@article{44088,
  abstract     = {{Hole polarons and defect-bound exciton polarons in lithium niobate are investigated by means of density-functional theory, where the localization of the holes is achieved by applying the +U approach to the oxygen 2p orbitals. We find three principal configurations of hole polarons: (i) self-trapped holes localized at displaced regular oxygen atoms and (ii) two other configurations bound to a lithium vacancy either at a threefold coordinated oxygen atom above or at a two-fold coordinated oxygen atom below the defect. The latter is the most stable and is in excellent quantitative agreement with measured g factors from electron paramagnetic resonance. Due to the absence of mid-gap states, none of these hole polarons can explain the broad optical absorption centered between 2.5 and 2.8 eV that is observed in transient absorption spectroscopy, but such states appear if a free electron polaron is trapped at the same lithium vacancy as the bound hole polaron, resulting in an exciton polaron. The dielectric function calculated by solving the Bethe–Salpeter equation indeed yields an optical peak at 2.6 eV in agreement with the two-photon experiments. The coexistence of hole and exciton polarons, which are simultaneously created in optical excitations, thus satisfactorily explains the reported experimental data.}},
  author       = {{Schmidt, Falko and Kozub, Agnieszka L. and Gerstmann, Uwe and Schmidt, Wolf Gero and Schindlmayr, Arno}},
  issn         = {{2073-4352}},
  journal      = {{Crystals}},
  number       = {{11}},
  publisher    = {{MDPI AG}},
  title        = {{{A density-functional theory study of hole and defect-bound exciton polarons in lithium niobate}}},
  doi          = {{10.3390/cryst12111586}},
  volume       = {{12}},
  year         = {{2022}},
}

@article{34230,
  abstract     = {{We present the design and experimental characterization of a silicon nitride pulse interleaver based on coupled resonator optical waveguide filters. In order to achieve a targeted free spectral range of 1.44 THz, which is large given the reduced optical confinement of the silicon nitride platform, individual ring resonators are designed with tapered waveguides. Its application to time-interleaved photonically-assisted ADCs is analyzed by combining experimental characterization of the photonic integrated circuit with a comprehensive model of the entire ADC. The impact of fundamental signal distortion and noise sources affecting the converter is investigated and suitable equalization techniques at the digital signal processing level are evaluated. The novel application of a simple but powerful equalization filter in the DSP domain allows for a significant improvement of the digitized signal SNR. An ENOB of 5 over a 75 GHz bandwidth (150 GS/s) and an ENOB of 4.3 over a 100 GHz bandwidth (200 GS/s) are expected to be achievable with compact and off-the-shelf single-section semiconductor mode locked lasers, that can be further improved with lower noise light sources.}},
  author       = {{Zazzi, Andrea and Müller, Juliana and Ghannam, Ibrahim and Battermann, Moritz and Rajeswari, Gayatri Vasudevan and Weizel, Maxim and Scheytt, J. Christoph and Witzens, Jeremy}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{3}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Wideband SiN pulse interleaver for optically-enabled analog-to-digital conversion: a device-to-system analysis with cyclic equalization}}},
  doi          = {{10.1364/oe.441406}},
  volume       = {{30}},
  year         = {{2022}},
}

@article{34239,
  author       = {{Bahmanian, Meysam and Scheytt, J. Christoph}},
  issn         = {{0018-9480}},
  journal      = {{IEEE Transactions on Microwave Theory and Techniques}},
  number       = {{10}},
  pages        = {{4422--4435}},
  publisher    = {{Institute of Electrical and Electronics Engineers (IEEE)}},
  title        = {{{Noise Processes and Nonlinear Mechanisms in Optoelectronic Phase-Locked Loop Using a Balanced Optical Microwave Phase Detector}}},
  doi          = {{10.1109/tmtt.2022.3197621}},
  volume       = {{70}},
  year         = {{2022}},
}

@article{34094,
  author       = {{Gao, Ying and Li, Yao and Ma, Xuekai and Gao, Meini and Dai, Haitao and Schumacher, Stefan and Gao, Tingge}},
  issn         = {{0003-6951}},
  journal      = {{Applied Physics Letters}},
  keywords     = {{Physics and Astronomy (miscellaneous)}},
  number       = {{20}},
  publisher    = {{AIP Publishing}},
  title        = {{{Tilting nondispersive bands in an empty microcavity}}},
  doi          = {{10.1063/5.0093908}},
  volume       = {{121}},
  year         = {{2022}},
}

