@inproceedings{SchiekBaronio, author = {Schiek, Roland and Baronio, Fabio}, title = {Spatial Akhmediev Breathers in Slab Waveguides}, series = {2019 Conference on Lasers and Electro-Optics Europe European Quantum Electronics Conference (CLEO/Europe-EQEC), 23-27 June 2019, Munich, Germany}, booktitle = {2019 Conference on Lasers and Electro-Optics Europe European Quantum Electronics Conference (CLEO/Europe-EQEC), 23-27 June 2019, Munich, Germany}, doi = {10.1109/CLEOE-EQEC.2019.8872896}, abstract = {Summary form only given. The analytical breather-solutions of the Nonlinear Schr{\"o}dinger Equation (NLS) [1] have been intensively studied and verified experimentally in the time-space system of optical pulse propagation in fibers [2]. In space-space systems, i.e. in optical beam propagation breathers in ultra-fast nonlinear media have not been observed due to the breather's infinite background and a resulting extremely large power. In a lithium niobate slab waveguide with two second-harmonic (SH) resonances the resulting quasi-cubic cascaded quadratic nonlinearity provided together with the intrinsic cubic susceptibility enough nonlinearity for breather excitation at experimentally reachable powers. We could characterize the fi rst ultra -fast spatial -spatial optical breathers in a 5 -cm -long titanium indiffused lithium niobate slab waveguide at power levels down to tens of kW. The guided fundamental wave (FW) TM° fi lm mode at A = 1.32μm is phase -matched for type -I SH generation to TE 0 and TEi SH modes at temperatures near 295 and 344C. With temperature tuning the phase -mismatch and the two effective cascaded nonlinearities were adjusted. For breather observation, we aimed for a large phase -mismatch with low SH levels such that the cascaded nonlinearity is quasi -cubic and the propagation is well approximated by the NLS and its breather solutions. A frequency -doubled Nd:YAG-pumped OPA with CW-seeding delivered 5-ps long pulses with up to 200kW peak power in the waveguide. With a cylindrical telescope the beam was transformed into a very wide elliptical beam to approximate the breather background. The beam was end -fire coupled into the FW TM () mode. A variable few \% of the beam were separated and coupled with a tilt and good overlap to the main beam into the waveguide to produce a spatial modulation of the input with adjustable period and modulation depth. A beam width of 1.5mm was large enough in the compromise between available beam power and infinite beam width. A beam with a transverse modulation with periods between 130 to 300μm approximates a constant background with modulation well enough to trigger modulation instability that develops eventually into the breather.}, language = {en} } @article{SetzpfandtSolntsevTitcheneretal., author = {Setzpfandt, Frank and Solntsev, Alexander S. and Titchener, James and Wu, Che Wen and Xiong, Chunle and Schiek, Roland and Pertsch, Thomas and Neshev, Dragomir N. and Sukhorukov, Andrey A.}, title = {Tunable generation of entangled photons in a nonlinear directional coupler}, series = {Laser \& Photonics Reviews}, volume = {10}, journal = {Laser \& Photonics Reviews}, number = {1}, publisher = {WILEY-VCH}, doi = {10.1002/lpor.201500216}, pages = {131 -- 136}, abstract = {The on-chip integration of quantum light sources has enabled the realization of complex quantum photonic circuits. However, for the practical implementation of such circuits in quantum information applications, it is crucial to develop sources delivering entangled quantum photon states with on-demand tunability. Here we propose and experimentally demonstrate the concept of a widely tunable quantum light source based on spontaneous parametric down-conversion in a simple nonlinear directional coupler. We show that spatial photon-pair correlations and entanglement can be reconfigured on-demand by tuning the phase difference between the pump beams and the phase mismatch inside the structure. We experimentally demonstrate the generation of split states, robust N00N states, various intermediate regimes and biphoton steering on a single chip. Furthermore we theoretically investigate other regimes allowing all-optically tunable generation of all Bell states and flexible control of path-energy entanglement. Such wide-range capabilities of a structure comprised of just two coupled nonlinear waveguides are attributed to the intricate interplay between linear coupling and nonlinear phase matching. This scheme provides an important advance towards the realization of reconfigurable quantum circuitry.