by using conformal mapping. Taking two practical examples the resonant frequency, found analytically, is shown to agree with that obtained by numerical simulations. The model could be used for studies of the resonant properties of split rings in the terahertz region.
EAM Import::2019-03-13

Analytical model of the deformation-induced inertial dynamics of a magnetic vortex - Yoo, Myoung Woo; Mineo, Francesca; Kim, Joo Von (Journal of Applied Physics, 2021)
We present an analytical model to account for the deformation-induced inertial dynamics of a magnetic vortex. The model is based on a deformation of the vortex core profile based on the Döring kinetic field, whereby the deformation amplitudes are promoted to dynamical variables in a collective-coordinate approach that provides a natural extension to the Thiele model. This extended model describes complex transients due to inertial effects and the variation of the effective mass with velocity. The model also provides a quantitative description of the inertial dynamics leading up to vortex core reversal, which is analogous to the Walker transition in domain wall dynamics. Our work paves the way for a standard prescription for describing the inertial effects of topological magnetic solitons.
CRIS-Team Scopus Importer:2021-03-05

An efficient source of continuous variable polarization entanglement - Leuchs, Gerd; et al. (New Journal of Physics, 2007)
We have experimentally demonstrated the efficient creation of highly entangled bipartite continuous variable polarization states. Exploiting an optimized scheme for the production of squeezing using the Kerr non-linearity of a glass fibre we generated polarization squeezed pulses with a mean classical excitation in Ŝ3. Polarization entanglement was generated by interfering two independent polarization squeezed fields on a symmetric beam splitter. The resultant beams exhibit strong quantum noise correlations in the dark Ŝ1-Ŝ2 polarization plane. To verify entanglement generation, we characterized the quantum correlations of the system for two different sets of conjugate Stokes parameters. The quantum correlations along the squeezed and the anti-squeezed Stokes parameters were observed to be -4.1 ±0.3 and -2.6 ±0.3 dB below the shot noise level, respectively. The degree of correlations was found to depend critically on the beam-splitting ratio of the entangling beam splitter. Carrying out measurements on a different set of conjugate Stokes parameters, correlations of -3.6 ±0.3 and -3.4 ±0.3 dB have been observed. This result is more robust against asymmetries in the entangling beam splitter, even in the presence of excess noise. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.optik.1optik.aneffi

A new 4 pi geometry optimized for focusing on an atom with a dipole-like radiation pattern - Lindlein, Norbert; Maiwald, Robert; Konermann, Hildegard; Sondermann, Markus; Peschel, Ulf; Leuchs, Gerd (Laser Physics, 2007)
Focusing electromagnetic radiation efficiently onto an atom requires an open geometry, which is as close to the full solid angle as possible. Additionally, the radiant intensity should be as close as possible to a dipole radiation in order to have a similar field distribution as in the emission process. Here, we propose to make use of a novel combination of a parabolic mirror and a diffractive optical element. © 2007 MAIK "Nauka/ Interperiodica".
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.optik.1optik.anew4p

A new approach for modeling and smoothing of scattered 3D data - Häusler, Gerd; et al. (Proceedings of SPIE, 1998)
In order to digitize the whole surface of a three-dimensional object by means of an optical range sensor, usually multiple range images are acquired from different viewpoints and merged into a single surface description. The simplest and most accurate way is to generate a polyhedral surface. The data are usually distorted by measuring errors like noise, aliasing, outliers, calibration and registration errors, etc., so that they have to be filtered. Calibration and registration errors first appear after merging of different views. As the merged data are no longer represented on a grid, conventional filters for digital signal processing are not applicable. We introduce a new approach for modeling and smoothing scattered data based on an approximation of a mesh of circular arcs. This new method enables interpolation of curved surfaces using solely the vertex position and the associated vertex normals of a polyhedral mesh. The new smoothing filter is specifically adapted to the requirements of geometric data, as it minimizes curvature variations. In contrast to linear filters, undesired surface undulations are avoided, which is an important pre-condition for NC milling and rendering.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.anewap
Keywords: Geometric modeling; Reverse engineering; Scattered data interpolation; Scattered data modeling; Smoothing of polyhedral surfaces; Surface approximation; Surface interpolation; Surface reconstruction; Surface smoothing

A new method of short-coherence interferometry in human skin (in vivo) and in solid volume scatterers - Häusler, Gerd; et al. (SPIE j, 1996)
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.optik.1optik.anewme

A new method to reduce the spot size at a focused laser beam - Leuchs, Gerd; et al. (EOS Topical Meetings Digest, 2000)
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.optik.1optik.anewme

A Non-linear Subdivision Scheme for Triangle Meshes - Häusler, Gerd; et al. (Proc. of Vision, Modeling and Visualization 2000, 2000)
UnivIS-Import:2015-04-16:Pub.2000.nat.dphy.optik.1optik.anonli

An optical multimode fiber as pseudothermal light source - Mehringer, Thomas; Oppel, Steffen; von Zanthier, Joachim (Applied Physics B-Lasers and Optics, 2017)
We report on a novel pseudothermal light source based on laser light coupled into an optical multimode fiber. The setup is simple, low cost, exhibits inherently high directional light emission and allows for a flexible arrangement. By measuring the photon statistics and spatial two point intensity correlations in the far field we show that the setup exhibits all characteristics of a Gaussian random sourc

An optimized photon pair source for quantum circuits - Harder, Georg; Ansari, Vahid; Brecht, Benjamin; Dirmeier, Thomas; Marquardt, Christoph; Silberhorn, Christine (Optics Express, 2013)
We implement an ultrafast pulsed type-II parametric down conversion source in a periodically poled KTP waveguide at telecommunication wavelengths with almost identical properties between signal and idler. As such, our source resembles closely a pure, genuine single mode photon pair source with indistinguishable modes. We measure the joint spectral intensity distribution and second order correlation functions of the marginal beams and find with both methods very low effective mode numbers corresponding to a Schmidt number below 1.16. We further demonstrate the indistinguishability as well as the purity of signal and idler photons by Hong-Ou-Mandel interferences between signal and idler and between signal/idler and a coherent field, respectively. Without using narrowband spectral filtering, we achieve a visibility for the interference between signal and idler of 94.8% and determine a purity of more than 80% for the heralded single photon states. Moreover, we measure raw heralding efficiencies of 20.5% and 15.5% for the signal and idler beams corresponding to detector-loss corrected values of 80% and 70%. © 2013 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

A novel method for polarization squeezing with Photonic Crystal Fibers - Leuchs, Gerd; et al. (Optics Express, 2010)
Photonic Crystal Fibers can be tailored to increase the effective Kerr nonlinearity, while producing smaller amounts of excess noise compared to standard silicon fibers. Using these features of Photonic Crystal Fibers we create polarization squeezed states with increased purity compared to standard fiber squeezing experiments. Explicit we produce squeezed states in counter propagating pulses along the same fiber axis to achieve near identical dispersion properties. This enables the production of polarization squeezing through interference in a polarization type Sagnac interferometer. We observe Stokes parameter squeezing of -3.9 ± 0.3dB andanti-squeezingof 16.2 ±0.3dB. © 2010 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.optik.1optik.anovel

Anticaustics in a Fabry-Perot interferometer - Sanchez-Soto, Luis L.; Monzon, Juan J.; Leuchs, Gerd (Journal of the Optical Society of America A-Optics Image Science and Vision, 2022)
We address the response of a Fabry-Perot interferometer to a monochromatic point source. We calculate the anti -caustics (that is, the virtual wavefronts of null path difference) resulting from the successive internal reflections occurring in the system. They turn out to be a family of ellipsoids (or hyperboloids) of revolution, which allows us to reinterpret the operation of the Fabry-Perot interferometer from a geometrical point of view that facilitates comparison with other apparently disparate arrangements, such as Young's double slit. (c) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
CRIS-Team WoS Importer:2023-01-06

An ultrasmall mode volume cantilever-based Fabry-Pérot microcavity - Kelkar, Hrishikesh; Wang, Daqing; Hoffmann, Björn; Christiansen, Silke; Götzinger, Stephan; Sandoghdar, Vahid (CLEO: QELS - Fundamental Science, CLEO_QELS 2015, 2015)
A tunable Fabry-Pérot microcavity consisting of a 2.6 μm curvature mirror and 0.4 numerical aperture is fabricated. We study the effect of a nanoparticle on the cavity modes and discuss the coupling of single molecules. © OSA 2015.

Anwendung von Beam-Propagation-Method und Wave-Propagation-Method zur Simulation innovativ gedruckter Lichtwellenleiter - Backhaus, Carsten; Loosen, Florian; Vögl, Christian; Mansuroglu, Refik; Lindlein, Norbert (DGaO Proceedings 2018, 2018)
In der DFG-finanzierten Forschergruppe OPTAVER wurden Lichtwellenleiter mittels eines Aerosol-Druck-Verfahrens hergestellt. Eine dadurch ermöglichte Koppelstelle kann jedoch nicht mehr mittels Raytracing simuliert werden, da Interferenzeffekte nicht berücksichtigt werden. Eine Anwendung wellenoptischer Methoden auf die Problemstellung wird im Folgenden untersucht und dargestellt.<br
Keywords: Optische Systeme; Faseroptik; Optische Informationsübertragung

Approach for the production chain of printed polymer optical waveguides–an overview - Loosen, Florian; Backhaus, Carsten; Zeitler, Jochen Tobias; Hoffmann, Gerd-Albert; Reitberger, Thomas; Lorenz, Lukas; Lindlein, Norbert; Franke, Jörg; Overmeyer, Ludger; Suttmann, Oliver; Wolter, Klaus-Jürgen; Bock, Karlheinz (Applied Optics, 2017)
Research for new production chains in the field of waveguide fabrication is a challenging task. Realizing a cost efficient manufacturing process allows integrating optical data communication in arbitrary structures, for example, the wing of an airplane or the body of a car. The production chain described in this paper contains the design, simulation, and fabrication process of printed polymer optical waveguides (POWs).

A primary radiation standard based on quantum nonlinear optics - Lemieux, Samuel; Giese, Enno; Fickler, Robert; Chekhova, Maria; Boyd, Robert W. (Nature Physics, 2019)
The black body remains the most prominent source of light for absolute radiometry(1). Its main alternative, synchrotron radiation, requires costly and large facilities(2). Quantum optics offers a new radiometric source: parametric down-conversion (PDC), a nonlinear optical process, in which pairwise photon correlations enable absolute calibration of photodetectors(3-6). Since the emission rate crucially depends on the brightness of the electromagnetic field, quantum-mechanical fluctuations of the vacuum(7) can be seen as a seed of spontaneous PDC, and their amplitude is a natural radiometric standard. Thus, they allow for the calibration of the spectral radiance of light sources(8-11) by measuring the ratio between seeded and unseeded PDC. Here, we directly use the frequency spectrum of the electromagnetic vacuum to trigger spontaneous PDC and employ the generated light to infer the spectral response of a spectrometer over a broad spectral range. Then, we deduce the absolute quantum efficiency from the spectral shape of PDC in the high-gain regime, without relying on a seed or reference detector. Our results compare well with the ones obtained with a reference lamp, demonstrating a promising primary radiation standard.
CRIS-Team WoS Importer:2019-06-18

A pulsed source of continuous variable polarization entanglement - Leuchs, Gerd; et al. (Journal of Optics B Quantum and Semiclassical Optics, 2003)
We have experimentally demonstrated polarization entanglement using continuous variables in an ultra-short pulsed laser system at the telecommunications wavelength of 1.5 μm. Exploiting the Kerr non-linearity of a glass fibre we generated polarization squeezed pulses with Ŝ2 as the only non-zero Stokes parameter, thus Ŝ1 and Ŝ3 being the conjugate pair. Polarization entanglement was generated by interference of the polarization squeezed field with a vacuum on a 50:50 beamsplitter. The two resultant beams exhibit strong quantum noise correlations in Ŝ1 and Ŝ3. The sum noise signal of Ŝ3 was at the respective shot noise level and the difference noise signal of Ŝ1 fell -2.9 dB below this value.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.optik.1optik.apulse
Keywords: Continuous variables; Entanglement; Nonlinear optics; Polarization

A quantitative comparison of amplitude versus intensity interferometry for astronomy - Bojer, Manuel; Huang, Zixin; Karl, Sebastian; Richter, Stefan; Kok, Pieter; von Zanthier, Joachim (New Journal of Physics, 2022)
Astronomical imaging can be broadly classified into two types. The first type is amplitude interferometry, which includes conventional optical telescopes and very large baseline interferometry (VLBI). The second type is intensity interferometry, which relies on Hanbury Brown and Twiss-type measurements. At optical frequencies, where direct phase measurements are impossible, amplitude interferometry has an effective numerical aperture that is limited by the distance from which photons can coherently interfere. Intensity interferometry, on the other hand, correlates only photon fluxes and can thus support much larger numerical apertures, but suffers from a reduced signal due to the low average photon number per mode in thermal light. It has hitherto not been clear which method is superior under realistic conditions. Here, we give a comparative analysis of the performance of amplitude and intensity interferometry, and we relate this to the fundamental resolution limit that can be achieved in any physical measurement. Using the benchmark problem of determining the separation between two distant thermal point sources, e.g., two adjacent stars, we give a short tutorial on optimal estimation theory and apply it to stellar interferometry. We find that for very small angular separations the large baseline achievable in intensity interferometry can more than compensate for the reduced signal strength. We also explore options for practical implementations of very large baseline intensity interferometry (VLBII).
CRIS-Team WoS Importer:2022-04-29

A Robust Multiresolution Registration Approach - Häusler, Gerd; et al. (Proc. of Vision, Modeling and Visualization '99, 1999)
UnivIS-Import:2015-04-16:Pub.1999.nat.dphy.optik.1optik.arobus