@article{31937,
  author       = {{Li, Yao and Ma, Xuekai and Hatzopoulos, Zaharias and Savvidis, Pavlos G. and Schumacher, Stefan and Gao, Tingge}},
  issn         = {{2330-4022}},
  journal      = {{ACS Photonics}},
  number       = {{6}},
  pages        = {{2079--2086}},
  publisher    = {{American Chemical Society (ACS)}},
  title        = {{{Switching Off a Microcavity Polariton Condensate near the Exceptional Point}}},
  doi          = {{10.1021/acsphotonics.2c00288}},
  volume       = {{9}},
  year         = {{2022}},
}

@article{37713,
  author       = {{Murzakhanov, Fadis F. and Mamin, Georgy Vladimirovich and Orlinskii, Sergei Borisovich and Gerstmann, Uwe and Schmidt, Wolf Gero and Biktagirov, Timur and Aharonovich, Igor and Gottscholl, Andreas and Sperlich, Andreas and Dyakonov, Vladimir and Soltamov, Victor A.}},
  issn         = {{1530-6984}},
  journal      = {{Nano Letters}},
  keywords     = {{Mechanical Engineering, Condensed Matter Physics, General Materials Science, General Chemistry, Bioengineering}},
  number       = {{7}},
  pages        = {{2718--2724}},
  publisher    = {{American Chemical Society (ACS)}},
  title        = {{{Electron–Nuclear Coherent Coupling and Nuclear Spin Readout through Optically Polarized V<sub>B</sub><sup>–</sup> Spin States in hBN}}},
  doi          = {{10.1021/acs.nanolett.1c04610}},
  volume       = {{22}},
  year         = {{2022}},
}

@article{33080,
  author       = {{Long, Teng and Ma, Xuekai and Ren, Jiahuan and Li, Feng and Liao, Qing and Schumacher, Stefan and Malpuech, Guillaume and Solnyshkov, Dmitry and Fu, Hongbing}},
  issn         = {{2198-3844}},
  journal      = {{Advanced Science}},
  keywords     = {{General Physics and Astronomy, General Engineering, Biochemistry, Genetics and Molecular Biology (miscellaneous), General Materials Science, General Chemical Engineering, Medicine (miscellaneous)}},
  number       = {{29}},
  publisher    = {{Wiley}},
  title        = {{{Helical Polariton Lasing from Topological Valleys in an Organic Crystalline Microcavity}}},
  doi          = {{10.1002/advs.202203588}},
  volume       = {{9}},
  year         = {{2022}},
}

@article{32310,
  author       = {{Li, Yao and Ma, Xuekai and Zhai, Xiaokun and Gao, Meini and Dai, Haitao and Schumacher, Stefan and Gao, Tingge}},
  issn         = {{2041-1723}},
  journal      = {{Nature Communications}},
  keywords     = {{General Physics and Astronomy, General Biochemistry, Genetics and Molecular Biology, General Chemistry, Multidisciplinary}},
  number       = {{1}},
  publisher    = {{Springer Science and Business Media LLC}},
  title        = {{{Manipulating polariton condensates by Rashba-Dresselhaus coupling at room temperature}}},
  doi          = {{10.1038/s41467-022-31529-4}},
  volume       = {{13}},
  year         = {{2022}},
}

@article{32148,
  author       = {{Gao, Xinghui and Hu, Wei and Schumacher, Stefan and Ma, Xuekai}},
  issn         = {{0146-9592}},
  journal      = {{Optics Letters}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{13}},
  pages        = {{3235--3238}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Unidirectional vortex waveguides and multistable vortex pairs in polariton condensates}}},
  doi          = {{10.1364/ol.457724}},
  volume       = {{47}},
  year         = {{2022}},
}

