@article{31329,
  abstract     = {{Highly directive antennas with the ability of shaping radiation patterns in desired directions are essential for efficient on-chip optical communication with reduced cross talk. In this paper, we design and optimize three distinct broadband traveling-wave tantalum pentoxide antennas exhibiting highly directional characteristics. Our antennas contain a director and reflector deposited on a glass substrate, which are excited by a dipole emitter placed in the feed gap between the two elements. Full-wave simulations in conjunction with global optimization provide structures with an enhanced linear directivity as high as 119 radiating in the substrate. The high directivity is a result of the interplay between two dominant TE modes and the leaky modes present in the antenna director. Furthermore, these low-loss dielectric antennas exhibit a near-unity radiation efficiency at the operational wavelength of 780 nm and maintain a broad bandwidth. Our numerical results are in good agreement with experimental measurements from the optimized antennas fabricated using a two-step electron-beam lithography, revealing the highly directive nature of our structures. We envision that our antenna designs can be conveniently adapted to other dielectric materials and prove instrumental for inter-chip optical communications and other on-chip applications.}},
  author       = {{Farheen, Henna and Yan, Lok-Yee and Quiring, Viktor and Eigner, Christof and Zentgraf, Thomas and Linden, Stefan and Förstner, Jens and Myroshnychenko, Viktor}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{tet_topic_opticalantenna}},
  number       = {{11}},
  pages        = {{19288}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Broadband optical Ta2O5 antennas for directional emission of light}}},
  doi          = {{10.1364/oe.455815}},
  volume       = {{30}},
  year         = {{2022}},
}

@article{34232,
  abstract     = {{<jats:p>In this paper, the theory of phase-locking of a microwave oscillator on the interharmonics, i.e. non-integer harmonics, of the repetition rate of the optical pulse train of a mode-locked laser (MLL) is developed. A balanced optical microwave phase detector (BOMPD) is implemented using a balanced Mach-Zehnder modulator and is employed to discriminate the phase difference between the envelope of the optical pulses and the microwave oscillator. It is shown mathematically that the inherent nonlinear properties of BOMPD with respect to the microwave excitation amplitude can be used for interharmonic locking. The characteristic functions of the phase detector for interharmonic locking are derived analytically and are compared with the measurement results. An opto-electronic phase-locked loop (OEPLL) is demonstrated whose output frequency locks on interharmonics of the MLL repetition rate when an appropriate modulator bias and sufficient RF amplitude are applied. Thus, for the first time theory and experiment of reliable locking on interharmonics of the repetition rate of a MLL are presented.</jats:p>}},
  author       = {{Bahmanian, Meysam and Kress, Christian and Scheytt, J. Christoph}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{5}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Locking of microwave oscillators on the interharmonics of mode-locked laser signals}}},
  doi          = {{10.1364/oe.451894}},
  volume       = {{30}},
  year         = {{2022}},
}