}, language = {en} } @inproceedings{Schiek, author = {Schiek, Roland}, title = {Self-phase modulation in lithium niobate waveguides}, series = {2014 International Conference Laser Optics, title=Self-phase modulation in lithium niobate waveguides, 30 June-4 July 2014, St. Petersburg, Russia}, booktitle = {2014 International Conference Laser Optics, title=Self-phase modulation in lithium niobate waveguides, 30 June-4 July 2014, St. Petersburg, Russia}, publisher = {IEEE}, doi = {10.1109/LO.2014.6886403}, abstract = {Self-phase modulation in lithium niobate wave-guides with cascaded quadratic and cubic nonlinearities is characterized by comparison of amplitude and phase of input and output pulse envelopes and spectra. Cubic nonlinear susceptibility coefficients of lithium niobate were determined from the measured nonlinear phase shifts.}, language = {en} } @inproceedings{SchiekSetzpfandtBaronio, author = {Schiek, Roland and Setzpfandt, Frank and Baronio, Fabio}, title = {Akhmediev Breathers and Modulation Instability's Growth-Decay Cycle in Slab Waveguides}, series = {Nonlinear Optics : 15-19 July 2019, Waikoloa Beach, Hawaii, United States}, booktitle = {Nonlinear Optics : 15-19 July 2019, Waikoloa Beach, Hawaii, United States}, publisher = {OSA}, address = {Washington, D.C.}, isbn = {978-1-943580-62-0}, doi = {10.1364/nlo.2019.ntu2a.2}, abstract = {Optical film waveguides served as new platform for investigating Akhmediev Breathers. Using the interplay between third-order and cascaded second-order optical nonlinearities breathers and modulation instability cycles in a wide nonlinear regime were characterized.}, language = {en} } @misc{Schiek, author = {Schiek, Roland}, title = {On the experimental ex citation of modulation instability and Akhmediev breathers}, series = {CHAOS 2020, Proceedings, 13th Chaotic Modeling and Simulation, International Conference, 9 - 12 June, 2020, Florence, Italy,}, journal = {CHAOS 2020, Proceedings, 13th Chaotic Modeling and Simulation, International Conference, 9 - 12 June, 2020, Florence, Italy,}, language = {en} } @inproceedings{Schiek, author = {Schiek, Roland}, title = {Parameter Scans for Characterization of Nonlinear Beam Propagation}, series = {Proceedings OSA Nonlinear Optics 2021: 9-13 August 2021, Washington, DC, United States}, booktitle = {Proceedings OSA Nonlinear Optics 2021: 9-13 August 2021, Washington, DC, United States}, publisher = {Optica Publishing Group, OSA}, address = {Washington, D.C.}, isbn = {978-1-943580-97-2}, doi = {10.1364/nlo.2021.ntu1b.5}, abstract = {Intensity-dependent beam propagation inside nonlinear media is difficult to characterize without cutting back — and destroying — the sample. Observing the output dependent on system parameters can provide information on the beam dynamics along the path.}, language = {en} } @article{SetzpfandtSohlerSchieketal., author = {Setzpfandt, Frank and Sohler, Wolfgang and Schiek, Roland and Pertsch, Thomas}, title = {Nonlinear coupling in discrete optical waveguide arrays with quadratic nonlinearity}, series = {Physical Review A}, volume = {92}, journal = {Physical Review A}, number = {4}, publisher = {American Physical Society}, doi = {10.1103/PhysRevA.92.043832}, abstract = {We demonstrate nonlinear coupling in a discrete optical system. This is achieved in waveguide arrays with quadratic nonlinearity, where the symmetries of the nonlinearly interacting waveguide modes are used to suppress the usually dominating nonlinear effects within individual waveguides. We derive a mathematical model to describe the nonlinear coupling in such waveguide arrays and show experimentally the profound effects of this nonlinear coupling mechanism on second-harmonic generation.}, language = {en} } @inproceedings{SetzpfandtSolntsevTitcheneretal., author = {Setzpfandt, Frank and Solntsev, Alexander S. and Titchener, James and Wu, Che Wen and Xiong, Chunle and Pertsch, Thomas and Schiek, Roland and Neshev, Dragomir N. and Sukhorukov, Andrey A.}, title = {Optically Tunable Entangled Photon State Generation in a Nonlinear Directional Coupler}, series = {Nonlinear Optics [Kauai, Hawaii 26-31 July 2015]}, booktitle = {Nonlinear Optics [Kauai, Hawaii 26-31 July 2015]}, number = {paper NW2A.4}, publisher = {OSA}, address = {Washington, D.C.