@article{54544,
  abstract     = {{The biphoton correlation time, a measure for the conditional uncertainty in the temporal arrival of two photons from a photon pair source, is a key performance identifier for many quantum spectroscopy applications, with shorter correlation times typically yielding better performance. Furthermore, it provides fundamental insight into the effects of dispersion on the biphoton state. Here, we show that a characteristic dependence of the width of the temporal interferogram can be exploited to obtain insights into the amount of second-order dispersion inside the interferometer and to retrieve actual and Fourier-limited ultrashort biphoton correlation times of around 100 fs. In the presented scheme, we simultaneously measure spectral and temporal interferograms at the output of an SU(1,1) interferometer based on an integrated broadband parametric down conversion source in a Ti:LiNbO3 waveguide.}},
  author       = {{Roeder, Franz and Pollmann, René and Stefszky, Michael and Santandrea, Matteo and Luo, Kai Hong and Quiring, V. and Ricken, Raimund and Eigner, Christof and Brecht, Benjamin and Silberhorn, Christine}},
  issn         = {{2691-3399}},
  journal      = {{PRX Quantum}},
  number       = {{2}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Measurement of Ultrashort Biphoton Correlation Times with an Integrated Two-Color Broadband SU(1,1)-Interferometer}}},
  doi          = {{10.1103/prxquantum.5.020350}},
  volume       = {{5}},
  year         = {{2024}},
}

@inproceedings{61362,
  abstract     = {{<jats:p>We study the interaction of gray tracking and DC ionic conductivity in Potassium Titanyl Phosphate (KTiOPO<jats:sub>4</jats:sub>, KTP) and present a novel way to reduce conductivity via a potassium nitrate treatment improving the device quality.</jats:p>}},
  author       = {{Eigner, Christof and Padberg, Laura and Quiring, Viktor and Bocchini, Adriana and Santandrea, Matteo and Gerstmann, Uwe and Schmidt, Wolf Gero and Silberhorn, Christine}},
  booktitle    = {{CLEO 2023}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Potassium Titanyl Phosphate Material Engineering Boosting Integrated Optical Source Performance}}},
  doi          = {{10.1364/cleo_at.2023.jw2a.57}},
  year         = {{2023}},
}

@article{33484,
  abstract     = {{We study the DC conductivity in potassium titanyl phosphate (KTiOPO4, KTP) and its isomorphs KTiOAsO4 (KTA) and Rb1%K99%TiOPO4 (RKTP) and introduce a method by which to reduce the overall ionic conductivity in KTP by a potassium nitrate treatment. Furthermore, we create so-called gray tracking in KTP and investigate the ionic conductivity in theses areas. A local unintended reduction of the ionic conductivity is observed in the gray-tracked regions, which also induce additional optical absorption in the material. We show that a thermal treatment in an oxygen-rich atmosphere removes the gray tracking and brings the ionic conductivity as well as the optical transmission back to the original level. These studies can help to choose the best material and treatment for specific applications.}},
  author       = {{Padberg, Laura and Quiring, Viktor and Bocchini, Adriana and Santandrea, Matteo and Gerstmann, Uwe and Schmidt, Wolf Gero and Silberhorn, Christine and Eigner, Christof}},
  issn         = {{2073-4352}},
  journal      = {{Crystals}},
  pages        = {{1359}},
  title        = {{{DC Ionic Conductivity in KTP and Its Isomorphs: Properties, Methods for Suppression, and Its Connection to Gray Tracking}}},
  doi          = {{10.3390/cryst12101359}},
  volume       = {{12}},
  year         = {{2022}},
}

@article{26221,
  author       = {{Bartnick, Moritz and Santandrea, Matteo and Höpker, Jan Philipp and Thiele, Frederik and Ricken, Raimund and Quiring, Viktor and Eigner, Christof and Herrmann, Harald and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{2331-7019}},
  journal      = {{Physical Review Applied}},
  title        = {{{Cryogenic Second-Harmonic Generation in Periodically Poled Lithium Niobate Waveguides}}},
  doi          = {{10.1103/physrevapplied.15.024028}},
  year         = {{2021}},
}

@article{23826,
  abstract     = {{<jats:p>Potassium titanyl phosphate (KTP) is a nonlinear optical material with applications in high-power frequency conversion or quasi-phase matching in submicron period domain grids. A prerequisite for these applications is a precise control and understanding of the poling mechanisms to enable the fabrication of high-grade domain grids. In contrast to the widely used material lithium niobate, the domain growth in KTP is less studied, because many standard methods, such as selective etching or polarization microscopy, provides less insight or are not applicable on non-polar surfaces, respectively. In this work, we present results of confocal Raman-spectroscopy of the ferroelectric domain structure in KTP. This analytical method allows for the visualization of domain grids of the non-polar KTP y-face and therefore more insight into the domain-growth and -structure in KTP, which can be used for improved domain fabrication.</jats:p>}},
  author       = {{Brockmeier, Julian and Mackwitz, Peter Walter Martin and Rüsing, Michael and Eigner, Christof and Padberg, Laura and Santandrea, Matteo and Silberhorn, Christine and Zrenner, Artur and Berth, Gerhard}},
  issn         = {{2073-4352}},
  journal      = {{Crystals}},
  title        = {{{Non-Invasive Visualization of Ferroelectric Domain Structures on the Non-Polar y-Surface of KTiOPO4 via Raman Imaging}}},
  doi          = {{10.3390/cryst11091086}},
  year         = {{2021}},
}