A robust quantum receiver for phase shift keyed signals - Mueller, C. R.; Marquardt, Christoph (New Journal of Physics, 2015)
The impossibility of perfectly discriminating non-orthogonal quantum states imposes far-reaching consequences both on quantum and classical communication schemes. We propose and numerically analyze an optimized quantum receiver for the discrimination of phase encoded signals. Our scheme outperforms the standard quantum limit and approaches the Helstrom bound for any signal power. The discrimination is performed via an optimized, feedback-mediated displacement prior to a photon counting detector. We provide a detailed analysis of the influence of excess noise and technical imperfections on the average error probability. The results demonstrate the receiver's robustness and show that it can outperform any classical receiver over a wide range of realistic parameters.
CRIS-Team Scopus Importer:2022-06-05
Keywords: Coherent communication; Optical communication; Quantum information processing; Quantum noise; Quantum receiver

Arrayed free space continuous-wave terahertz photomixers - Bauerschmidt, Sebastian; Döhler, Gottfried; Lu, Hong; Gossard, Art; Malzer, Stefan; Preu, Sascha (Optics Letters, 2013)
We present free space coherent arrays of continuous-wave terahertz (THz) photomixers and compare the results to on-chip arrays. By altering the relative phases of the exciting laser signals, the relative THz phase between the array elements can be tuned, allowing for beam steering. In addition, the constructive interference of the emission of N elements leads to an increase of the focal intensity by a factor of N2 while reducing the beam width by ∼N-1, below the diffraction limit of a single source. Such array architectures strongly improve the THz power distribution for stand-off spectroscopy and imaging systems while providing a huge bandwidth at the same time. We demonstrate this by beam profiles generated by a 2 × 2 and a 4 × 1 array for a transmission distance of 4.2 m. Spectra between 70 GHz and 1.1 THz have been recorded with these arrays. © 2013 Optical Society of America.
Keywords: Terahertz emitter array; beam steering

Arrayed telecom-wavelength compatible THz n-i-pn-i-p superlattice photomixers for spectroscopy applications - Preu, Sascha; Bauerschmidt, Sebastian; Malzer, Stefan; Döhler, Gottfried; Lu, Hong; Gossard, Art; Wang, Lijun (Terahertz and Midinfrared Radiation, 2011)
We report on the progress of room-temperature operating, continuous-wave, tunable n-i-pn-i-p superlattice THz photomixers, compatible with 1.55μm telecom laser systems. An output power of 0.65μW at 1THz has been achieved at a photocurrent of 9.5mA, using a broadband antenna. The spectral power is at a level where high resolution spectroscopy becomes attractive. This is demonstrated by measuring the absorption spectrum of water vapor between 0.4 and 1.6THz. We constructed an array of 4 mutually coherent photomixers for higher output power and spatial resolution. The interference of the four individual beams was measured in the target plane at a stand-off distance of 4.2m. We report on both a small THz spot diameter along the array axis of<1cm for ν>0.3THz and a high intensity of the central interference peak, in excellent agreement with numerical simulations. These features are very attractive for stand-off imaging and spectroscopy. © 2011 Springer Science+Business Media B.V.

Arrays and new antenna topologies for increasing THz power generation using photomixers - Rivera-Lavado, Alejandro; Garcia-Munoz, Enrique; Döhler, Gottfried; Malzer, Stefan; Preu, Sascha; Bauerschmidt, Sebastian; Montero-De-Paz, J.; Ugarte-Munoz, E.; Andres-Garcia, Belen; Izquierdo-Bermudez, V.; Segovia-Vargas, Daniel (Journal of Infrared, Millimeter, and Terahertz Waves, 2013)
Power limitations in CW THz generation imposed by conventional photomixers ("antenna emitters", AEs) are the major drawbacks on THz generation. From the antenna point of view, two different strategies are proposed to increase the generated power: optimized arrays and lenses arrangements and the use of new dielectric horn antennas. Then, using multiple small lenses, one per each single element, instead of a large one, bigger than the array, makes the generated power much higher. In addition, horn antennas etched in the substrate are considered in order to reduce the energy distribution scattering. Finally, some manufacturing issues are discussed. © 2013 Springer Science+Business Media New York.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.LAP.arrays

Artiffcial wave plates made from subwavelength structures - Rothau, Sergej; Ghadyani, Zahra; Harder, Irina; Lindlein, Norbert (113. Jahrestagung der DGaO, 2012)

Aspherical surface testing by using spherical compensation - Lindlein, Norbert; et al. (Proceedings of SPIE, 1999)
A technique for testing aspherical surfaces without the use of a null-corrector is described. The wave-front sensor for the detection of the aspherical wave-front is a Shack-Hartmann sensor which has a significantly expanded range of measurable wave-front slopes. The optical testing set-up, the used algorithm for the dynamic range expansion, and experimental results are presented in this paper.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.optik.1optik.aspher

Assessing the polarization of a quantum field from stokes fluctuations - Klimov, A. B.; Bjoerk, G.; Soederholm, J.; Madsen, L. S.; Lassen, M.; Andersen, U. L.; Heersink, J.; Dong, Ruifang; Marquardt, Christoph; Leuchs, Gerd; Sanchez-Soto, L. L. (Physical Review Letters, 2010)
We propose an operational degree of polarization in terms of the variance of the Stokes vector minimized over all the directions of the Poincaré sphere. We examine the properties of this second-order definition and carry out its experimental determination. Quantum states with the same standard (first-order) degree of polarization are correctly discriminated by this new measure. We argue that a comprehensive quantum characterization of polarization properties requires a whole hierarchy of higher-order degrees. © 2010 The American Physical Society.
CRIS-Team Scopus Importer:2022-06-05

A Sub-Atomic Subdivision Approach - Häusler, Gerd; et al. (Proc. of Vision, Modeling and Visulaisation, 2001)
UnivIS-Import:2015-04-16:Pub.2001.nat.dphy.optik.1optik.asubat

A sub-λ3 mode volume cantilever-based Fabry-Pérot microcavity - Kelkar, Hrishikesh; Wang, Daqing; Hoffmann, Björn; Christiansen, Silke; Götzinger, Stephan; Sandoghdar, Vahid (Optics InfoBase Conference Papers, 2014)
CRIS-Team Scopus Importer:2023-03-07

Asymmetric broadcasting of quantum correlations - Jain, Aditya; Chakrabarty, Ndranil; Chatterjee, Sourav (Physical Review A, 2019)
In this work, we exhaustively investigate 1→2 local and nonlocal broadcasting of entanglement as well as correlations beyond entanglement (geometric discord) using asymmetric Pauli cloners with the most general two-qubit state as the resource. We exemplify asymmetric broadcasting of entanglement using "maximally entangled mixed states." We demonstrate the variation of broadcasting range with the amount of entanglement present in the resource state as well as with the asymmetry in the cloner. We show that it is impossible to optimally broadcast geometric discord with the help of these asymmetric Pauli cloning machines. We also study the problem of 1→3 broadcasting of entanglement using nonmaximally entangled state as the resource. For this task, we introduce a method we call successive broadcasting which involves application of 1→2 optimal cloning machines multiple times. We compare and contrast the performance of this method with the application of direct 1→3 optimal cloning machines. We show that 1→3 optimal cloner does a better job at broadcasting than the successive application of 1→2 cloners and the successive method can be beneficial in the absence of 1→3 cloners. We also bring out the fundamental difference between the tasks of cloning and broadcasting in the final part of the paper. We create examples to show that there exist local unitaries which can be employed to give a better range for broadcasting. Such unitary operations are not only economical, but also surpass the best possible range obtained using existing cloning machines enabling broadcasting of lesser entangled states. This result opens up a direction in exploration of methods to facilitate broadcasting which may outperform the standard strategies implemented through cloning transformations.
CRIS-Team Scopus Importer:2021-04-20

Asymptotic analysis of flow processes at drawing of single optical microfibres - Luzi, Giovanni; Epple, Philipp; Scharrer, Michael; Fujimoto Meinecke, Ken; Rauh, Cornelia; Delgado, Antonio (International Journal of Chemical Reactor Engineering, 2011)
Microstructured optical fibres (i.e. fibres that contain holes) have assumed a high profile in recent years, and given rise to many novel optical devices. The problem of manufacturing such fibres by heating and then drawing a preform is considered for both the cases of annular microfibres and annular capillaries. A fluid-mechanics model suggested in literature that uses asymptotic analysis based on the small aspect ratio of capillaries is analysed and revised. The leading-order equations are examined in some asymptotic limits, many of which give valuable practical information about the control parameters that influence the drawing process. Additionally, the solution obtained for a single capillary provides a suitable basis for describing more complicated fibre structures. Copyright © 2011 The Berkeley Electronic Press. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2011.tech.ITC.stmmec.asympt
Keywords: asymptotic analysis; holey fibre; microstructured optical fibres; numerical efforts; photonic crystal fibres

A telecentric line scanning system: requirements in the macroscopic and microscopic regime - Loosen, Florian; Lindlein, Norbert; Donner, Klaus (Proceeding, 116. DGaO-Jahrestagung, 2015)
Last year (lecture A28 - 115th DGaO annual meeting), we presented the concept of a compact and modular telecentric line scanning system, capable of measuring large surfaces, e.g. for deformation and scratch detection of aluminium rolled sheets. In this particular construction, a circular scan curve is imaged onto one line. Because of the modular design of the system, this system could be considered in an inline process as well. To be applicable either in macroscopic or microscopic regime, both single components (torus mirror and imaging system) as well as the complete system have to be configured accordingly. Using optical simulation tools, the characteristic parameters of the line scanner can be determined accurately. Due to field curvature and distortion, off-axis beams can distort the image on the detector (line camera) significantly. Therefore, a special interest was paid to the influence of the quality of the image points concerning the enlargement of the field angle and the imaging on the detector plane.
Keywords: Optisches Design; Optische Systeme; Messtechnik

Atmospheric channel characteristics for quantum communication with continuous polarization variables - Heim, Bettina; Elser, Dominique Alexander; Bartley, Tim; Sabuncu, Metin; Wittmann, Christoffer; Sych, Denis; Marquardt, Christoph; Leuchs, Gerd (Applied Physics B-Lasers and Optics, 2010)
We investigate the properties of an atmospheric channel for free space quantum communication with continuous polarization variables. In our prepare-and-measure setup, coherent polarization states are transmitted through an atmospheric quantum channel of 100 m length on the flat roof of our institute's building. The signal states are measured by homodyne detection with the help of a local oscillator (LO) which propagates in the same spatial mode as the signal, orthogonally polarized to it. Thus the interference of signal and LO is excellent and atmospheric fluctuations are auto-compensated. The LO also acts as a spatial and spectral filter, which allows for unrestrained daylight operation. Important characteristics for our system are atmospheric channel influences that could cause polarization, intensity and position excess noise. Therefore we study these influences in detail. Our results indicate that the channel is suitable for our quantum communication system in most weather condition
UnivIS-Import:2015-04-14:Pub.2010.nat.dphy.optik.1optik.atmosp

Atmospheric continuous-variable quantum communication - Heim, B.; Peuntinger, Christian; Killoran, N.; Khan, Imran; Wittmann, C.; Marquardt, Christoph; Leuchs, Gerd (New Journal of Physics, 2014)
We present a quantum communication experiment conducted over a point-to-point free-space link of 1.6 km in urban conditions. We study atmospheric influences on the capability of the link to act as a continuous-variable (CV) quantum channel. Continuous polarization states (that contain the signal encoding as well as a local oscillator (LO) in the same spatial mode) are prepared and sent over the link in a polarization multiplexed setting. Both signal and LO undergo the same atmospheric fluctuations. These are intrinsically auto-compensated which removes detrimental influences on the interferometric visibility. At the receiver, we measure the Q-function and interpret the data using the framework of effective entanglement (EE). We compare different state amplitudes and alphabets (two-state and four-state) and determine their optimal working points with respect to the distributed EE. Based on the high entanglement transmission rates achieved, our system indicates the high potential of atmospheric links in the field of CV quantum key distribution.
CRIS-Team Scopus Importer:2022-06-05
Keywords: atmospheric turbulence; polarization in atmospheric optics; quantum communication

Atomic mercury vapor inside a hollow-core photonic crystal fiber - Vogl, Ulrich; Peuntinger, Christian; Joly, Nicolas Y.; Russell, Philip St. J.; Marquardt, Christoph; Leuchs, Gerd (Optics Express, 2014)
We demonstrate high atomic mercury vapor pressure in a kagomé-style hollow-core photonic crystal fiber at room temperature. After a few days of exposure to mercury vapor the fiber is homogeneously filled and the optical depth achieved remains constant. With incoherent optical pumping from the ground state we achieve an optical depth of 114 at the 63P2 - 63D3 transition, corresponding to an atomic mercury number density of 6 × 1010cm-3. The use of mercury vapor in quasi one-dimensional confinement may be advantageous compared to chemically more active alkali vapor, while offering strong optical nonlinearities in the ultraviolet region of the optical spectrum.
CRIS-Team Scopus Importer:2022-06-05

Attacks on practical quantum key distribution systems (and how to prevent them) - Jain, Nitin; Stiller, Birgit; Khan, Imran; Elser, Dominique Alexander; Marquardt, Christoph; Leuchs, Gerd (Contemporary Physics, 2016)
With the emergence of an information society, the idea of protecting sensitive data is steadily gaining importance. Conventional encryption methods may not be sufficient to guarantee data protection in the future. Quantum key distribution (QKD) is an emerging technology that exploits fundamental physical properties to guarantee perfect security in theory. However, it is not easy to ensure in practice that the implementations of QKD systems are exactly in line with the theoretical specifications. Such theory–practice deviations can open loopholes and compromise security. Several such loopholes have been discovered and investigated in the last decade. These activities have motivated the proposal and implementation of appropriate countermeasures, thereby preventing future attacks and enhancing the practical security of QKD. This article introduces the so-called field of quantum hacking by summarising a variety of attacks and their prevention mechanisms.
CRIS-Team Scopus Importer:2021-06-29
Keywords: countermeasures; practical data security; quantum computer; Quantum cryptography; quantum hacking; quantum key distribution

Aufbereitung von 3D-Sensordaten für Reverse Engineering mit Slim3D - Häusler, Gerd; et al. (Optische 3D-Formerfassung, 1998)
UnivIS-Import:2015-04-16:Pub.1998.nat.dphy.optik.1optik.aufber

