© The Author(s) 2018. Integrated photonics is a leading platform for quantum technologies including nonclassical state generation 1, 2, 3, 4, demonstration of quantum computational complexity 5 and secure quantum communications 6. As photonic circuits grow in complexity, full quantum tomography becomes impractical, and therefore an efficient method for their characterization 7, 8 is essential. Here we propose and demonstrate a fast, reliable method for reconstructing the two-photon state produced by an arbitrary quadratically nonlinear optical circuit. By establishing a rigorous correspondence between the generated quantum state and classical sum-frequency generation measurements from laser light, we overcome the limitations of previous approaches for lossy multi-mode devices 9, 10. We applied this protocol to a multi-channel nonlinear waveguide network and measured a 99.28±0.31% fidelity between classical and quantum characterization. This technique enables fast and precise evaluation of nonlinear quantum photonic networks, a crucial step towards complex, large-scale, device production.

© 2017 Optical Society of America. Photonic systems such as arrays of coupled waveguides are well suited to emulating quantum mechanics with periodic lattice potentials, allowing the investigation of many physical phenomena in a convenient experimental setting. Usually, photons will 'hop only between neighboring lattice sites at a rate given by a purely real coupling coefficient, thus limiting the rich physics enabled by long-range coupling with complex coupling coefficients. Here we suggest and experimentally realize a spectral photonic lattice that can be configured to realize a wide variety of complex-valued coupling parameters over arbitrary lattice separations. In this system, a weak signal propagates across discrete frequency channels, driven by nonlinear interaction from stronger pump lasers. Our approach allows the experimental investigation of new discrete lattice physics-as an example, we demonstrate two novel instances of the discrete Talbot effect.

© 2017 The Author(s). Spontaneous parametric down-conversion (SPDC) is a widely used method to generate entangled photons, enabling a range of applications from secure communication to tests of quantum physics. Integrating SPDC on a chip provides interferometric stability, allows to reduce a physical footprint, and opens a pathway to true scalability. However, dealing with different photon polarizations and wavelengths on a chip presents a number of challenging problems. In this work, we demonstrate an on-chip polarization beam-splitter based on z-cut titanium-diffused lithium niobate asymmetric adiabatic couplers (AAC) designed for integration with a type-II SPDC source. Our experimental measurements reveal unique polarization beam-splitting regime with the ability to tune the splitting ratios based on wavelength. I n particular, we measured a splitting ratio of 17 dB over broadband regions ( > 60 nm) for both H-and V-polarized lights and a specific 50%/50% splitting ratio for a cross-polarized photon pair from the AAC. The results show that such a system can be used for preparing different quantum polarization-path states that are controllable by changing the phase-matching conditions in the SPDC over a broad band. Furthermore, we propose a fully integrated electro-optically tunable type-II SPDC polarization-path-entangled state preparation circuit on a single lithium niobate photonic chip.

© CopyrightEPLA, 2017. We establish theoretically and demonstrate experimentally that photon-pair generation through spontaneous parametric down-conversion in a nonlinear waveguide with scattering or material losses can be effectively emulated by classical laser light propagation through a specially designed linear waveguide circuit. This platform can represent arbitrary photon and pump losses, with a potential for the emulation of non-Markovian decay. We characterize the photon-pair correlation spectrum and observe its characteristic transformation from the well-known sinc-shape in lossless waveguides towards a Lorentzian shape in the presence of photon loss.