@article{34235,
  abstract     = {{<jats:p>We demonstrate for the first time, to the best of our knowledge, reconfigurable and real-time orthogonal time-domain detection of a high-bandwidth Nyquist signal with a low-bandwidth silicon photonics Mach-Zehnder modulator based receiver. As the Nyquist signal has a rectangular bandwidth, it can be multiplexed in the wavelength domain without any guardband as a part of a Nyquist-WDM superchannel. These superchannels can be additionally multiplexed in space and polarization. Thus, the presented demonstration can open a new possibility for the detection of multidimensional parallel data signals with silicon photonics. No external pulse source is needed for the receiver, and frequency-time coherence is used to sample the incoming Nyquist signal with orthogonal sinc-shaped Nyquist pulse sequences. All parameters are completely tunable in the electrical domain. The feasibility of the scheme is demonstrated through a proof-of-concept experiment over the entire C-band (1530 nm–1560 nm), employing a 24 Gbaud Nyquist QPSK signal due to experimental constraints on the transmitter side electronics. However, the silicon Mach-Zehnder modulator with a 3-dB bandwidth of only 16 GHz can process Nyquist signals of 90 GHz optical bandwidth, suggesting a possibility to detect symbol rates up to 90 GBd in an integrated Nyquist receiver.</jats:p>}},
  author       = {{Misra, Arijit and Kress, Christian and Singh, Karanveer and Meier, Janosch and Schwabe, Tobias and Preussler, Stefan and Scheytt, J. Christoph and Schneider, Thomas}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{8}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Reconfigurable and real-time high-bandwidth Nyquist signal detection with low-bandwidth in silicon photonics}}},
  doi          = {{10.1364/oe.454163}},
  volume       = {{30}},
  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{47974,
  abstract     = {{Domain walls (DWs) in ferroelectric (FE) and multiferroic materials possess an ever-growing potential as integrated functional elements, for instance in optoelectronic nanodevices. Mandatory, however, is the profound knowledge of the local-scale electronic and optical properties, especially at DWs that are still incompletely characterized to date. Here, we quantify the refractive index of individual FE DWs in periodically-poled LiNbO<jats:sub>3</jats:sub> (PPLN) single crystals. When applying polarization-sensitive optical coherence tomography (PS-OCT) at 1300 nm using circular light polarization, we are able to probe the relevant electro-optical properties close to and at the DWs, including also their ordinary and extraordinary contributions. When comparing to numerical calculations, we conclude that the DW signals recorded for ordinary and extraordinary polarization stem from an increased refractive index of at least Δn &gt; 2·10<jats:sup>−3</jats:sup> that originates from a tiny region of &lt; 30 nm in width. PS-OCT hence provides an extremely valuable tool to decipher and quantify subtle changes of refractive index profiles for both inorganic and biomedical nanomaterial systems.}},
  author       = {{Golde, Jonas and Rüsing, Michael and Rix, Jan and Eng, Lukas M. and Koch, Edmund}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{21}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Quantifying the refractive index of ferroelectric domain walls in periodically poled LiNbO3 single crystals by polarization-sensitive optical coherence tomography}}},
  doi          = {{10.1364/oe.432810}},
  volume       = {{29}},
  year         = {{2021}},
}

@article{21821,
  abstract     = {{We present a combined experimental and numerical study of the far-field emission properties of optical travelling wave antennas made from low-loss dielectric materials. The antennas considered here are composed of two simple building blocks, a director and a reflector, deposited on a glass substrate. Colloidal quantum dots placed in the feed gap between the two elements serve as internal light source. The emission profile of the antenna is mainly formed by the director while the reflector suppresses backward emission. Systematic studies of the director dimensions as well as variation of antenna material show that the effective refractive index of the director primarily governs the far-field emission pattern. Below cut off, i.e., if the director’s effective refractive index is smaller than the refractive index of the substrate, the main lobe results from leaky wave emission along the director. In contrast, if the director supports a guided mode, the emission predominately originates from the end facet of the director.}},
  author       = {{Leuteritz, T. and Farheen, Henna and Qiao, S. and Spreyer, F. and Schlickriede, Christian and Zentgraf, Thomas and Myroshnychenko, Viktor and Förstner, Jens and Linden, S.}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{tet_topic_opticalantenna}},
  number       = {{10}},
  title        = {{{Dielectric travelling wave antennas for directional light emission}}},
  doi          = {{10.1364/oe.422984}},
  volume       = {{29}},
  year         = {{2021}},
}

@article{37334,
  abstract     = {{<jats:p>Uniaxial anisotropy in nonlinear birefringent crystals limits the efficiency of nonlinear optical interactions and breaks the spatial symmetry of light generated in the parametric down-conversion (PDC) process. Therefore, this effect is usually undesirable and must be compensated for. However, high gain may be used to overcome the destructive role of anisotropy in order to generate bright two-mode correlated twin-beams. In this work, we provide a rigorous theoretical description of the spatial properties of bright squeezed light in the presence of strong anisotropy. We investigate a single crystal and a system of two crystals with an air gap (corresponding to a nonlinear SU(1,1) interferometer) and demonstrate the generation of bright correlated twin-beams in such configurations at high gain due to anisotropy. We explore the mode structure of the generated light and show how anisotropy, together with crystal spacing, can be used for radiation shaping.</jats:p>}},
  author       = {{Riabinin, M. and Sharapova, Polina and Meier, Torsten}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{14}},
  pages        = {{21876--21890}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Bright correlated twin-beam generation and radiation shaping in high-gain parametric down-conversion with anisotropy}}},
  doi          = {{10.1364/oe.424977}},
  volume       = {{29}},
  year         = {{2021}},
}