Automatic Coarse Registration of 3D Surface Data in Oral and Maxillofacial Surgery - Nkenke, Emeka; Neukam, Friedrich Wilhelm; Häusler, Gerd; et al. (Perspective in Image-Guided Surgery, Proceedings of the Scientific Workshop on Medical Robotics, Navigation and Visualizatiom, 2004)
UnivIS-Import:2015-04-16:Pub.2004.nat.dphy.optik.1optik.autima

Automatic registration method for multisensor datasets adopted for dimensional measurements on cutting tools - Shaw, Laura; Ettl, Svenja; Mehari, Fanuel; Weckenmann, Albert; Häusler, Gerd (Measurement Science & Technology, 2013)
Multisensor systems with optical 3D sensors are frequently employed to capture complete surface information by measuring workpieces from different views. During coarse and fine registration the resulting datasets are afterward transformed into one common coordinate system. Automatic fine registration methods are well established in dimensional metrology, whereas there is a deficit in automatic coarse registration methods. The advantage of a fully automatic registration procedure is twofold: it enables a fast and contact-free alignment and further a flexible application to datasets of any kind of optical 3D sensor. In this paper, an algorithm adapted for a robust automatic coarse registration is presented. The method was originally developed for the field of object reconstruction or localization. It is based on a segmentation of planes in the datasets to calculate the transformation parameters. The rotation is defined by the normals of three corresponding segmented planes of two overlapping datasets, while the translation is calculated via the intersection point of the segmented planes. First results have shown that the translation is strongly shape dependent: 3D data of objects with non-orthogonal planar flanks cannot be registered with the current method. In the novel supplement for the algorithm, the translation is additionally calculated via the distance between centroids of corresponding segmented planes, which results in more than one option for the transformation. A newly introduced measure considering the distance between the datasets after coarse registration evaluates the best possible transformation. Results of the robust automatic registration method are presented on the example of datasets taken from a cutting tool with a fringe-projection system and a focus-variation system. The successful application in dimensional metrology is proven with evaluations of shape parameters based on the registered datasets of a calibrated workpiece. © 2013 IOP Publishing Ltd.
UnivIS-Import:2015-04-14:Pub.2013.tech.FT.FT-QMFMT.automa
Keywords: automatic registration; cutting tools; three-dimensional metrology

Automatische Porenfindung in 3D-CT Daten - Häusler, Gerd; et al. (2001)
UnivIS-Import:2015-04-14:Pub.2001.forsch.gradui.gradui_6.automa

Automatische Segmentierung der Gewebegrenzen in 2D-Ultraschalldaten aus der Mund-Kiefer- und Gesichtschirurgie - Häusler, Gerd; Wittenberg, Thomas; Nkenke, Emeka; Ettl, Svenja; et al. (Informatik aktuell, 2006)
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.automa

Autonomous absolute calibration of an ICCD camera in single-photon detection regime - Qi, Luo; Just, Felix; Leuchs, Gerd; Chekhova, Maria V. (Optics Express, 2016)
Intensified charge coupled device (ICCD) cameras are widely used in various applications such as microscopy, astronomy, spectroscopy. Often they are used as single-photon detectors, with thresholding being an essential part of the readout. In this paper, we measure the quantum efficiency of an ICCD camera in the single-photon detection mode using the Klyshko absolute calibration technique. The quantum efficiency is obtained as a function of the threshold value and of the wavelength of the detected light. In addition, we study the homogeneity of the photon sensitivity over the camera chip area. The experiment is performed in the autonomous regime, without using any additional detectors. We therefore demonstrate the self-calibration of an ICCD camera.

A versatile source of single photons for quantum information processing - Förtsch, Michael; Fürst, Josef; Wittmann, Christoffer; Strekalov, Dmitry; Aiello, Andrea; Chekhova, Maria V.; Leuchs, Gerd; Silberhorn, Christine; Marquardt, Christoph (Nature Communications, 2013)
The generation of high-quality single-photon states with controllable narrow spectral bandwidths and central frequencies is key to facilitate efficient coupling of any atomic system to non-classical light fields. Such an interaction is essential in numerous experiments for fundamental science and applications in quantum communication and information processing, as well as in quantum metrology. Here we implement a fully tunable, narrow-band and efficient single-photon source based on a whispering gallery mode resonator. Our disk-shaped, monolithic and intrinsically stable resonator is made of lithium niobate and supports a cavity-assisted spontaneous parametric down-conversion process. The generated photon pairs are emitted into two highly tunable resonator modes. We verify wavelength tuning over 100 nm of both modes with controllable bandwidth between 7.2 and 13 MHz. Heralding of single photons yields anti-bunching with g (2) (0)<0.2. © 2013 Macmillan Publishers Limited. All rights reserved.
CRIS-Team Scopus Importer:2022-06-05

Axicon-type test interferometer for cylindrical surfaces: systematic error assessment - Lindlein, Norbert; et al. (Applied Optics, 1997)
The principle and the alignment aberration functions are described for an axicon-type test interferometer for measuring cylindrical mantle surfaces. Additionally, we show that the derived systematic alignment functions fulfill for reasonably small misalignments the requirements for measurements in the range of approximately 1/100 of a fringe. We verify this with optical path-length calculations, using ray tracing. © 1997 Optical Society of America.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.optik.1optik.axicon
Keywords: Alignment aberration functions; Axicon-type test interferometer; Cylinder test; Ray tracing

Balancing ballistic and hopping light transport by purposive arraying of colloidal particles - Romanov, Sergei G.; Orlov, Sergej; Vogel, Nicolas; Bley, Karina; Landfester, Katharina; Weiss, Clemens K.; Peschel, Ulf (Photonic Crystal Materials and Devices XI, 2014)
Keywords: 2-dimensional slab photonic crystal; Diffraction; Disorder; Etching; Mie resonance; Optical spectra; Photon hopping

Beeinflussung der optischen Eigenschaften von Polymer Optischen Wellenleitern durch das Druckpfad-Design - Backhaus, Carsten; Lindlein, Norbert; Zeitler, Jochen Tobias; Franke, Jörg (DGaO Proceedings, 2019)
In der DFG-finanzierten Forschergruppe OPTAVER (Optische Aufbau- und Verbindungstechnik für baugruppenintegrierte Bussysteme) wurden erfolgreich Lichtwellenleiter mittels eines Aerosol-Druck-Verfahrens mit vorheriger Konditionierung hergestellt sowie ein virtuelles Abbild der gesamten Prozesskette erstellt. Dieses Verfahren ermöglicht nahezu beliebige Druckpfade, sodass dies den Weg frei macht für neue Realisationen von optischen Buskopplungen.Ein nun möglicher Druckpfad ist jedoch nicht zwangsweise eine Verbesserung in Bezug auf die optischen Eigenschaften des Lichtwellenleiters. Die besondere Geometrie des Querschnitts der Polymer Optischen Wellenleiter (POW) beeinflusst das Design des Druckpfades. Ein Beispiel dafür ist der minimale Radius, den eine Kurve haben darf, damit kein Licht aus dem Wellenleiter auskoppelt. Um nun Vorschriften für das Druckpfad-Design ableiten zu können, benötigt es einer Charakterisierung der POWs bezüglich verschiedenster Druckpfade. Diese Charakterisierung wird vorgestellt und die daraus abgeleiteten Druckpfad-Design Vorschriften aufgezeigt. Des Weiteren werden neue Realisierungsmöglichkeiten von optischen Buskopplungen vorgestellt
Keywords: Additive Fertigung; Polymer Optische Wellenleiter; optische Eigenschaften

Benchmark for optical simulation tools in the european network of excellence on micro-optics NEMO - Lindlein, Norbert; et al. (Optical Design and Engineering II, 2005)
The European Network of Excellence on Micro-Optics (NEMO) is a consortium of about 30 European institutes and companies which are working on micro-optics. The network is supported by the European Commission for a period of four years. One of its work packages is the Centre for Modelling and Design consisting of about 20 partners. In this work package a benchmark of the capabilities of commercial and internal software tools which are available among the partners will be made. The ten test systems which are used for the benchmarking range from seemingly simple things like calculating the intensity distribution in the focus of a microlens to complete systems like for example an optical interconnect system with microlenses, DOEs and a prism. The paper will present some of the benchmark systems. First results of the benchmarking itself cannot be presented in this proceeding because the benchmarking just ends at the end of August (after the deadline of this proceeding). But, hopefully first results can be presented during the talk.
Keywords: Benchmarking; Micro-optics; Optical design tools; Ray tracing; Simulation; Wave-optical simulation

Binary Homodyne Detection for Observing Quadrature Squeezing in Satellite Links - Müller, Christian R.; Seshadreesan, Kaushik P.; Peuntinger, Christian; Marquardt, Christoph (2018 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2018, 2019)
Optical satellite links open up new prospects for realizing quantum physical experiments over unprecedented length scales. We demonstrate the feasibility of quadrature squeezing detection in satellite links using optical communication technology already in orbit. The detection process is complicated by the fact that the homo dyne detectors aboard of satellites often provide an efficient resolution of only one bit. We show experimentally, that despite this extremal constraint quantum squeezing can still be detected efficiently. The required sample overhead compared to an ideal homo dyne detector is only a factor of 3.3.
CRIS-Team Scopus Importer:2019-05-21

Binary homodyne detection for observing quadrature squeezing in satellite links - Müller, Christian; Seshadreesan, Kaushik P.; Peuntinger, Christian; Marquardt, Christoph (Physical Review Research, 2020)
Optical satellite links open up new prospects for realizing quantum physical experiments over unprecedented length scales. We analyze and affirm the feasibility of detecting quantum squeezing in an optical mode with homodyne detection of only one bit resolution, as is found in satellites already in orbit. We show experimentally that, in combination with a coherent displacement, a binary homodyne detector can still detect quantum squeezing efficiently even under high loss. The sample overhead in comparison to nondiscretized homodyne detection is merely a factor of 3.3.
CRIS-Team WoS Importer:2021-01-22

Birefringence and dispersion of cylindrically polarized modes in nanobore photonic crystal fiber - Euser, T. G.; Schmidt, M. A.; Joly, N. Y.; Gabriel, C.; Marquardt, Christoph; Zang, L. Y.; Foertsch, M.; Banzer, Peter; Brenn, A.; Elser, Dominique; Scharrer, Michael G; Leuchs, Gerd; et al. (Journal of the Optical Society of America B-Optical Physics, 2011)
We demonstrate experimentally and theoretically that a nanoscale hollow channel placed centrally in the solidglass core of a photonic crystal fiber strongly enhances the cylindrical birefringence (the modal index difference between radially and azimuthally polarized modes). Furthermore, it causes a large split in group velocity and group velocity dispersion. We show analytically that all three parameters can be varied over a wide range by tuning the diameters of the nanobore and the core.© 2010 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

Birth, death, and revival of spontaneous emission in a three-atom system - Mährlein, Simon; Götzendörfer, Lukas; Günthner, Kevin; Evers, Jorg; von Zanthier, Joachim (Physical Review Research, 2020)
Three identical two-level atoms in free space prepared in particular entangled single-photon excited states display a "birth," "death," and a nonperiodic "revival" of spontaneous emission in selected directions. Instead of recording the spontaneously emitted photon with a maximum probability at t = 0 as for a single atom, a "birth" manifests itself in an initially zero photon detection probability, increasing thereafter in particular directions. Alternatively, the photon detection probability decreases in particular directions from an initially maximal value to completely disappear ("death") and to reappear again ("revival"). We show how these phenomena can be induced in the fully excited system, by projecting the atomic ensemble into the required entangled single-photon excited state via detection of the first two spontaneously emitted photons. To observe death and revival of spontaneous emission it is necessary to provide both spatial and temporal interference for which a minimum of three atoms is required. Hereby, the third atom, located at a large distance with respect to the other two atoms, can be used to tune the time and direction of the death of the photon. From this manipulation of spontaneous decay at a distance, we anticipate multiple applications, in fundamental science as well as in quantum technologies.
CRIS-Team WoS Importer:2021-01-22

Bone tissue aging affects mineralization of cement lines - Milovanovic, Petar; Vom Scheidt, Annika; Mletzko, Kathrin; Sarau, George; Pueschel, Klaus; Djuric, Marija; Amling, Michael; Christiansen, Silke; Busse, Bjoern (Bone, 2018)
Cement lines are known as thin peripheral boundaries of the osteons. With a thickness below 5 μm their composition of inorganic and organic compounds has been a matter of debate. Here, we hypothesized that cement lines become hypermineralized and their degree of mineralization is not constant but related to the tissue age of the osteon. Therefore, we analyzed the calcium content of osteons and their corresponding cement lines in a range of different tissue ages reflected by osteonal mineralization levels in femoral cortical bone of both postmenopausal women with osteoporosis and bisphosphonate-treated cases. Quantitative backscattered electron imaging (qBEI) showed that cement lines are hypermineralized entities with consistently higher calcium content than their corresponding osteons (mean calcium content: 29.46 ± 0.80 vs. 26.62 ± 1.11 wt%; p < 0.001). Micro-Raman spectroscopy complemented the qBEI data by showing a significantly higher phosphate/amide I ratio in the cement lines compared to the osteonal bone (8.78 ± 0.66 vs. 6.33 ± 0.58, p < 0.001), which was both due to an increased phosphate peak and a reduced amide I peak in cement lines. A clear positive correlation of cement line mineralization and the mineralization of the osteon was observed (r = 0.839, p = 0.003). However, the magnitude of the difference between cement line and osteonal calcium content decreased with increased osteonal calcium content (r = −0.709, p < 0.001), suggesting diverging mineralization dynamics in these osseous entities. The number of mineralized osteocyte lacunae per osteon bone area correlated positively with both osteonal and cement line calcium content (p < 0.01). The degree of mineralization of cement lines may represent another tissue-age related phenomenon, given that it strongly relates to the osteonal mineralization level. Understanding of the cement lines' mineralization and their changes in aging and disease states is important for predicting crack propagation pathways and fracture resistance mechanisms in human cortical bone.
CRIS-Team Scopus Importer:2023-03-07
Keywords: Cement line; Mineralization; Mineralized osteocyte lacunae; Osteon; Osteoporosis