@inbook{30288,
  abstract     = {{Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe-Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.}},
  author       = {{Schmidt, Falko and Kozub, Agnieszka L. and Gerstmann, Uwe and Schmidt, Wolf Gero and Schindlmayr, Arno}},
  booktitle    = {{New Trends in Lithium Niobate: From Bulk to Nanocrystals}},
  editor       = {{Corradi, Gábor and Kovács, László}},
  isbn         = {{978-3-0365-3340-7}},
  pages        = {{231--248}},
  publisher    = {{MDPI}},
  title        = {{{Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response}}},
  doi          = {{10.3390/books978-3-0365-3339-1}},
  year         = {{2022}},
}

@article{40371,
  abstract     = {{<jats:p>Multimode integrated interferometers have great potential for both spectral engineering and metrological applications. However, the material dispersion of integrated platforms constitutes an obstacle that limits the performance and precision of such interferometers. At the same time, two-colour nonlinear interferometers present an important tool for metrological applications, when measurements in a certain frequency range are difficult. In this manuscript, we theoretically developed and investigated an integrated multimode two-colour SU(1,1) interferometer operating in a supersensitive mode. By ensuring the proper design of the integrated platform, we suppressed the dispersion, thereby significantly increasing the visibility of the interference pattern. The use of a continuous wave pump laser provided the symmetry between the spectral shapes of the signal and idler photons concerning half the pump frequency, despite different photon colours. We demonstrate that such an interferometer overcomes the classical phase sensitivity limit for wide parametric gain ranges, when up to 3×104 photons are generated.</jats:p>}},
  author       = {{Ferreri, Alessandro and Sharapova, Polina R.}},
  issn         = {{2073-8994}},
  journal      = {{Symmetry}},
  keywords     = {{Physics and Astronomy (miscellaneous), General Mathematics, Chemistry (miscellaneous), Computer Science (miscellaneous)}},
  number       = {{3}},
  publisher    = {{MDPI AG}},
  title        = {{{Two-Colour Spectrally Multimode Integrated SU(1,1) Interferometer}}},
  doi          = {{10.3390/sym14030552}},
  volume       = {{14}},
  year         = {{2022}},
}

@article{30210,
  abstract     = {{Lithium niobate on insulator (LNOI) has a great potential for photonic integrated circuits, providing substantial versatility in design of various integrated components. To properly use these components in the implementation of different quantum protocols, photons with different properties are required. In this paper, we theoretically demonstrate a flexible source of correlated photons built on the LNOI waveguide of a special geometry. This source is based on the parametric down-conversion (PDC) process, in which the signal and idler photons are generated at the telecom wavelength and have different spatial profiles and polarizations, but the same group velocities. Distinguishability in polarizations and spatial profiles facilitates the routing and manipulating individual photons, while the equality of their group velocities leads to the absence of temporal walk-off between photons. We show how the spectral properties of the generated photons and the number of their frequency modes can be controlled depending on the pump characteristics and the waveguide length. Finally, we discuss special regimes, in which narrowband light with strong frequency correlations and polarization-entangled Bell states are generated at the telecom wavelength.}},
  author       = {{Ebers, Lena and Ferreri, Alessandro and Hammer, Manfred and Albert, Maximilian and Meier, Cedrik and Förstner, Jens and Sharapova, Polina R.}},
  issn         = {{2515-7647}},
  journal      = {{Journal of Physics: Photonics}},
  keywords     = {{tet_topic_waveguide}},
  pages        = {{025001}},
  publisher    = {{IOP Publishing}},
  title        = {{{Flexible source of correlated photons based on LNOI rib waveguides}}},
  doi          = {{10.1088/2515-7647/ac5a5b}},
  volume       = {{4}},
  year         = {{2022}},
}

@article{33670,
  author       = {{Schapeler, Timon and Bartley, Tim}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{1}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Information extraction in photon-counting experiments}}},
  doi          = {{10.1103/physreva.106.013701}},
  volume       = {{106}},
  year         = {{2022}},
}