@article{23476,
  author       = {{Weizel, Maxim and Scheytt, J. Christoph and Kärtner, Franz X. and Witzens, Jeremy}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Optically clocked switched-emitter-follower THA in a photonic SiGe BiCMOS technology}}},
  doi          = {{10.1364/oe.425710}},
  year         = {{2021}},
}

@article{26223,
  author       = {{Santandrea, Matteo and Stefszky, Michael and Roeland, Ganaël and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Interferometric method for determining the losses of spatially multi-mode nonlinear waveguides based on second harmonic generation}}},
  doi          = {{10.1364/oe.380788}},
  year         = {{2020}},
}

@article{21024,
  author       = {{Ansari, Vahid and Donohue, John M. and Brecht, Benjamin and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{19}},
  title        = {{{Remotely projecting states of photonic temporal modes}}},
  doi          = {{10.1364/oe.395593}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{20372,
  abstract     = {{A stepwise angular spectrum method (SASM) for curved interfaces is presented to calculate the wave propagation in planar lens-like integrated optical structures based on photonic slab waveguides. The method is derived and illustrated for an effective 2D setup first and then for 3D slab waveguide lenses. We employ slab waveguides of different thicknesses connected by curved surfaces to realize a lens-like structure. To simulate the wave propagation in 3D including reflection and scattering losses, the stepwise angular spectrum method is combined with full vectorial finite element computations for subproblems with lower complexity. Our SASM results show excellent agreement with rigorous numerical simulations of the full structures with a substantially lower computational effort and can be utilized for the simulation-based design and optimization of complex and large scale setups.}},
  author       = {{Ebers, Lena and Hammer, Manfred and Förstner, Jens}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{tet_topic_waveguides}},
  number       = {{24}},
  pages        = {{36361}},
  title        = {{{Light diffraction in slab waveguide lenses simulated with the stepwise angular spectrum method}}},
  doi          = {{10.1364/oe.409612}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{22771,
  author       = {{Stefszky, Michael and Santandrea, Matteo and vom Bruch, Felix and Krapick, S. and Eigner, Christof and Ricken, R. and Quiring, V. and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Waveguide resonator with an integrated phase modulator for second harmonic generation}}},
  doi          = {{10.1364/oe.412824}},
  year         = {{2020}},
}

@article{20157,
  author       = {{Thiele, Frederik and vom Bruch, Felix and Quiring, Victor and Ricken, Raimund and Herrmann, Harald and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Cryogenic electro-optic polarisation conversion in titanium in-diffused lithium niobate waveguides}}},
  doi          = {{10.1364/oe.399818}},
  year         = {{2020}},
}

@article{16301,
  author       = {{Atorf, Bernhard and Mühlenbernd, Holger and Zentgraf, Thomas and Kitzerow, Heinz-Siegfried}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{6}},
  pages        = {{8898--8908}},
  title        = {{{All-optical switching of a dye-doped liquid crystal plasmonic metasurface}}},
  doi          = {{10.1364/oe.383877}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{25920,
  author       = {{Padberg, Laura and Santandrea, Matteo and Rüsing, Michael and Brockmeier, Julian and Mackwitz, Peter and Berth, Gerhard and Zrenner, Artur and Eigner, Christof and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Characterisation of width-dependent diffusion dynamics in rubidium-exchanged KTP waveguides}}},
  doi          = {{10.1364/oe.397074}},
  year         = {{2020}},
}