Bragg reflection and conversion between helical bloch modes in chiral three-core photonic crystal fiber - Loranger, Sebastien; Chen, Yang; Roth, Paul; Frosz, Michael H.; Wong, Gordon K. L.; Russell, Philip St. John (Journal of Lightwave Technology, 2020)
Optical fiber modes carrying orbital angular momentum (OAM) have many applications, for example in mode-division-multiplexing for optical communications. The natural guided modes of N-fold rotationally symmetric optical fibers, such as most photonic crystal fibers, are helical Bloch modes (HBMs). HBMs consist of a superposition of azimuthal harmonics (order m) of order A(m) = A(0) + mN. When such fibers are twisted, these modes become circularly and azimuthally birefringent, that is to say HBMs with equal and opposite values of A(0) and spin s are non-degenerate. In this article we report the use of Bragg mirrors to reflect and convert HBMs in a twisted three-core photonic crystal fiber, and show that by writing a tilted fiber Bragg grating (FBG), reflection between HBMs of different orders becomes possible, with high wavelength-selectivity. We measure the near-field phase and amplitude distribution of the reflected HBMs interferometrically, and demonstrate good agreement with theory. This new type of FBG has potential applications in fiber lasers, sensing, quantum optics, and in any situation where creation, conversion, and reflection of OAM-carrying modes is required.
CRIS-Team Scopus Importer:2020-09-18
Keywords: Fiber bragg gratings; helical bloch modes; orbital angular momentum; twisted fiber

Bragg reflection and conversion between helical Bloch modes in twisted three-core optical fiber - Loranger, Sébastien; Chen, Yang; Roth, Paul; Frosz, Michael H.; Ahmed, Goran; Wong, Gordon K.L.; Russell, Philip St. John (Frontiers in Optics - Proceedings Frontiers in Optics + Laser Science APS/DLS, 2019)
Fiber Bragg gratings are written for the first time into a three-fold rotationally symmetric twisted fiber with three cores, and the reflection of helical Bloch modes explored as the wavelength is tuned.
CRIS-Team Scopus Importer:2021-04-20

Bright EPR-entangled beams for quantum communication - Leuchs, Gerd; et al. (Quantum Communication, Measurement and Computing 3, 2001)
UnivIS-Import:2015-04-20:Pub.2001.nat.dphy.optik.1optik.bright

Broadband, Lensless, and Optomechanically Stabilized Coupling into Microfluidic Hollow-Core Photonic Crystal Fiber Using Glass Nanospike - Zeltner, Richard; Xie, Shangran; Pennetta, Riccardo; Russell, Philip St. John (ACS Photonics, 2017)
We report a novel technique for launching broadband laser light into liquid-filled hollow-core photonic crystal fiber (HC-PCF). It uniquely offers self-alignment and self-stabilization via optomechanical trapping of a fused silica nanospike, fabricated by thermally tapering and chemically etching a single mode fiber into a tip diameter of 350 nm. We show that a trapping laser, delivering ∼300 mW at 1064 nm, can be used to optically align and stably maintain the nanospike at the core center. Once this is done, a weak broadband supercontinuum signal (∼575–1064 nm) can be efficiently and close to achromatically launched in the HC-PCF. The system is robust against liquid-flow in either direction inside the HC-PCF, and the Fresnel back-reflections are reduced to negligible levels compared to free-space launching or butt-coupling. The results are of potential relevance for any application where the efficient delivery of broadband light into liquid-core waveguides is desired.
EAM Import::2019-03-13

Broadband mid-infrared supercontinuum generation in dispersion-engineered As2S3-silica nanospike waveguides pumped by 2.8 μm femtosecond laser - Wang, Pan; Huang, Jiapeng; Xie, Shangran; Troles, Johann; Russell, Philip St. John (Photonics Research, 2021)
Broadband mid-infrared (IR) supercontinuum laser sources are essential for spectroscopy in the molecular fingerprint region. Here, we report generation of octave-spanning and coherent mid-IR supercontinua in As2S3-silica nanospike hybrid waveguides pumped by a custom-built 2.8 μm femtosecond fiber laser. The waveguides are formed by pressure-assisted melt-filling of molten As2S3 into silica capillaries, allowing the dispersion and nonlinearity to be precisely tailored. Continuous coherent spectra spanning from 1.1 μm to 4.8 μm (30 dB level) are observed when the waveguide is designed so that 2.8 μm lies in the anomalous dispersion regime. Moreover, linearly tapered millimeter-scale As2S3-silica waveguides are fabricated and investigated for the first time, to the best of our knowledge, showing much broader supercontinua than uniform waveguides, with improved spectral coherence. The waveguides are demonstrated to be long-term stable and water-resistant due to the shielding of the As2S3 by the fused silica sheath. They offer an alternative route to generating broadband mid-IR supercontinua, with applications in frequency metrology and molecular spectroscopy, especially in humid and aqueous environments.
CRIS-Team Scopus Importer:2021-04-16

Broadband Omnidirectional Diversion of Light in Hybrid Plasmonic-Photonic Heterocrystals - Ding, Boyang; Bardosova, Maria; Pemble, Martyn E.; Korovin, Alexander V.; Peschel, Ulf; Romanov, Sergei G. (Advanced Functional Materials, 2011)
Broadband, omnidirectional, and polarization-independent diversion has been achieved of more than 90% of the light flow intensity off its incidence direction using hybrid metal–dielectric plasmonic-photonic heterocrystals. These architectures were prepared by depositing metal film on the interface between two photonic crystals of different parameters. The magnitude of light losses was extracted from angle-resolved measurements of transmission and reflectance spectra. Comparing these data for different stages of constructing the complex architecture, the diffraction in colloidal crystals, the excitation and radiative decay of short-living surface plasmon polaritons in a corrugated metal film and the eigenmode mismatch at the interface between two different photonic crystals were identified as corroborating physical mechanisms behind the light diversion.
EAM Import::2019-03-13

Broadband Operation of a Gain Switched TI:Sapphire Laser for Coherence Radar Measurements - Häusler, Gerd; et al. (Proceedings of SPIE, 1999)
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.optik.1optik.broadb

Broadband Optomechanically Stabilized Coupling to Liquid-Filled Hollow-Core Fiber Using Silica Nanospike - Zeltner, Richard; Xie, Shangran; Pennetta, Riccardo; Russell, Philip St. John (Optical Trapping Applications 2017, 2017)
An optomechanically self-aligned glass nanospike, fashioned from tapered single-mode fiber, is used to launch broadband light into liquid-filled hollow-core PCF. Stable, efficient and close to achromatic coupling is obtained over a 500 nm bandwidth.
EAM Import::2019-03-13

Broadcasting of entanglement via orthogonal and non-orthogonal state-dependent cloners - Shukla, Manish Kumar; Chakrabarty, Indranil; Chatterjee, Sourav (Quantum Information Processing, 2020)
In this work, we extensively study the problem of broadcasting of entanglement as state-dependent versus state-independent cloners. We start by re-conceptualizing the idea of state-dependent quantum cloning machine (SD-QCM), and in that process, we introduce different types of SD-QCMs, namely orthogonal and non-orthogonal cloners. We derive the conditions for which the fidelity of these cloners will become independent of the input state. We note that such a construction allows us to maximize the cloning fidelity at the cost of having partial information of the input state. In the discussion on broadcasting of entanglement, we start with a general two-qubit state as our resource and later we consider a specific example of Bell diagonal state. We apply both state-dependent and state-independent cloners (orthogonal and non-orthogonal), locally and non-locally, on input resource state and obtain a range for broadcasting of entanglement in terms of the input state parameters. Our results highlight several instances where the state-dependent cloners outperform their state-independent counterparts in broadcasting entanglement. Our study provides a comparative perspective on the broadcasting of entanglement via cloning in two-qubit scenario, when we have some knowledge of the resource ensemble versus a situation when we have no such information.
CRIS-Team Scopus Importer:2021-04-19
Keywords: Broadcasting; Cloning; Entanglement

Broadcasting of quantum correlations in qubit-qudit systems - Mundra, Rounak; Patel, Dhrumil; Chakrabarty, Indranil; Ganguly, Nirman; Chatterjee, Sourav (Physical Review A, 2019)
Quantum mechanical properties like entanglement, discord, and coherence act as fundamental resources in various quantum information processing tasks. Consequently, the technique of generating more resources from a few, typically termed as broadcasting, serves as a promising candidate for the design of quantum networks. One way to broadcast resources could be using a cloning operation. In this article, broadcasting of quantum resources beyond 2 - 2 systems is investigated. In particular, in 2 - 3 dimensions, a class of states not useful for broadcasting of entanglement is characterized considering an optimal universal Heisenberg cloning machine. The broadcasting ranges for maximally entangled mixed states and two-parameter class of states are obtained to exemplify our protocol. A significant derivative of our protocol is that the cloning operation generates a qutrit (3 - 3) entangled pair with positive partial transpose on one of the local sides, and an absolutely separable qubit (2 - 2) pair on the other side of the input bipartite 2 - 3-dimensional resource state. Moving beyond entanglement, in 2 - d dimensions, the impossibility to optimally broadcast quantum discord and quantum coherence (l1 norm) is established. However, some significant illustrations are provided to highlight that nonoptimal broadcasting of discord and coherence is still possible.
CRIS-Team Scopus Importer:2021-04-20

Broadening the high sensitivity range of squeezing-assisted interferometers by means of two-channel detection - Shukla, Gaurav; Salykina, Dariya; Frascella, Gaetano; Mishra, Devendra Kumar; Chekhova, Maria; Khalili, Farit Ya (Optics Express, 2021)
For a squeezing-enhanced linear (so-called SU(2)) interferometer, we theoretically investigate the possibility to broaden the phase range of sub-shot-noise sensitivity. We show that this goal can be achieved by implementing detection in both output ports, with the optimal combination of the detectors outputs. With this modification, the interferometer has the phase sensitivity independent of the interferometer operation point and, similar to the standard dark port regime, is not affected by the laser technical (excess) noise. Provided that each detector is preceded by a phase-sensitive amplifier, this sensitivity could be also tolerant to the detection loss.
CRIS-Team Scopus Importer:2021-01-29

Broadly tunable photon-pair generation in a suspended-core fiber - Hammer, Jonas; Chekhova, Maria; Häupl, Daniel; Pennetta, Riccardo; Joly, Nicolas (Physical Review Research, 2020)
Nowadays fiber biphoton sources are nearly as popular as crystal-based ones. They offer a single spatial mode and easy integrability into optical networks. However, fiber sources lack the broad tunability of crystals, which do not require a tunable pump. Here, we report a broadly tunable biphoton source based on a suspended core fiber. This is achieved by introducing pressurized gas into the fibers hollow channels, changing the step index. The mechanism circumvents the need for a tunable pump laser, making this a broadly tunable fiber biphoton source with a convenient tuning mechanism, comparable to crystals. We report a continuous shift of 0.30 THz/bar of the sidebands, using up to 25 bar of argon.
CRIS-Team WoS Importer:2021-01-15

Building and Controlling Superconducting Quantum Hardware towards Error-Corrected Quantum Computing - Eichler, Christopher (MQV Colloquium, 2022)
Keywords: wwwquantum

Building Superconducting Quantum Hardware towards Error-Corrected Quantum Computing - Eichler, Christopher (APS March Meeting: Quantum Computing Hardware, 2023)
Keywords: wwwquantum

Building Superconducting Quantum Hardware towards Error-Corrected Quantum Computing - Eichler, Christopher (2023)
Quantum Computers will ultimately rely on near-perfect logical gates, implemented while correcting errors at the physical level. The need for developing quantum hardware optimized for performing fast, repeatable, and high-fidelity syndrome measurements in quantum error-correcting codes such as the surface code therefore becomes increasingly important. In my talk, I will present advances in performing qubit readout and two-qubit gates in multi-qubit superconducting quantum processors, which enabled the recent experimental demonstration of repeated quantum error correction in surfaces codes. I will show how quantum processors optimized for quantum error correction can also serve as a testbed to explore noisy intermediate-scale quantum algorithms. The talk will conclude with a discussion about open challenges and opportunities to advance the speed and fidelity of syndrome detection in scalable device architectures by exploiting tunable coupling elements.
Keywords: wwwquantum

Building Superconducting Quantum Processors to exploreQuantum Error Correction and Quantum Neural Networks - Eichler, Christopher (Seminar hosted by Per Delsing, Chalmers University, 2021)
Keywords: wwwqudev

Buildup of post-recombination refractive index changes in krypton photoionized at high repetition rates - Köhler, Johannes; Köttig, Felix; Schade, Daniel; Tani, F.; Russell, P. St. J.; Russell, J. (Optics InfoBase Conference Papers, 2020)
The evolution of a recombination-driven density depression in a krypton-gas-filled capillary, photoionized at MHz repetition rates, is interferometrically tracked. The msec-long buildup increases in amplitude with pulse energy and repetition rate.
CRIS-Team Scopus Importer:2021-04-19

Bulk Er:Yb:glass soliton femtosecond laser - Leuchs, Gerd; et al. (CLEO Technical digest, 2001)
A bulk solid state Erbium glass laser used to generate ultrashort laser pulses in the femtosecond regime was presented using soliton dynamics. Intracavity self-phase modulation was used to achieve soliton mode-locking. The dependence of pulse shaping dynamics on the pump power and intracavity dispersion was investigated, and the results were compared with the soliton mode-locking model.
UnivIS-Import:2015-04-16:Pub.2001.nat.dphy.optik.1optik.bulker

Calibration for cylindrical specimens in grazing-incidence interferometry via integration of difference measurements. - Lindlein, Norbert; et al. (Applied Optics, 2006)
Cylindrical specimens may be tested advantageously by using grazing-incidence interferometry. A multiple positions test in combination with rotational averaging has recently been used to separate the surface deviations of the specimen from the interferometric aberrations. To reduce the measuring time and to check whether the results are reliable, a second procedure is now investigated, which uses the principle of the multiple positions test to determine quantities proportional to the difference quotients of the surface deviations. After numerical integration, the results can be compared with those obtained previously by rotational averaging. The measurement principle is described, and calibration results are presented.