@inproceedings{63039,
  abstract     = {{<jats:p>We report on coherent transmission of beyond 100 GBd signaling based on plasmonic technology. Using dual-drive plasmonic-organic-hybrid I/Q modulator on silicon photonics platform, we demonstrate the successful transmission of 160-GBaud QPSK and 140-GBaud 16QAM modulations.</jats:p>}},
  author       = {{Mardoyan, Haïk and Jorge, Filipe and Destraz, Marcel and Duval, Bernadette and Bitachon, Bertold and Horst, Yannik and Benyahya, Kaoutar and Blache, Fabrice and Goix, Michel and De Leo, Eva and Habegger, Patrick and Meier, Norbert and Del Medico, Nino and Tedaldi, Valentino and Funck, Christian and Güsken, Nicholas Alexander and Leuthold, Juerg and Renaudier, Jéremie and Hoessbacher, Claudia and Heni, Wolfgang and Baeuerle, Benedikt}},
  booktitle    = {{Optical Fiber Communication Conference (OFC) 2022}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Generation and transmission of 160-Gbaud QPSK Coherent Signals using a Dual-Drive Plasmonic-Organic Hybrid I/Q modulator on Silicon Photonics}}},
  doi          = {{10.1364/ofc.2022.th1j.5}},
  year         = {{2022}},
}

@inproceedings{63041,
  author       = {{Güsken, Nicholas Alexander}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Plasmonic PICs—Terabit Modulation on the Micrometer Scale}}},
  doi          = {{https://opg.optica.org/abstract.cfm?URI=ECEOC-2022-Tu4E.3}},
  year         = {{2022}},
}

@article{30921,
  abstract     = {{Quantum walks function as essential means to implement quantum simulators, allowing one to study complex and often directly inaccessible quantum processes in controllable systems. In this contribution, the notion of a driven Gaussian quantum walk is introduced. In contrast to typically considered quantum walks in optical settings, we describe the operation of the walk in terms of a nonlinear map rather than a unitary operation, e.g., by replacing a beam-splitter-type coin with a two-mode squeezer, being a process that is controlled and driven by a pump field. This opens previously unattainable possibilities for quantum walks that include nonlinear elements as core components of their operation, vastly extending their range of applications. A full framework for driven Gaussian quantum walks is developed, including methods to dynamically characterize nonlinear, quantum, and quantum-nonlinear effects. Moreover, driven Gaussian quantum walks are compared with their classically interfering and linear counterparts, which are based on classical coherence of light rather than quantum superpositions. In particular, the generation and boost of highly multimode entanglement, squeezing, and other quantum effects are studied over the duration of the nonlinear walk. Importantly, we prove the quantumness of the evolution itself, regardless of the input state. A scheme for an experimental realization is proposed. Furthermore, nonlinear properties of driven Gaussian quantum walks are explored, such as amplification that leads to an ever increasing number of correlated quantum particles, constituting a source of new walkers during the walk. Therefore, a concept for quantum walks is proposed that leads to—and even produces—directly accessible quantum phenomena, and that renders the quantum simulation of nonlinear processes possible.}},
  author       = {{Held, Philip and Engelkemeier, Melanie and De, Syamsundar and Barkhofen, Sonja and Sperling, Jan and Silberhorn, Christine}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{4}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Driven Gaussian quantum walks}}},
  doi          = {{10.1103/physreva.105.042210}},
  volume       = {{105}},
  year         = {{2022}},
}

@article{25605,
  abstract     = {{The nonlinear process of second harmonic generation (SHG) in monolayer (1L) transition metal dichalcogenides (TMD), like WS2, strongly depends on the polarization state of the excitation light. By combination of plasmonic nanostructures with 1L-WS2 by transferring it onto a plasmonic nanoantenna array, a hybrid metasurface is realized impacting the polarization dependency of its SHG. Here, we investigate how plasmonic dipole resonances affect the process of SHG in plasmonic–TMD hybrid metasurfaces by nonlinear spectroscopy. We show that the polarization dependency is affected by the lattice structure of plasmonic nanoantenna arrays as well as by the relative orientation between the 1L-WS2 and the individual plasmonic nanoantennas. In addition, such hybrid metasurfaces show SHG in polarization states, where SHG is usually forbidden for either 1L-WS2 or plasmonic nanoantennas. By comparing the SHG in these channels with the SHG generated by the hybrid metasurface components, we detect an enhancement of the SHG signal by a factor of more than 40. Meanwhile, an attenuation of the SHG signal in usually allowed polarization states is observed. Our study provides valuable insight into hybrid systems where symmetries strongly affect the SHG and enable tailored SHG in 1L-WS2 for future applications.}},
  author       = {{Spreyer, Florian and Ruppert, Claudia and Georgi, Philip and Zentgraf, Thomas}},
  issn         = {{1936-0851}},
  journal      = {{ACS Nano}},
  number       = {{10}},
  pages        = {{16719--16728}},
  title        = {{{Influence of Plasmon Resonances and Symmetry Effects on Second Harmonic Generation in WS2–Plasmonic Hybrid Metasurfaces}}},
  doi          = {{10.1021/acsnano.1c06693}},
  volume       = {{15}},
  year         = {{2021}},
}