@article{22770,
  author       = {{Gil López, Jano and Santandrea, Matteo and Roland, Ganaël and Brecht, Benjamin and Eigner, Christof and Ricken, Raimund and Quiring, Viktor and Silberhorn, Christine}},
  issn         = {{1367-2630}},
  journal      = {{New Journal of Physics}},
  title        = {{{Improved non-linear devices for quantum applications}}},
  doi          = {{10.1088/1367-2630/ac09fd}},
  year         = {{2021}},
}

@article{26889,
  author       = {{Luo, Kai Hong and Santandrea, Matteo and Stefszky, Michael and Sperling, Jan and Massaro, Marcello and Ferreri, Alessandro and Sharapova, Polina and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  title        = {{{Quantum optical coherence: From linear to nonlinear interferometers}}},
  doi          = {{10.1103/physreva.104.043707}},
  year         = {{2021}},
}

@article{26077,
  abstract     = {{<jats:p>Nonlinear SU(1,1) interferometers are fruitful and promising tools for spectral engineering and precise measurements with phase sensitivity below the classical bound. Such interferometers have been successfully realized in bulk and fiber-based configurations. However, rapidly developing integrated technologies provide higher efficiencies, smaller footprints, and pave the way to quantum-enhanced on-chip interferometry. In this work, we theoretically realised an integrated architecture of the multimode SU(1,1) interferometer which can be applied to various integrated platforms. The presented interferometer includes a polarization converter between two photon sources and utilizes a continuous-wave (CW) pump. Based on the potassium titanyl phosphate (KTP) platform, we show that this configuration results in almost perfect destructive interference at the output and supersensitivity regions below the classical limit. In addition, we discuss the fundamental difference between single-mode and highly multimode SU(1,1) interferometers in the properties of phase sensitivity and its limits. Finally, we explore how to improve the phase sensitivity by filtering the output radiation and using different seeding states in different modes with various detection strategies.</jats:p>}},
  author       = {{Ferreri, Alessandro and Santandrea, Matteo and Stefszky, Michael and Luo, Kai Hong and Herrmann, Harald and Silberhorn, Christine and Sharapova, Polina R.}},
  issn         = {{2521-327X}},
  journal      = {{Quantum}},
  title        = {{{Spectrally multimode integrated SU(1,1) interferometer}}},
  doi          = {{10.22331/q-2021-05-27-461}},
  year         = {{2021}},
}

@article{26218,
  author       = {{Santandrea, Matteo and Stefszky, Michael and Silberhorn, Christine}},
  issn         = {{2040-8978}},
  journal      = {{Journal of Optics}},
  title        = {{{General analytic theory of classical collinear three-wave mixing in a monolithic cavity}}},
  doi          = {{10.1088/2040-8986/ac0b90}},
  year         = {{2021}},
}

@inproceedings{40374,
  abstract     = {{<jats:p>We present a frequency multimode integrated SU (1,1) interferometer with a polarization converter and strong signal-idler photon correlations. Phase sensitivity below the shot noise limit is demonstrated, various filtering and seeding strategies are discussed.</jats:p>}},
  author       = {{Ferreri, A. and Santandrea, Matteo and Stefszky, Michael and Luo, Kai Hong and Herrmann, Harald and Silberhorn, Christine and Sharapova, Polina}},
  booktitle    = {{Conference on Lasers and Electro-Optics}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Multimode integrated SU(1,1) interferometer}}},
  doi          = {{10.1364/cleo_qels.2021.ftu1n.6}},
  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{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{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{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{26225,
  author       = {{Santandrea, Matteo and Stefszky, Michael and Silberhorn, Christine}},
  issn         = {{0146-9592}},
  journal      = {{Optics Letters}},
  title        = {{{General framework for the analysis of imperfections in nonlinear systems}}},
  doi          = {{10.1364/ol.44.005398}},
  year         = {{2019}},
}

@article{26226,
  author       = {{Santandrea, Matteo and Stefszky, Michael and Ansari, Vahid and Silberhorn, Christine}},
  issn         = {{1367-2630}},
  journal      = {{New Journal of Physics}},
  title        = {{{Fabrication limits of waveguides in nonlinear crystals and their impact on quantum optics applications}}},
  doi          = {{10.1088/1367-2630/aaff13}},
  year         = {{2019}},
}

@article{26237,
  author       = {{Luo, Kai-Hong and Ansari, Vahid and Massaro, Marcello and Santandrea, Matteo and Eigner, Christof and Ricken, Raimund and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Counter-propagating photon pair generation in a nonlinear waveguide}}},
  doi          = {{10.1364/oe.378789}},
  year         = {{2019}},
}

@article{26052,
  author       = {{Luo, Kai Hong and Ansari, Vahid and Massaro, Marcello and Santandrea, Matteo and Eigner, Christof and Ricken, Raimund and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Counter-propagating photon pair generation in a nonlinear waveguide}}},
  doi          = {{10.1364/oe.378789}},
  year         = {{2019}},
}

@article{26224,
  author       = {{Santandrea, Matteo and Stefszky, Michael and Roeland, Ganaël and Silberhorn, Christine}},
  issn         = {{1367-2630}},
  journal      = {{New Journal of Physics}},
  title        = {{{Characterisation of fabrication inhomogeneities in Ti:LiNbO3 waveguides}}},
  doi          = {{10.1088/1367-2630/ab5cb5}},
  year         = {{2019}},
}