Cascaded Phase-Preserving Amplitude Regeneration in a DPSK Transmission System - Schmauß, Bernhard; Stephan, Christian; Sponsel, Klaus; Onishchukov, Georgy; Leuchs, Gerd (ECOC 2009, Vienna, Austria, 20-24 September, 2009)
Experimental results obtained on 10 Gb/s RZ-DPSK transmission in a recirculating fiber-loop setup show that nonlinear amplifying loop mirrors can efficiently enhance system performance. Main limiting factor is amplified Rayleigh backscattering in highly nonlinear fiber. © VDE VERLAG GMBH.
UnivIS-Import:2017-12-18:Pub.2009.tech.IE.LEH.cascad

Cascaded phase-preserving multilevel amplitude regeneration - Röthlingshöfer, Tobias; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (Optics Express, 2014)
The performance of cascaded in-line phase-preserving amplitude regeneration using nonlinear amplifying loop mirrors has been studied in numerical simulations. As an example of a spectrally efficient modulation format with two amplitude states and multiple phase states, the regeneration performance of a star-16QAM format, basically an 8PSK format with two amplitude levels, was evaluated. An increased robustness against amplified spontaneous emission and nonlinear phase noise was observed resulting in a significantly increased transmission distance.
lhft_intern.bib::Roethlingshoefer2014_4

Cavity optomechanics in a levitated helium drop - Childress, Lilian; Schmidt, M. P.; Kashkanova, A. D.; Brown, C. D.; Harris, G. I.; Aiello, Andrea; Marquardt, Florian; Harris, J. G. E. (Physical Review A, 2017)
We describe a proposal for a type of optomechanical system based on a drop of liquid helium that is magnetically levitated in vacuum. In the proposed device, the drop would serve three roles: its optical whispering-gallery modes would provide the optical cavity, its surface vibrations would constitute the mechanical element, and evaporation of He atoms from its surface would provide continuous refrigeration. We analyze the feasibility of such a system in light of previous experimental demonstrations of its essential components: magnetic levitation of mm-scale and cm-scale drops of liquid He, evaporative cooling of He droplets in vacuum, and coupling to high-quality optical whispering-gallery modes in a wide range of liquids. We find that the combination of these features could result in a device that approaches the single-photon strong-coupling regime, due to the high optical quality factors attainable at low temperatures. Moreover, the system offers a unique opportunity to use optical techniques to study the motion of a superfluid that is freely levitating in vacuum (in the case of He4). Alternatively, for a normal fluid drop of He3, we propose to exploit the coupling between the drop's rotations and vibrations to perform quantum nondemolition measurements of angular momentum.
CRIS-Team Scopus Importer:2023-03-27

CEP-stable generation of close to single-cycle and ultrashort UV pulses at 800 kHz repetition rate using a gas-filled hollow-core PCF - Ermolov, Alexey; Heide, Christian; Dienstbier, Philip; Tani, Francesco; Köttig, Felix; Hommelhoff, Peter; Russell, Philip St. John (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Ultrashort laser pulses at high repetition rates are a fundamental tool in a wide range of applications in strong-field physics and attosecond science, where particular attention has to be given to the stability of the carrier to envelope phase (CEP) of the ultrashort optical waveform [1]. Here we report the generation of close to single-cycle pulses with stable CEP at 800 kHz repetition rate, obtained via soliton-effect self-compression in a gas-filled kagomé-type hollow-core photonic crystal fibre (kagomé-PCF) [2]. In addition, we have measured for the first time the CEP stability of soliton-emitted dispersive waves (DWs) lying in the ultraviolet spectral region.
CRIS-Team Scopus Importer:2019-11-15

Characteristics of the Diffuse Astrophysical Electron and Tau Neutrino Flux with Six Years of IceCube High Energy Cascade Data - Aartsen, M. G.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Alispach, C.; Andeen, K.; Anderson, T.; Ansseau,; Anton, Gisela; Arguelles, C.; et al. (Physical Review Letters, 2020)
We report on the first measurement of the astrophysical neutrino flux using particle showers (cascades) in IceCube data from 2010-2015. Assuming standard oscillations, the astrophysical neutrinos in this dedicated cascade sample are dominated (similar to 90%) by electron and tau flavors. The flux, observed in the sensitive energy range from 16 TeV to 2.6 PeV, is consistent with a single power-law model as expected from Fermi-type acceleration of high energy particles at astrophysical sources. We find the flux spectral index to be gamma = 2.53 +/- 0.07 and a flux normalization for each neutrino flavor of phi(astro) = 1.66(-0.27)(+0.25) at E-0 = 100 TeV, in agreement with IceCube's complementary muon neutrino results and with all-neutrino flavor fit results. In the measured energy range we reject spectral indices gamma <= 2.28 at >= 3 sigma significance level. Because of high neutrino energy resolution and low atmospheric neutrino backgrounds, this analysis provides the most detailed characterization of the neutrino flux at energies below similar to 100 TeV compared to previous IceCube results. Results from fits assuming more complex neutrino flux models suggest a flux softening at high energies and a flux hardening at low energies (p value >= 0.06). The sizable and smooth flux measured below similar to 100 TeV remains a puzzle. In order to not violate the isotropic diffuse gamma-ray background as measured by the Fermi Large Area Telescope, it suggests the existence of astrophysical neutrino sources characterized by dense environments which are opaque to gamma rays.
CRIS-Team WoS Importer:2020-10-02

Characterization and application of continuous variable quantum states of light - Marquardt, Christoph (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2007)
The aim of this thesis was the characterization of continuous variable quantum states of light and their application in quantum information processing protocols. The photo current statistics of squeezed and entangled states from a nonlinear fiber Sagnac interferometer were analyzed and can be regarded as Gaussian states within the measurement accuracy. In addition, instead of the usual variance, the covariance was experimentally investigated as a relative measure of squeezing, using a balanced self-homodyne system. As an application in a quantum information protocol the experimental distillation of squeezed states has been shown. The undistilled squeezed states suffered from non-Gaussian classical excess noise. In the experiment nearly the complete squeezing could be recovered by a probabilistic selection method. The Cavalcanti-Reid criterion to prove intrinsic macroscopic superposition states in continuous variables was experimentally applied for the first time. With this criterion generalized superposition states were proven in vacuum and intense coherent states with a distance in phase space of 0.51+/-0.02 shot noise units. For squeezed states from an optical parametric oscillator generalized superposition states were proven with a distance of up to 0.83+/-0.02 shot noise units. At the same time the dependence of the criterion on squeezing and purity of the states was investigated. To reconstruct the quantum state of the polarization variables of light, a theory was developed, that is based on the su(2) algebra and at the same time takes into account the possibility, that the photon number is not fixed. It was found that for high photon numbers the quantum state reconstruction of the SU(2) Q function in Poincare space is an inverse 3D Radon transformation. With this method the Q function of a polarization squeezed state was reconstructed from measured data. In the dark plane of a polarization squeezed state the Wigner function of an intense Kerr squeezed state was reconstructed for the first time.<br
Keywords: quantum state reconstruction; quantum state distillation; photon statistics; Squeezed state

Characterization of cylindrical lenses with the help of grazing incidence interferometry for micro- and macro-optics - Lindlein, Norbert; et al. (19th Congress of the International Commisssion for Optics Optics for the Quality of Life, 2003)
The cylinder geometry allows for grazing incidence tests of optical surfaces let it be micro- or macro cylinder lenses. By using diffiactive beam splitter and beam shaping elements a grazing incidence interferometer can be built where the zero diffraction order is used as reference beam and one of the first orders as probe beam for the cylinder surface. Circular as well as noncircular meridian curves can be dealt with by shaping the DOE structure accordingly. The structure of the DOE are parallel curves to the meridian providing a constant spatial frequency which alleviates the lithographic process. The fringes indicate surface deviations from fringe to fringe by p/2 where p is the pitch of the DOE. A description of a micro- and a macro-interferometer together with measuring results will be given.
Keywords: Computer generated holograms; Grazing incidence interferometry; Micro-optics; Optical Physics

Characterization of cylindrical micro-lenses in transmitted light and with grazing incidence interferometry in reflected light - Lindlein, Norbert; et al. (Optical Micro- and Nanometrology in Microsystems Technology, 2006)
High numerical aperture cylindrical micro-lenses are needed in collimating the laser light from laser bars in the near infrared. Diffraction limited performance of such collimation lenses can only be obtained if the surface shape deviates strongly from circular symmetry. Therefore, null tests make the use of diffractive optical elements (DOE) necessary. For performance test at the design wavelength the reference DOE produces an ideal cylinder wave which enables the compensation of the wave front coming from the micro-lens to a plane wave. The use of a DOE-master enables beside the null test geometry also a removal of the anamorphic distortion due to the cylinder geometry. The DOEs having a numerical aperture of 0.8 are produced on an e-beam machine. The measurement of the wave aberrations is done with the help of the phase shifting technique. Alignment aberrations are eliminated by a least square fit of suitable misalignment functionals derived from an analytic approximation. The shape of the micro-lenses is tested in reflected light showing surface defects directly. The cylinder symmetry allows for a grazing incidence test using two DOE with nearly constant spatial frequency. There are no limitations concerning the test of high numerical aperture surfaces since the structure of the diffractive elements are parallel curves to the profile curve. The mean spatial frequency of the DOE defines the effective wavelength. Since we use a diffractive interferometer the effective wavelength is identical to the pitch of the DOE. Usually pitches between 4-10 μm are used resulting in a fringe sensitivity of 2-5 μm. The test delivers the deviation of the surface from the ideal form. In the case of non-circular symmetry the DOE deviates from the axicon type DOE. In addition to the shape deviations also the radius of curvature at the vertex can be measured. The stage for the cylindrical micro-lens is equipped with a length measuring device using grating references from Renishaw providing a length increment of 0.1 μm. With the axicon DOE there are two positions where nearly fluffed out fringes can be observed. Starting from the basic test position the lens can be moved until the vertex of the lens coincides with the focal line of the wave generated by the central part of the DOE. The distance between these two positions gives the radius of curvature for the vertex. Modern manufacturing of micro-lenses comprises also hot embossing in plastics or even into glass. Because of the small dimensions of the lenses and the required accuracy of the surface shape also tests of the impressing mould have to be carried out. The DOE approach enables also the test of the embossing form with the same sensitivity as the final test of the lens. Measuring results for the two test methods will be given.
Keywords: Cylindrical micro lens; Diffractive optics; Grazing incidence; Null test; Phase shifting interferometry

Characterization of microlenses using a phase-shifting shearing interferometer - Lindlein, Norbert; et al. (Optical Engineering, 1994)
A shearing interferometer is proposed for the characterization of microlenses. The optical configuration of the test system enables the measurement of the wave aberrations, the focal length, and the deviations of the lens surface from an ideal sphere. In addition, a quantitative evaluation method is given that enables the calculation of the wave aberrations (e.g., the phase function) from the shearing interferometer data.
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.optik.1optik.charac

Characterization of microoptical components - Lindlein, Norbert (2003 Conference on Lasers and Electro-Optics Europe, CLEO/EUROPE 2003, 2003)
Microoptical components are more and more important in technical applications due to the miniaturization of optical systems for communication, sensors, visualization devices and other purposes. Since the quality in the fabrication of an optical element cannot be better than the measurement accuracy with which the element can be tested, it is very important that also microoptical components can be characterized with sufficient accuracy. In this paper several measurement devices for microoptical components like rotationally symmetric microlenses and cylindrical microlenses will be presented. © 2003 IEEE.

Characterization of sub-wavelength structures usingphase-singularities - Leuchs, Gerd; et al. (Proc. Vol. XV,Industrial Systems: Part II, 2001)
UnivIS-Import:2015-04-16:Pub.2001.nat.dphy.optik.1optik.charac

Chemical and (Photo)-Catalytical Transformations in Photonic Crystal Fibers - Schmidt, Matthias; Cubillas, Ana Maria; Taccardi, Nicola; Euser, Tijmen; Cremer, Till; Maier, Florian; Steinrück, Hans-Peter; Russell, Philip St. John; Wasserscheid, Peter; Etzold, Bastian (ChemCatChem, 2013)
The concept of employing photonic crystal fibers for chemical and (photo)-catalytical transformations is presented. These optofluidic microdevices represent a versatile platform where light and fluids can interact for spectroscopic or photoactivation purposes. The use of photonic crystal fibers in chemistry and sensing is reviewed and recent applications as catalytic microreactors are presented. Results on homogeneous catalysis and the immobilization of homogeneous and heterogeneous catalysts in the fiber channels are discussed. The examples demonstrate that combining catalysis and the excellent light guidance of photonic crystal fibers provides unique features for example, for photocatalytic activation and quantitative photospectroscopic reaction analysis. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral optical response of planar and symmetric nanotrimers enabled by heteromaterial selection - Banzer, Peter; Wozniak, Pawel; Mick, Uwe; De Leon, Israel; Boyd, Robert W. (Nature Communications, 2016)
Chirality is an intriguing property of certain molecules, materials or artificial nanostructures, which allows them to interact with the spin angular momentum of the impinging light field. Due to their chiral geometry, they can distinguish between left-and right-hand circular polarization states or convert them into each other. Here we introduce an approach towards optical chirality, which is observed in individual two-dimensional and geometrically mirror-symmetric nanostructures. In this scheme, the chiral optical response is induced by the chosen heterogeneous material composition of a particle assembly and the corresponding resonance behaviour of the constituents it is built from, which breaks the symmetry of the system. As a proof of principle, we investigate such a structure composed of individual silicon and gold nanoparticles both experimentally, as well as numerically. Our proposed concept constitutes an approach for designing two-dimensional chiral media tailored at the nanoscale, allowing for high tunability of their optical response.