@article{21631,
  abstract     = {{<jats:p>Secret sharing is a well-established cryptographic primitive for storing highly sensitive information like encryption keys for encoded data. It describes the problem of splitting a secret into different shares, without revealing any information to its shareholders. Here, we demonstrate an all-optical solution for secret sharing based on metasurface holography. In our concept, metasurface holograms are used as spatially separable shares that carry encrypted messages in the form of holographic images. Two of these shares can be recombined by bringing them close together. Light passing through this stack of metasurfaces accumulates the phase shift of both holograms and optically reconstructs the secret with high fidelity. In addition, the hologram generated by each single metasurface can uniquely identify its shareholder. Furthermore, we demonstrate that the inherent translational alignment sensitivity between two stacked metasurface holograms can be used for spatial multiplexing, which can be further extended to realize optical rulers.</jats:p>}},
  author       = {{Georgi, Philip and Wei, Qunshuo and Sain, Basudeb and Schlickriede, Christian and Wang, Yongtian and Huang, Lingling and Zentgraf, Thomas}},
  issn         = {{2375-2548}},
  journal      = {{Science Advances}},
  number       = {{16}},
  title        = {{{Optical secret sharing with cascaded metasurface holography}}},
  doi          = {{10.1126/sciadv.abf9718}},
  volume       = {{7}},
  year         = {{2021}},
}

@article{23842,
  author       = {{Baron, Elias and Feneberg, Martin and Goldhahn, Rüdiger and Deppe, Michael and Tacken, Fabian and As, Donat Josef}},
  issn         = {{0022-3727}},
  journal      = {{Journal of Physics D: Applied Physics}},
  title        = {{{Optical evidence of many-body effects in the zincblende Al$_\mathrm{x}$Ga$_\mathrm{1-x}$N alloy system}}},
  doi          = {{10.1088/1361-6463/abb97a}},
  year         = {{2021}},
}

@article{20592,
  abstract     = {{GaAs-(111)-nanostructures exhibiting second harmonic generation are new building blocks in nonlinear optics. Such structures can be fabricated through epitaxial lift-off using selective etching of Al-containing layers and subsequent transfer to glass substrates. Herein, the selective etching of (111)B-oriented AlxGa1−xAs sacrificial layers (10–50 nm thick) with different aluminum concentrations (x = 0.5–1.0) in 10\% hydrofluoric acid is investigated and compared with standard (100)-oriented structures. The thinner the sacrificial layer and the lower the aluminum content, the lower the lateral etch rate. For both orientations, the lateral etch rates are in the same order of magnitude, but some quantitative differences exist. Furthermore, the epitaxial lift-off, the transfer, and the nanopatterning of thin (111)B-oriented GaAs membranes are demonstrated. Atomic force microscopy and high-resolution X-ray diffraction measurements reveal the high structural quality of the transferred GaAs-(111) films.}},
  author       = {{Henksmeier, Tobias and Eppinger, Martin and Reineke, Bernhard and Zentgraf, Thomas and Meier, Cedrik and Reuter, Dirk}},
  journal      = {{physica status solidi (a)}},
  keywords     = {{epitaxial lift-off, GaAs/AlxGa1−xAs heterostructures, selective etching}},
  number       = {{3}},
  pages        = {{2000408}},
  title        = {{{Selective Etching of (111)B-Oriented AlxGa1−xAs-Layers for Epitaxial Lift-Off}}},
  doi          = {{https://doi.org/10.1002/pssa.202000408}},
  volume       = {{218}},
  year         = {{2021}},
}