@article{47958,
  abstract     = {{High-fidelity periodic poling over long lengths is required for robust, quasi-phase-matched second-harmonic generation using the fundamental, quasi-TE polarized waveguide modes in a thin-film lithium niobate (TFLN) waveguide. Here, a shallow-etched ridge waveguide is fabricated in x-cut magnesium oxide doped TFLN and is poled accurately over 5 mm. The high fidelity of the poling is demonstrated over long lengths using a non-destructive technique of confocal scanning second-harmonic microscopy. We report a second-harmonic conversion efficiency of up to 939 %/W (length-normalized conversion efficiency 3757 %/Wcm²), measured at telecommunications wavelengths. The device demonstrates a narrow spectral linewidth (1 nm) and can be tuned precisely with a tuning characteristic of 0.1 nm/°C, over at least 40 °C without measurable loss of efficiency.}},
  author       = {{Zhao, Jie and Rüsing, Michael and Javid, Usman A. and Ling, Jingwei and Li, Mingxiao and Lin, Qiang and Mookherjea, Shayan}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{13}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Shallow-etched thin-film lithium niobate waveguides for highly-efficient second-harmonic generation}}},
  doi          = {{10.1364/oe.395545}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{37932,
  abstract     = {{<jats:p>Hybrid quantum information processing combines the advantages of discrete and continues variable protocols by realizing protocols consisting of photon counting and homodyne measurements. However, the mode structure of pulsed sources and the properties of the detection schemes often require the use of optical filters in order to combine both detection methods in a common experiment. This limits the efficiency and the overall achievable squeezing of the experiment. In our work, we use photon subtraction to implement the distillation of pulsed squeezed states originating from a genuinely spatially and temporally single-mode parametric down-conversion source in non-linear waveguides. Due to the distillation, we witness an improvement of 0.17 dB from an initial squeezing value of −1.648 ± 0.002 dB, while achieving a purity of 0.58, and confirm the non-Gaussianity of the distilled state via the higher-order cumulants. With this, we demonstrate the source’s suitability for scalable hybrid quantum network applications with pulsed quantum light.</jats:p>}},
  author       = {{Dirmeier, Thomas and Tiedau, Johannes and Khan, Imran and Ansari, Vahid and Müller, Christian R. and Silberhorn, Christine and Marquardt, Christoph and Leuchs, Gerd}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{21}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Distillation of squeezing using an engineered pulsed parametric down-conversion source}}},
  doi          = {{10.1364/oe.402178}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{21025,
  author       = {{Eigner, Christof and Padberg, Laura and Santandrea, Matteo and Herrmann, Harald and Brecht, Benjamin and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{22}},
  title        = {{{Spatially single mode photon pair source at 800 nm in periodically poled Rubidium exchanged KTP waveguides}}},
  doi          = {{10.1364/oe.399483}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{38051,
  abstract     = {{<jats:p>The characterisation of loss in optical waveguides is essential in understanding the performance of these devices and their limitations. Whilst interferometric-based methods generally provide the best results for low-loss waveguides, they are almost exclusively used to provide characterization in cases where the waveguide is spatially single-mode. Here, we introduce a Fabry-Pérot-based scheme to estimate the losses of a nonlinear (birefringent or quasi-phase matched) waveguide at a wavelength where it is multi-mode. The method involves measuring the generated second harmonic power as the pump wavelength is scanned over the phase matching region. Furthermore, it is shown that this method allows one to infer the losses of different second harmonic spatial modes by scanning the pump field over the separated phase matching spectra. By fitting the measured phase matching spectra from different titanium indiffused lithium niobate waveguides to the model presented in this paper, it is shown that one can estimate the second harmonic losses of a single spatial-mode, at wavelengths where the waveguides are spatially multi-mode.</jats:p>}},
  author       = {{Santandrea, Matteo and Stefszky, Michael and Roeland, Ganaël and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{4}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Interferometric method for determining the losses of spatially multi-mode nonlinear waveguides based on second harmonic generation.}}},
  doi          = {{10.1364/oe.380788}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{37933,
  abstract     = {{<jats:p>We present a time-over-threshold readout technique to count the number of activated pixels from an array of superconducting nanowire single photon detectors (SNSPDs). This technique places no additional heatload on the cryostat, and retains the intrinsic count rate of the time-tagger. We demonstrate proof-of-principle operation with respect to a four-pixel device. Furthermore, we show that, given some permissible error threshold, the number of pixels that can be reliably read out scales linearly with the intrinsic signal-to-noise ratio of the individual pixel response.</jats:p>}},
  author       = {{Tiedau, Johannes and Schapeler, Timon and Anant, Vikas and Fedder, Helmut and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{4}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Single-channel electronic readout of a multipixel superconducting nanowire single photon detector}}},
  doi          = {{10.1364/oe.383111}},
  volume       = {{28}},
  year         = {{2020}},
}