Classical and quantum properties of cylindrically polarized beams of light via a poincaré sphere representation - Holleczek, A.; Aiello, A.; Gabriel, C.; Marquardt, Christoph; Leuchs, Gerd (Optics InfoBase Conference Papers, 2011)
CRIS-Team Scopus Importer:2022-06-05

Classical and quantum properties of cylindrically polarized states of light - Holleczek, Annemarie; Aiello, Andrea; Gabriel, Christian; Marquardt, Christoph; Leuchs, Gerd (Optics Express, 2011)
We investigate theoretical properties of beams of light with non-uniform polarization patterns. Specifically, we determine all possible configurations of cylindrically polarized modes (CPMs) of the electromagnetic field, calculate their total angular momentum and highlight the subtleties of their structure. Furthermore, a hybrid spatio-polarization description for such modes is introduced and developed. In particular, two independent Poincaré spheres have been introduced to represent simultaneously the polarization and spatial degree of freedom of CPMs. Possible mode-to-mode transformations accomplishable with the help of Bconventional polarization and spatial phase retarders are shown within this representation. Moreover, the importance of these CPMs in the quantum optics domain due to their classical features is highlighted. © 2011 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

Classical entanglement in polarization metrology - Toeppel, Falk; Aiello, Andrea; Marquardt, Christoph; Giacobino, Elisabeth; Leuchs, Gerd (New Journal of Physics, 2014)
Quantum approaches relying on entangled photons have been recently proposed to increase the efficiency of optical measurements. We demonstrate here that, surprisingly, the use of classical light with entangled degrees of freedom can also bring outstanding advantages over conventional measurements in polarization metrology. Specifically, we show that radially polarized beams of light allow to perform real-time single-shot Mueller matrix polarimetry. Our results also indicate that quantum optical procedures requiring entanglement without nonlocality can be actually achieved in the classical optics regime. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
CRIS-Team Scopus Importer:2022-06-05
Keywords: applied classical electromagnetism; entanglement and quantum nonlocality; polarization

Classical entanglement: Theory and application - Töppel, F.; Aiello, A.; Marquardt, Christoph; Giacobino, E.; Leuchs, Gerd (Optics InfoBase Conference Papers, 2015)
CRIS-Team Scopus Importer:2022-06-05

Classically entangled optical beams for high-speed kinematic sensing - Berg-Johansen, Stefan; Töppel, Falk; Stiller, Birgit; Banzer, Peter; Ornigotti, Marco; Giacobino, Elisabeth; Leuchs, Gerd; Aiello, Andrea; Marquardt, Christoph (Optica, 2015)
Tracking the kinematics of fast-moving objects is an important diagnostic tool for science and engineering. Here, we demonstrate an approach to positional and directional sensing based on the concept of classical entanglement in vector beams of light [Found. Phys. 28, 361–374 (1998)]. The measurement principle relies on the intrinsic correlations existing in such beams between transverse spatial modes and polarization. The latter can be determined from intensity measurements with only a few fast photodiodes, greatly outperforming the bandwidth of current CCD/CMOS devices. In this way, our setup enables two-dimensional real-time sensing with temporal resolution in the GHz range. We expect the concept to open up new directions in metrology and sensing.
CRIS-Team Scopus Importer:2021-06-29
Keywords: Classical and quantum physics; Optical sensing and sensors

Classical model of spontaneous parametric down-conversion - Kulkarni, Girish; Rioux, Jeremy; Braverman, Boris; Chekhova, Maria; Boyd, Robert W. (Physical Review Research, 2022)
We model spontaneous parametric down-conversion (SPDC) as classical difference frequency generation (DFG) of the pump field and a hypothetical stochastic "vacuum" seed field. We analytically show that the second-order spatiotemporal correlations of the field generated from the DFG process replicate those of the signal field from SPDC. Specifically, for low gain, the model is consistent with the quantum calculation of the signal photon's reduced density matrix; and for high gain, the model's predictions are in good agreement with our experimental measurements of the far-field intensity profile, orbital angular momentum spectrum, and wavelength spectrum of the SPDC field for increasing pump strengths. We further theoretically show that the model successfully captures second-order SU(1,1) interference and induced coherence effects in both gain regimes. Intriguingly, the model also correctly predicts the linear scaling of the interference visibility with object transmittance in the low-gain regime-a feature that is often regarded as a quintessential signature of the nonclassicality of induced coherence. Our model may not only lead to fundamental insights into the classical-quantum divide in the context of SPDC and induced coherence, but can also be a useful theoretical tool for numerous experiments and applications based on SPDC.
CRIS-Team WoS Importer:2022-08-19

Cluster state generation with quadrature squeezed cylindrically polarized modes - Gabriel, Christian; Rigas, Ioannes; Aiello, Andrea; Berg-Johansen, Stefan; van Loock, Peter; Marquardt, Christoph; Leuchs, Gerd (2012 Conference on Lasers and Electro-Optics, CLEO 2012, 2012)
We present schemes which exploit the hybrid-entanglement in quadrature squeezed cylindrically polarized modes to generate cluster states. Such states are essential for one-way quantum computing. © 2012 OSA.
CRIS-Team Scopus Importer:2022-06-05

Coherence Radar and Spectral Radar - New Tools for Dermatological Diagnosis - Häusler, Gerd; et al. (Journal of Biomedical Optics, 1998)
"Coherence radar," an optical 3-D sensor based on short coherence interferometry, is used to measure skin surface topology. This method is called optical coherence profilometry (OCP) and it may be a useful tool for medical diagnosis in dermatology because different medical conditions show distinct alterations of the skin surface. The measuring uncertainty is less than 2 μm. The measuring time is about 4 s. in vivo 3-D mapping of naked skin was performed without preparation. For clinical application, a fiber optical implementation was introduced. Spectral radar is an optical sensor for the acquisition of skin morphology based on OCT techniques. The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. The theory of the sensor, including the dynamic range, is discussed and in vivo measurements of human skin by a fiber optical implementation of the sensor are demonstrated. © 1998 Society of Photo-Optical Instrumentation Engineer
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.cohere
Keywords: Coherence radar; Fourier spectroscopy; Human skin; In vivo measurements; Melanoma maligna; Optical coherence profilometry; Optical coherence tomography; Speckle interferometry; Spectral radar; Volume scatterers

'Coherence Radar' - New Modifications of White Light Interferometry for Large Objects Shape Acquisition - Häusler, Gerd; et al. (Proc. of the EOS Topical Meeting on Optoelectronics Distance Measurements and Applications, 1997)
UnivIS-Import:2015-04-16:Pub.1997.nat.dphy.optik.1optik.cohere

"Coherence Radar, Spectral Radar, Dispersion Radar": Modifications of Broad Band Interferometry for High Accuracy 3D-Measurements in Medicine and Industry - Häusler, Gerd; et al. (Proc. of ODIMAP II, 1999)
UnivIS-Import:2015-04-16:Pub.1999.nat.dphy.optik.1optik.cohere

Coherent Conversion Between Microwave and Optical Photons-An Overview of Physical Implementations - Lambert, Nicholas J.; Rueda, Alfredo; Sedlmeir, Florian; Schwefel, Harald G. L. (Advanced Quantum Technologies, 2020)
Quantum information technology based on solid state qubits has created much interest in converting quantum states from the microwave to the optical domain. Optical photons, unlike microwave photons, can be transmitted by fiber, making them suitable for long distance quantum communication. Moreover, the optical domain offers access to a large set of very well-developed quantum optical tools, such as highly efficient single-photon detectors and long-lived quantum memories. For a high fidelity microwave to optical transducer, efficient conversion at single photon level and low added noise is needed. Currently, the most promising approaches to build such systems are based on second-order nonlinear phenomena such as optomechanical and electro-optic interactions. Alternative approaches, although not yet as efficient, include magneto-optical coupling and schemes based on isolated quantum systems like atoms, ions, or quantum dots. Herein, the necessary theoretical foundations for the most important microwave-to-optical conversion experiments are provided, their implementations are described, and the current limitations and future prospects are discussed.
CRIS-Team WoS Importer:2020-07-31

Coherent coupling of single molecules to a chip-based optical circuit - Rattenbacher, Dominik; Shkarin, Alexey; Renger, Jan; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (Optics InfoBase Conference Papers, 2019)
We present the coherent coupling of single dye molecules to subwavelength waveguides (nanoguides) and microresonators made of TiO2 on a chip. Integrated electrodes allow us to tune several molecules into resonance via the Stark effect.
CRIS-Team Scopus Importer:2019-07-09

Coherent coupling of single molecules to microresonators - Shkarin, Alexey; Rattenbacher, Dominik; Renger, Jan; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Many interesting proposals in quantum optics and light-matter interaction rely on having multiple quantum emitters well-coupled to a single mode of light. Of particular interest are cases where several identical emitters couple to a one-dimensional (1D) photonic medium. Recently, we presented such a system by evanescent coupling of organic dye molecules to the same guided mode of an on-chip subwavelength waveguide [1]. While this coupling allowed us to demonstrate up to 7.5% transmission extinction of the propagating light by a single molecule, it is still not sufficient for achieving higher-order effects such as photon-mediated interaction of multiple emitters coupled to the same waveguide.
CRIS-Team Scopus Importer:2019-11-15

Coherent coupling of single molecules to on-chip ring resonators - Rattenbacher, Dominik; Shkarin, Alexey; Renger, Jan; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (New Journal of Physics, 2019)
We report on cryogenic coupling of organic molecules to ring microresonators obtained by looping subwavelength waveguides (nanoguides). We discuss fabrication and characterization of the chip-based nanophotonic elements which yield a resonator finesse in the order of 20 when covered by molecular crystals. Our observed extinction dips from single molecules reach 22%, consistent with an expected enhancement factor of up to 11 for the molecular emission into the nanoguide. Future efforts will aim at efficient coupling of a handful of molecules via their interaction with a ring microresonator mode, setting the ground for the realization of quantum optical cooperative effects.
CRIS-Team WoS Importer:2019-07-19

Coherent interaction of light with a single molecule and a plasmonic nanoparticle - Zirkelbach, Johannes; Türschmann, Pierre; Renger, Jan; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (Optics InfoBase Conference Papers, 2019)
We demonstrate partial cloaking of a gold nanoparticle by a single organic molecule as a result of their coherent interaction with a monochromatic laser beam at cryogenic temperatures. Spectral and fluorescence lifetime analyses are presented.
CRIS-Team Scopus Importer:2019-07-09

Coherent nonlinear optics of quantum emitters in nanophotonic waveguides - Türschmann, Pierre; Le Jeannic, Hanna; Simonsen, Signe F.; Haakh, Harald R.; Götzinger, Stephan; Sandoghdar, Vahid; Lodahl, Peter; Rotenberg, Nir (Nanophotonics, 2019)
Coherent quantum optics, where the phase of a photon is not scrambled as it interacts with an emitter, lies at the heart of many quantum optical effects and emerging technologies. Solid-state emitters coupled to nanophotonic waveguides are a promising platform for quantum devices, as this element can be integrated into complex photonic chips. Yet, preserving the full coherence properties of the coupled emitter-waveguide system is challenging because of the complex and dynamic electromagnetic landscape found in the solid state. Here, we review progress toward coherent light-matter interactions with solid-state quantum emitters coupled to nanophotonic waveguides. We first lay down the theoretical foundation for coherent and nonlinear light-matter interactions of a two-level system in a quasi-one-dimensional system, and then benchmark experimental realizations. We discuss higher order nonlinearities that arise as a result of the addition of photons of different frequencies, more complex energy level schemes of the emitters, and the coupling of multiple emitters via a shared photonic mode. Throughout, we highlight protocols for applications and novel effects that are based on these coherent interactions, the steps taken toward their realization, and the challenges that remain to be overcome.
CRIS-Team Scopus Importer:2019-09-24
Keywords: nonlinear optics; quantum photonics; solid-state emitters; waveguides

Collecting and Manipulating Single Photons with Near-Unity Efficiency - Götzinger, Stephan (2020 European Conference on Optical Communications, ECOC 2020, 2020)
In this tutorial I will first review various approaches which have been employed to efficiently collect single photons from a single emitter. In the second part I will discuss experiments where a single molecule provides an optical nonlinearity strong enough to manipulate single photons.
CRIS-Team Scopus Importer:2021-04-19

Collecting more than half the fluorescence photons from a single ion - Maiwald, Robert; Golla, Andrea; Fischer, Martin; Bader, Marianne; Heugel, Simon Tobias; Chalopin, Benoit; Sondermann, Markus; Leuchs, Gerd (Physical Review A, 2012)
We demonstrate the trapping of a single ion in the focus of a deep parabolic mirror that covers 81% of the solid angle surrounding the ion. Accounting for the reflectivity of the mirror we infer a photon collection efficiency of 54.8% for our setup. The underlying experimentally detected maximum fluorescence rate is 1.91×106 s 1 from a single 174Yb ion, mainly limited by the quantum efficiency of our photon detector. Besides the high collection efficiency, the integration of an ion trap into a parabolic mirror is a key ingredient for efficient coupling of light to a single ion in free space. © 2012 American Physical Society.