}, isbn = {978-1-55752-001-2}, doi = {10.1364/nlo.2015.nw2a.4}, abstract = {We propose and experimentally demonstrate an all-optically tunable biphoton quantum light source using a nonlinear directional coupler. The source can generate high-fidelity N00N states, completely split states, and states with variable degrees of entanglement.}, language = {en} } @inproceedings{SetzpfandtSolntsevTitcheneretal., author = {Setzpfandt, Frank and Solntsev, Alexander S. and Titchener, James and Wu, Che Wen and Xiong, Chunle and Pertsch, Thomas and Schiek, Roland and Neshev, Dragomir N. and Sukhorukov, Andrey A.}, title = {Optically tunable entangled photon state generation in a nonlinear directional coupler}, series = {CLEO: QELS_Fundamental Science 2015, San Jose, California, United States, 10-15 May 2015}, booktitle = {CLEO: QELS_Fundamental Science 2015, San Jose, California, United States, 10-15 May 2015}, publisher = {OSA}, address = {Washington, D.C.}, isbn = {978-1-55752-968-8}, doi = {10.1364/cleo_qels.2015.fth4d.3}, abstract = {We propose and experimentally demonstrate an all-optically tunable biphoton quantum light source using a nonlinear directional coupler. The source can generate high-fidelity N00N states, completely split states, and states with variable degrees of entanglement.}, language = {en} } @inproceedings{SchiekSetzpfandtPertschetal., author = {Schiek, Roland and Setzpfandt, Frank and Pertsch, Thomas and Baronio, Fabio and de Angelis, Costantino}, title = {Spatial Rogue Waves in Quadratic Optical Slab Waveguides}, series = {Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), OSA Techncail Digest (online) (Optica Publishing Group, 2018), paper NpTh1H.7}, booktitle = {Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), OSA Techncail Digest (online) (Optica Publishing Group, 2018), paper NpTh1H.7}, publisher = {OSA}, address = {Washington D.C.}, isbn = {978-1-943580-43-9}, doi = {10.1364/np.2018.npth1h.7}, abstract = {Spatial optical breather solutions of the Nonlinear Schr{\"o}dinger Equation have been observed for the first time. The experiment was performed in an optical slab waveguide with the cascaded quadratic nonlinearity in second-harmonic generation.}, language = {en} } @inproceedings{SetzpfandtSchiekSohleretal., author = {Setzpfandt, Frank and Schiek, Roland and Sohler, Wolfgang and Pertsch, Thomas}, title = {Nonlinear Nearest-Neighbor Coupling in Quadratic Waveguide Arrays}, series = {Nonlinear Optics : Proceedings Nonlinear Optics 26-31 July 2015, Kauai, Hawaii, United States}, booktitle = {Nonlinear Optics : Proceedings Nonlinear Optics 26-31 July 2015, Kauai, Hawaii, United States}, publisher = {OSA}, address = {Washington, D.C.}, isbn = {978-1-55752-001-2}, doi = {10.1364/nlo.2015.nm3b.6}, abstract = {We investigate nonlinear coupling between neighboring waveguides in waveguide arrays with second-order nonlinearity. Using mode symmetries to suppress local nonlinearities, we experimentally show the profound effect of such nonlinear nearest-neighbor interactions on second-harmonic generation.}, language = {en} } @article{SchiekSolntsevNeshev2025, author = {Schiek, Roland and Solntsev, Alexander S. and Neshev, Dragomir N.}, title = {Measurement of the cubic nonlinear susceptibility in lithium niobate}, series = {Optical Materials Express}, volume = {15}, journal = {Optical Materials Express}, number = {5}, publisher = {Optica Publishing Group}, issn = {2159-3930}, doi = {10.1364/OME.557516}, pages = {1100 -- 1117}, year = {2025}, abstract = {We measured the cubic nonlinear susceptibility tensor elements ( χ(3)) for polarization along the primary crystallographic axis in titanium-indiffused lithium niobate waveguides, assessed through self-phase modulation using picosecond-duration pulses at telecommunication wavelengths. A dominant, highly temperature- and wavelength-dependent contribution from a cascaded second-order nonlinearity is observed. Through careful extraction of the cascaded effect, we quantify the intrinsic third-order susceptibility tensor elements as χ(3) zzzz(ω; ω, ω, -ω) = (5.2 ± 1.3) × 10-21 m2 V2 and χ(3) xxxx(ω; ω, ω, -ω) = χ(3) yyyy(ω; ω, ω, -ω) = (3.6 ± 0.8) × 10-21 m2 V2 . These measurements underscore the substantial impact of the cascaded nonlinearity in enhancing the effective cubic nonlinearity in lithium niobate and offer precise values essential for the design of nonlinear photonic devices.}, language = {en} }