Collectively Enhanced Giant Circular Dichroism of Germanium Nanohelix Square Lattice Arrays - Ellrott, Günter; Beck, Paul; Sultanov, Vitaliy; Rothau, Sergej; Lindlein, Norbert; Chekhova, Maria; Krstic, Vojislav (Advanced Photonics Research, 2023)
Circular dichroism is a unique chiroptical signature of the chirality of a system and is a prevalent way to characterize and distinguish systems on a fundamental level and for their technological applicability. Thus, engineering and maximizing the chiroptical response of a single chiral object or a metasurface composed of chiral entities is a formidable task. Current efforts strongly focus on individual metallic nanostructures and their periodic ensembles to harvest on (resonant) plasmonic properties and interactions. This route, however, waives the advantages of high-refractive-index nanoscale materials embracing low dissipative losses at optical wavelengths and electromagnetic fields penetrating and propagating in such materials. Herein, a strong circular dichroism is demonstrated in square lattices of nanohelices made of the high-refractive-index semiconductor germanium, with dissymmetry factors outperforming metal-based ensembles. The observation of a much higher dissymmetry emerges for illumination with spatially coherent light, in comparison to spatially incoherent light. High dissymmetry is attributed to cooperative coupling between single helices, resulting from the combination of dielectric resonances of both the individual helical building blocks and the highly ordered lattice.<br

Colloquium: The Einstein-Podolsky-Rosen paradox: From concepts to applications - Leuchs, Gerd; et al. (Reviews of Modern Physics, 2009)
This Colloquium examines the field of the Einstein, Podolsky, and Rosen (EPR) gedanken experiment, from the original paper of Einstein, Podolsky, and Rosen, through to modern theoretical proposals of how to realize both the continuous-variable and discrete versions of the EPR paradox. The relationship with entanglement and Bell's theorem are analyzed, and the progress to date towards experimental confirmation of the EPR paradox is summarized, with a detailed treatment of the continuous-variable paradox in laser-based experiments. Practical techniques covered include continuous-wave parametric amplifier and optical fiber quantum soliton experiments. Current proposals for extending EPR experiments to massive-particle systems are discussed, including spin squeezing, atomic position entanglement, and quadrature entanglement in ultracold atoms. Finally, applications of this technology to quantum key distribution, quantum teleportation, and entanglement swapping are examined. © 2009 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.optik.1optik.colloq

Combined diffractive optical elements for quasi-absolute testing of aspherics - Lindlein, Norbert; et al. (Optical Fabrication and Testing, OFT 2006, 2006)
Three position quasi-absolute test for aspherics by using combined-diffractive optical elements is presented. We discuss the effects of substrate quality of DOE on the proposed calibration procedure and present an optimised design of the DOE. © 2006 Optical Society of America.

Combined search for neutrinos from dark matter self-annihilation in the Galactic Center with ANTARES and IceCube - Albert, A.; Andre, M.; Domi, Alba; Anghinolfi, M.; Ardid, M.; Aubert, J-J; Aublin, J.; Baret, B.; Basa, S.; Belhorma, B.; Bertin,; Biagi, Simone; et al. (Physical Review D, 2020)
We present the results of the first combined dark matter search targeting the Galactic Center using the ANTARES and IceCube neutrino telescopes. For dark matter particles with masses from 50 to 1000 GeV, the sensitivities on the self-annihilation cross section set by ANTARES and IceCube are comparable, making this mass range particularly interesting for a joint analysis. Dark matter self-annihilation through the tau(+)tau(-) , mu(+)mu(-) , b (b) over bar, and W+W- channels is considered for both the Navarro-Frenk-White and Burkert halo profiles. In the combination of 2101.6 days of ANTARES data and 1007 days of IceCube data, no excess over the expected background is observed. Limits on the thermally averaged dark matter annihilation cross section are set. These limits present an improvement of up to a factor of 2 in the studied dark matter mass range with respect to the individual limits published by both collaborations. When considering dark matter particles with a mass of 200 GeV annihilating through the tau(+)tau(-)channel, the value obtained for the limit is 7.44 x 10(-24) cm(3) s(-1 )for the Navarro-Frenk-White halo profile. For the purpose of this joint analysis, the model parameters and the likelihood are unified, providing a benchmark for forthcoming dark matter searches performed by neutrino telescopes.
CRIS-Team WoS Importer:2020-11-13

Comparison between an analytical asymptotic fiber drawing model with full Navier-Stokes solution taking into account the effects of inner pressure and surface tension - Luzi, Giovanni; Epple, Philipp; Scharrer, Michael; Fujimoto Meinecke, Ken; Rauh, Cornelia; Delgado, Antonio (Journal of Lightwave Technology, 2011)
A fluid-mechanics model that make use of asymptotic analysis based on small aspect ratio of capillaries has been compared with the full 3-D set of the N.-St. equations, for modelling the fabrication of capillary tubes. The final asymptotic equations are solved numerically and then compared with the N.-St. solutions, obtained with a commercial finite elements solver. The present paper focuses on the comparison of the solution of the two methods taking into account the effects of surface tension and internal hole pressure, since those are of essential importance during drawing. It is shown that the analytical asymptotic method delivers reliable results for practical applications, as long as the inner pressure or the temperature does not exceed too high values. © 2011 IEEE.
UnivIS-Import:2015-03-09:Pub.2011.tech.ITC.stmmec.compar
Keywords: Asymptotic analysis; holey fibres; mathematical modelling; microstructured optical fibres (MOFs); numerical methods; photonic crystal fibres

Comparison of back focal plane imaging of nitrogen vacancy centers in nanodiamond and core-shell CdSe/CdS quantum dots - Christinck, J.; Rodiek, B.; López, M.; Georgieva, H.; Hofer, H.; Götzinger, Stephan; Kück, S. (Journal of Physics: Conference Series, 2022)
We report on the characterization of the angular-dependent emission of two different single-photon emitters based on nitrogen-vacancy centers in nanodiamond and on core-shell CdSe/CdS quantum dot nanoparticles. The emitters were characterized in a confocal microscope setup by spectroscopy and Hanbury-Brown and Twiss interferometry. The angular-dependent emission is measured using a back focal plane imaging technique. A theoretical model of the angular emission patterns of the 2D dipoles of the emitters is developed to determine their orientation. Experiment and model agree well with each other.
CRIS-Team Scopus Importer:2022-02-11

Comparison of parameter-adapted segmentation methods for fluorescence micrographs - Held, Christian; Palmisano, Ralf; Häberle, Lothar; Hensel, Michael; Wittenberg, Thomas (Cytometry Part A, 2011)
Interpreting images from fluorescence microscopy is often a time-consuming task with poor reproducibility. Various image processing routines that can help investigators evaluate the images are therefore useful. The critical aspect for a reliable automatic image analysis system is a robust segmentation algorithm that can perform accurate segmentation for different cell types. In this study, several image segmentation methods were therefore compared and evaluated in order to identify the most appropriate segmentation schemes that are usable with little new parameterization and robustly with different types of fluorescence-stained cells for various biological and biomedical tasks. The study investigated, compared, and enhanced four different methods for segmentation of cultured epithelial cells. The maximum-intensity linking (MIL) method, an improved MIL, a watershed method, and an improved watershed method based on morphological reconstruction were used. Three manually annotated datasets consisting of 261, 817, and 1,333 HeLa or L929 cells were used to compare the different algorithms. The comparisons and evaluations showed that the segmentation performance of methods based on the watershed transform was significantly superior to the performance of the MIL method. The results also indicate that using morphological opening by reconstruction can improve the segmentation of cells stained with a marker that exhibits the dotted surface of cells

Comparison of phase unwrapping algorithms applied to singular phase fields - Seifert, Kristina Johanna; Berger, Andreas; Mantel, Klaus Peter; Nercissian, Vanusch; Lindlein, Norbert (DGaO Proceedings, 2012)

Compensation for Anamorphotic Distortion in Grazing-Incidence Interferometry Testing Planar Specimes - Schneider, Jessica; Mantel, Klaus Peter; Schreiner, Roland; Lindlein, Norbert; Schwider, Johannes (Applied Optics, 2003)
UnivIS-Import:2015-04-14:Pub.2003.nat.dphy.optik.1optik.compen

Compensation of Nonlinear Phase Noise Using the Effective Negative Nonlinearity of a Nonlinear Amplifying Loop Mirror - Sponsel, Klaus; Stephan, Christian; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (IEEE Journal of Selected Topics in Quantum Electronics, 2012)
The nonlinear amplifying loop mirror (NALM) has been explored for use as a nonlinear phase-shift compensator (NPSC). Operation conditions for a tunable effective negative nonlinearity are considered and the NALM parameter optimization is discussed for direct bit-error-ratio (BER) improvement by postcompensation after a nonlinear transmission line. In this configuration, the fundamental limits for NPSC are estimated for differential quadrature phase-shift keying (DQPSK) using a simplified model. Numerical simulations of a 20 Gb/s RZ-DQPSK transmission system confirmed the applicability of this model and showed a significant BER improvement in a realistic transmission line. Alternatively, the fiber launch power per span could be increased by 2 dB for the same BE
lhft_intern.bib::Sponsel2012

Compensation of the wavelength dependence in diffractive star couplers - Lindlein, Norbert; et al. (Journal of the Optical Society of America A-Optics Image Science and Vision, 1995)
A space-variant and a space-invariant approach for decreasing the wavelength dependence of diffractive fan-out systems was presented. Applying diffractive optical elements (DOEs) for the wave-front correction in the space-variant system, the spot sizes were lessened by half the spot sizes over a wavelength range of 20 nm. The paraxial design of the space-invariant system revealed that at least two diffractive lenses were needed. The resulting space-invariant system gave a nearly diffraction-limited performance for a wavelength range from 830 to 850 nm. A summary of the results for all three system designs were also provided.
UnivIS-Import:2015-03-05:Pub.1995.nat.dphy.optik.1optik.compen

Complex source beam: A tool to describe highly focused vector beams analytically - Orlov, S.; Peschel, Ulf (Physical Review A, 2010)
The scalar-complex-source model is used to develop an accurate description of highly focused radially, azimuthally, linearly, and circularly polarized monochromatic vector beams. We investigate the power and full beam widths at half maximum of vigorous Maxwell equation solutions. The analytical expressions are employed to compare the vector complex source beams with the real beams produced by various high-numerical-aperture (NA) focusing systems. We find a parameter set for which the spatial extents of the analytical beams are the same as those of experimentally realized ones. We ensure the same shape of the considered beams by investigating an overlap of the complex source beams with high-NA beams. We demonstrate that the analytical expressions are good approximations for realistic highly focused beams.
EAM Import::2019-03-13

Computer-Aided Design and Simulation of Spatial Opto-Mechatronic Interconnect Devices - Zeitler, Jochen Tobias; Reichle, Andreas; Franke, Jörg; Loosen, Florian; Backhaus, Carsten; Lindlein, Norbert (26th CIRP Design Conference, 2016, 2016)
Optical technologies become increasingly important in modern sensor and communication applications. Nevertheless, manufacturing and design methods in the field of spatial opto-electronics have not been investigated intensively yet. A new approach is to print polymer waveguides on spatial carriers to use the full design freedom of opto-mechatronic assemblies. Up to now, no specific design tools and validation methods are available. The article describes possible technology-specific methods for designing spatial opto-mechatronic applications with the focus on computer-aided design (CAD) and raytracing simulation of spatial waveguides.
Keywords: computer-aided design (CAD); design method; optical communication; opto-electronics; simulation

Computer generiertes Hologramm als punktsymmetrische Streuplatte - Hampp, Heiko; Harder, Irina; Lano, Maik; Lindlein, Norbert (DGaO-Proceedings 2010 - http://www.dgao-proceedings.de - ISSN: 1614-8436, 2010)

Concentration of phase-information - Usuga, Mario; Müller, Christian; Wittmann, Christoffer; Marek, Petr; Filip, Radim; Marquardt, Christoph; Andersen, Ulrik L.A.; Leuchs, Gerd (Optics InfoBase Conference Papers, 2010)
We demonstrate a probabilistic scheme capable of increasing the phase information of weak coherent states by addition of thermal noise and subsequent photon-counting based postselection. We present experimental and theoretical results. © 2010 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

Concentric ring metal grating for generating radially polarized light - Ghadyani, Zahra; Harder, Irina; Lindlein, Norbert; Berger, Andreas; Iff, Wolfgang; Vartiainen, Ismo; Kuittinen, M (Applied Optics, 2011)

Concepts for the design and optimization process of printed polymer-based optical waveguides (scattering processes) - Loosen, Florian; Backhaus, Carsten; Lindlein, Norbert; Zeitler, Jochen Tobias; Franke, Jörg (Proceeding, 4th doctoral students conference on optics (DoKDoK), 2015)

Confocal Microscopy with a Refractive Microlens/Pinhole Array - Lindlein, Norbert; et al. (Optics Letters, 1998)
The stable setup of a confocal arrangement consisting of a combination of a refractive microlens and a pinhole array is presented. The focal plane of the microlenses lies at the rear surface of the substrate in the pinhole plane. By using a microscope objective one can image the stop array onto the object at a reduced size. Surface profiles of refractive and diffractive optical elements were measured with the help of this confocal microscope. © 1998 Optical Society of America.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.confoc

Conical-shaped titania nanotubes for optimized light management in DSSCs reach back-side illumination efficiencies > 8% - So, Seulgi; Kriesch, Arian; Peschel, Ulf; Schmuki, Patrik (Journal of Materials Chemistry A, 2015)
In the present work, we introduce the anodic growth of conical shaped TiO2 nanotube arrays. These titania nanocones provide a scaffold for dye-sensitized solar cell (DSSC) structures with significantly improved photon management, providing an optimized absorption profile compared with conventional cylindrical nanotube arrays. Finite difference time domain (FDTD) modelling demonstrates a drastically changed power-absorption characteristic over the tube length. When used in a back-side illumination DSSC configuration, nanocone structures can reach over 60% higher solar cell conversion efficiency ( extgreekh) than conventional tubes. The resulting extgreekh ≈ 8% represents one of the highest reported values for Grätzel type DSSCs used under back-side illumination.
EAM Import::2019-03-13

Connection of anisotropic conductivity to tip-induced space-charge layers in scanning tunneling spectroscopy of p-doped GaAs - Loth, Sebastian; Wenderoth, Martin; Ulbrich, Rainer G.; Malzer, Stefan; Döhler, Gottfried (Physical Review B, 2007)
The electronic properties of shallow acceptors in p -doped GaAs110 are investigated with scanning tunneling microscopy (STM) at low temperature. Shallow acceptors are known to exhibit distinct triangular contrasts in STM images for certain bias voltages. Spatially resolved I (V) spectroscopy is performed to identify their energetic origin and behavior. A crucial parameter-the scanning tunneling microscope tip's work function-is determined experimentally. The voltage dependent potential configuration and band bending situation are derived. Ways to validate the calculations with the experiment are discussed. Differential conductivity maps reveal that the triangular contrasts are only observed with a depletion layer present under the STM tip. The tunnel process leading to the anisotropic contrasts calls for electrons to tunnel through vacuum gap and a finite region in the semiconductor. © 2007 The American Physical Society.

Consequences of EEG electrode position error on ultimate beamformer source reconstruction performance - Dalal, Sarang S.; Rampp, Stefan; Willomitzer, Florian; Ettl, Svenja (Frontiers in Neuroscience, 2014)
Inaccuracy of EEG electrode coordinates forms an error term in forward model generation and ultimate source reconstruction performance. This error arises from the combination of both intrinsic measurement noise of the digitization apparatus and manual coregistration error when selecting corresponding points on anatomical MRI volumes. A common assumption is that such an error would lead only to displacement of localized sources. Here, we measured electrode positions on a 3D-printed full-scale replica head, using three different techniques: a fringe projection 3D scanner, a novel "Flying Triangulation" 3D sensor, and a traditional electromagnetic digitizer. Using highly accurate fringe projection data as ground truth, the Flying Triangulation sensor had a mean error of 1.5 mm while the electromagnetic digitizer had a mean error of 6.8 mm. Then, again using the fringe projection as ground truth, individual EEG simulations were generated, with source locations across the brain space and a range of sensor noise levels. The simulated datasets were then processed using a beamformer in conjunction with the electrode coordinates registered with the Flying Triangulation and electromagnetic digitizer methods. The beamformer's output SNR was severely degraded with the digitizer-based positions but less severely with the Flying Triangulation coordinates. Therefore, the seemingly innocuous error in electrode registration may result in substantial degradation of beamformer performance, with output SNR penalties up to several decibels. In the case of low-SNR signals such as deeper brain structures or gamma band sources, this implies that sensor coregistration accuracy could make the difference between successful detection of such activity or complete failure to resolve the source.
EVALuna2:22315

Continuos Wave Terahertz Emitter Arrays for Spectroscopy and Imaging Applications - Bauerschmidt, Sebastian; Malzer, Stefan; Preu, Sascha; Döhler, Gottfried; Lu, Hong; Gossard, Art; Wang, Lijun (Proceedings of SPIE, 2010)
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.LAP.contin

Continuous counting, sizing and refractive index measurement of airborne particles in hollow-core photonic crystal fibre - Sharma, Abhinav; Xie, Shangran; Zeltner, Richard; Russell, Philip St. John (Proceedings of SPIE - The International Society for Optical Engineering, 2019)
Air pollution by particles of aerodynamic diameter less than 2.5 μm (PM2.5) is currently an important environmental issue. As standard methods for monitoring and characterization are time-consuming and expensive, there is need for a simple, effective and inexpensive device for real-Time PM2.5 monitoring. Although optical methods based on the scattering of laser beams exist, they do not provide independent measurement of particle size and refractive index. In systems based on detection in an evanescent optical field, particles tend to adhere to the surface, strongly limiting the device lifetime. Here we report a new approach to airborne particle characterization that makes use of hollow-core photonic crystal fibre (HC-PCF). Employing optical gradient and radiation forces to trap and propel airborne particles along the hollow core, it provides in situ particle counting, sizing and refractive index measurement in real-Time with effectively unlimited device lifetime. We show that the transmission drop and time-of-flight can be unambiguously mapped to particle size and refractive index.
CRIS-Team Scopus Importer:2019-10-22
Keywords: Optical trapping and manipulation; Photonic crystal fibre; PM

Continuously adjustable narrow-band heralded single photon source - Förtsch, Michael; Fürst, Josef; Wittmann, Christoffer; Strekalov, Dmitry; Aiello, Andrea; Silberhorn, Christine; Marquardt, Christoph; Leuchs, Gerd (2012 Conference on Lasers and Electro-Optics, CLEO 2012, 2012)
We present the high efficient generation of narrow-band heralded single photons, widely tunable in wavelength and bandwidth using resonator enhanced spontaneous down conversion in a crystalline whispering gallery mode resonator. © 2012 OSA.
CRIS-Team Scopus Importer:2022-06-05

Continuous Variable Entanglement and Squeezing of Orbital Angular Momentum States - Lassen, Mikael Ostergaard; Leuchs, Gerd; Andersen, Ulrik Lund (Physical Review Letters, 2009)
We report the first experimental characterization of the first-order continuous variable orbital angular momentum states. Using a spatially nondegenerate optical parametric oscillator (OPO) we produce quadrature entanglement between the two first-order Laguerre-Gauss modes. The family of orbital angular momentum modes is mapped on an orbital Poincaré sphere, where the mode's position on the sphere is spanned by the three orbital parameters. Using a nondegenerate OPO we produce squeezing of these parameters, and as an illustration, we reconstruct the "cigar-shaped" uncertainty volume on the orbital Poincaré sphere. © 2009 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.optik.1optik.contin

Continuous variable entanglement between frequency modes - Leuchs, Gerd; et al. (Fortschritte Der Physik-Progress of Physics, 2006)
The pairwise production of photons in nonlinear optical processes ensures entanglement to occur between two photons. E.g. when the Kerr effect is exploited, the photons are produced in different frequency modes, which are symmetric with respect to the pump frequency. Since these photons are produced into the same spatial mode, the quadrature entanglement can be witnessed only by the use of a frequency selective device which transforms the adjacent frequency modes into two different spatial modes. We use a Mach-Zehnder interferometer with a large path length difference to separate symmetric frequency modes located 10.25 MHz from the carrier. We measure correlations of the quadrature components of 1.6 ± 0.1dB below the shot noise in the amplitude and 1.4 ± 0.1dB in the phase. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.contin

Continuous-variable entanglement distillation of non-Gaussian mixed states - Dong, Ruifang; Lassen, Mikael; Heersink, Joel; Marquardt, Christoph; Filip, Radim; Leuchs, Gerd; Andersen, Ulrik L. (Physical Review A - Atomic, Molecular, and Optical Physics, 2010)
Many different quantum-information communication protocols such as teleportation, dense coding, and entanglement-based quantum key distribution are based on the faithful transmission of entanglement between distant location in an optical network. The distribution of entanglement in such a network is, however, hampered by loss and noise that is inherent in all practical quantum channels. Thus, to enable faithful transmission one must resort to the protocol of entanglement distillation. In this paper we present a detailed theoretical analysis and an experimental realization of continuous variable entanglement distillation in a channel that is inflicted by different kinds of non-Gaussian noise. The continuous variable entangled states are generated by exploiting the third order nonlinearity in optical fibers, and the states are sent through a free-space laboratory channel in which the losses are altered to simulate a free-space atmospheric channel with varying losses. We use linear optical components, homodyne measurements, and classical communication to distill the entanglement, and we find that by using this method the entanglement can be probabilistically increased for some specific non-Gaussian noise channels. © 2010 The American Physical Society.
CRIS-Team Scopus Importer:2022-06-05

Continuous variable entanglement distillation of non-gaussian states - Lassen, Mikael Ostergaard; Dong, Ruifang; Heersink, Joel; Marquardt, Christoph; Filip, Radim; Leuchs, Gerd; Ulrik, L. Andersen (AIP Conference Proceedings, 2009)
We experimentally demonstrate distillation of continuous variable entangled light that has undergone non-Gaussian attenuation loss. The continuous variable entanglement is generated with optical fibers and sent through a lossy channel, where the transmission is varying in time. By employing simple linear optical components, a measurement induced operation and classical communication, we demonstrate that the entanglement is probabilistically increased. © 2009 American Institute of Physics.
CRIS-Team Scopus Importer:2022-06-05
Keywords: Distillation; Entanglement; Quantum information

Continuous variable free space quantum communication - Leuchs, Gerd; Marquardt, Christoph (Optics InfoBase Conference Papers, 2016)
Continuous variable free space quantum communication offers high-speed distribution of quantum states for quantum key distribution under daylight condition. We report our activities on experimental investigations ranging from intra-city links to satellite based communication.
CRIS-Team Scopus Importer:2022-06-05

Continuous variable quantum communication - Andersen, Ulrik Lund; Leuchs, Gerd (Lectures on Quantum Information, 2006)
UnivIS-Import:2015-04-20:Pub.2006.nat.dphy.optik.1optik.contin_6

Continuous Variable Quantum Communication with Gaussian States - Andersen, Ulrik Lund; Leuchs, Gerd (Quantum Information: From Foundations to Quantum Technology Applications, 2019)
CRIS-Team WoS Importer:2020-09-25

Continuous Variable Quantum Cryptography - beating the 3dB loss limit - Leuchs, Gerd; et al. (Physical Review Letters, 2002)
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.optik.1optik.contin

Continuous variable quantum key distribution using polarization encoding and post selection - Leuchs, Gerd; et al. (Applied Physics B-Lasers and Optics, 2004)
We present an experimental demonstration of a quantum key distribution protocol using coherent polarization states. Post selection is used to ensure a low error rate and security against beam-splitting attacks even in the presence of high losses. Signal encoding and readout in polarization bases avoids the difficult task of sending a local oscillator with the quantum channel. This makes our setup robust and easy to implement. A shared key was established for losses up to 64%.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.optik.1optik.contin

Continuous-Wave Sub-THz Photonic Generation With Ultra-Narrow Linewidth, Ultra-High Resolution, Full Frequency Range Coverage and High Long-Term Frequency Stability - Malzer, Stefan; Criado, Ruben; de Dios, Christina; Preu, Sascha; Prior, E.; Acedo, Pablo; Döhler, Gottfried; Lu, Hong; Gossard, Art (IEEE Transactions on Terahertz Science and Technology, 2013)
We report on a photonic system for generation of high quality continuous-wave (CW) sub-THz signals. The system consists on a gain-switching-based optical frequency comb generator (GS-OFCG), a two-optical-modes selection mechanism and a n-i-pn-i-p superlattice photomixer. As mode selection mechanism, both selective tunable optical filtering using Fabry-Pérot tunable filters (FPTFs) and Optical Injection Locking (OIL) are evaluated. The performance of the reported system surpasses in orders of magnitude the performance of any commercially available optical mm-wave and sub-THz generation system in a great number of parameters. It matches and even overcomes those of the best commercially available electronic THz generation systems. The performance parameters featured by our system are: linewidth 10 Hz at 120 GHz, complete frequency range coverage (60-140 GHz) with a resolution in the order of 0.1 Hz at 120 GHz ( 10 of generated frequency), high long term frequency stability (5 Hz deviation over one hour). Most of these values are limited by the measurement instrumentation accuracy and resolution, thus the actual values of the system could be better than the reported ones. The frequency can be extended straightforwardly up to 1 THz extending the OFCG frequency span. This system is compact, robust, reliable, offers a very high performance, especially suited for sub-THz photonic local oscillators and high resolution spectroscopy.

Continuous wave terahertz emitter arrays for spectroscopy and imaging applications - Bauerschmidt, Sebastian; Preu, Sascha; Malzer, Stefan; Döhler, Gottfried; Wang, Lijun; Lu, Hong; Gossard, Art (Terahertz Physics, Devices, and Systems IV: Advanced Applications in Industry and Defense, 2010)
We report on arrays of THz-emitters based on n-i-pn-i-p-superlattice photomixers for imaging and spectroscopic applications. The output power of a n-i-pn-i-p superlattice photomixers recently has reached nearly 1 μW at 1 THz with a broadband antenna. There are no fundamental physical limitations at this stage for further improvement. Tunable continuous wave (CW) THz-sources for imaging and spectroscopy are highly desired tools for security and environmental applications. In particular, most stand-off imaging applications require a rather high THz power to allow for a sufficient dynamic range, and a narrow illumination spot size for high spatial resolution. Both goals can be reached by using an array of mutually coherent photomixers. We have simulated beam patterns for an arbitrary number of mutually coherent single sources with respect to a small beam size and high peak intensity. Here, we confirm the simulations experimentally by an array of 4 sources with a 4 inch THz optics. The beam profile is measured in the target plane at a stand-off distance of 4.2 m. As a result, the beam diameter is reduced by a factor of 6 and the peak intensity is enhanced by a factor of close to (4) = 16, in excellent agreement with our simulations. Such an arrangement allows not only for high resolution stand-off imaging but also for spectroscopic investigations at stand-off distances. The THz frequency can be tuned over more than a decade (i.e. 0.1 to 2.5 THz) by tuning the wavelength of the mixing lasers. The spectral linewidth of the THz sources is only limited by the linewidths of the mixing lasers and can be made extremely narrow. A straightforward demonstration is achieved by water vapor spectroscopy in laboratory air with a single source. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Controlled generation of intrinsic near-infrared color centers in 4H-SiC via proton irradiation and annealing - Rühl, Maximilian; Ott, Christian; Götzinger, Stephan; Krieger, Michael; Weber, Heiko B. (Applied Physics Letters, 2018)
We report on the generation and annihilation of color centers in 4H silicon carbide (SiC) by proton irradiation and subsequent annealing. Using low-temperature photoluminescence (PL), we study the transformation of PL spectra for different proton doses and annealing temperatures. Among well reported defect signatures, we observe omnipresent but not yet identified PL signatures consisting of three sharp and temperature stable lines (denoted TS1,2,3) at 768.8 nm, 812.0 nm, and 813.3 nm. These lines show a strong correlation throughout all measurement parameters, suggesting that they belong to the same microscopic defect. Further, a clear dependence of the TS1,2,3 line intensities on the initial implantation dose is observed after annealing, indicating that the underlying defect is related to implantation induced intrinsic defects. The overall data suggest a sequential defect transformation: proton irradiation initially generates isolated silicon vacancies which are transformed into antisite vacancy complexes which are, in turn, transformed into presumably intrinsic-related defects, showing up as TS1,2,3 PL lines. We present recipes for the controlled generation of these color center
Keywords: Farbzentren

Controlled Synthesis and Dissociation of Soliton Molecules Using Parallel Reactors in Optomechanical Lattice - He, Wenbin; Pang, Meng; Yeh, Dung-Han; Russell, Philip St. John (2020 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR), 2020)
CRIS-Team WoS Importer:2021-06-11