© 2016 The Authors Photon entanglement has a range of applications from secure communication to the tests of quantum mechanics. Utilizing optical nonlinearity for the generation of entangled photons remains the most widely used approach due to its quality and simplicity. The on-chip integration of entangled light sources has enabled the increase of complexity and enhancement of stability compared to bulk optical implementations. Entanglement over different optical paths is uniquely suited for photonic chips, since waveguides are typically optimized for particular wavelength and polarization, making polarization- and frequency-entanglement less practical. In this review we focus on the latest developments in the field of on-chip nonlinear path-entangled photon sources. We provide a review of recent implementations and compare various approaches to tunability, including thermo-optical, electro-optical and all-optical tuning. We also discuss a range of important technical issues, in particular the on-chip separation of the pump and generated entangled photons. Finally, we review different quality control methods, including on-chip quantum tomography and recently discovered classical-quantum analogy that allows to characterize entangled photon sources by performing simple nonlinear measurements in the classical regime.

© 2017 Author(s). Nonlinear optical waveguides enable the integration of entangled photon sources and quantum logic gates on a quantum photonic chip. One of the major challenges in such systems is separating the generated entangled photons from the pump laser light. In this work, we experimentally characterize double-N-shaped nonlinear optical adiabatic couplers designed for the generation of spatially entangled photon pairs through spontaneous parametric down-conversion, while simultaneously providing spatial pump filtering and keeping photon-pair states pure. We observe that the pump photons at a wavelength of 671 nm mostly remain in the central waveguide, achieving a filtering ratio of over 20 dB at the outer waveguides. We also perform classical characterization at the photon-pair wavelength of 1342 nm and observe that light fully couples from an input central waveguide to the outer waveguides, showing on chip separation of the pump and the photon-pair wavelength.

Recent progress in the study of resonant light confinement in high-index dielectric nanostructures suggests a new route for achieving efficient control of both electric and magnetic components of light. It also leads to the enhancement of nonlinear effects near electric and magnetic Mie resonances with an engineered radiation directionality. Here we study the third-harmonic generation from dimers composed of pairs of two identical silicon nanoparticles and demonstrate, both numerically and experimentally, that the multipolar harmonic modes generated by the dimers near the Mie resonances allow the shaping of the directionality of nonlinear radiation.

The quest for nanoscale light sources with designer radiation patterns and polarization has motivated the development of nanoantennas that interact strongly with the incoming light and are able to transform its frequency, radiation, and polarization patterns. Here, we demonstrate dielectric AlGaAs nanoantennas for efficient second harmonic generation, enabling the control of both directionality and polarization of nonlinear emission. This is enabled by specialized III-V semiconductor nanofabrication of high-quality AlGaAs nanostructures embedded in optically transparent low-index material, thus allowing for simultaneous forward and backward nonlinear emission. We show that the nanodisk AlGaAs antennas can emit second harmonic in preferential direction with a backward-to-forward ratio of up to five and can also generate complex vector polarization beams, including beams with radial polarization.

Nonlinear optical nanoscale waveguides are a compact and powerful platform for efficient wavelength conversion. The free-standing waveguide geometry opens a range of applications in microscopy for local delivery of light, where in situ wavelength conversion helps to overcome various wavelength-dependent issues, such as biological tissue damage. In this paper, we present an original patterning method for high-precision fabrication of free-standing nanoscale waveguides based on lithium niobate, a material with a strong second-order nonlinearity and a broad transparency window covering the visible and mid-infrared wavelength ranges. The fabrication process combines electron-beam lithography with ion-beam enhanced etching and produces nanowaveguides with lengths from 5 to 50 m, widths from 50 to 1000 nm and heights from 50 to 500 nm, each with a precision of few nanometers. The fabricated nanowaveguides are tested in an optical characterization experiment showing efficient second-harmonic generation.

We propose and demonstrate a novel type of optical integrated structure consisting of three adiabatically coupled waveguides arranged in an N-shaped geometry. Unlike conventional adiabatic three-waveguide couplers mimicking the stimulated Raman adiabatic passage process which utilize solely the counter-intuitive coupling and, thus, operate only in one direction, our structure achieves complete bidirectional light transfer between two waveguides through the counter-intuitive and intuitive coupling in either direction over a wide wavelength range. Moreover, the light transfer through the intuitive coupling is more efficient and robust than through the counter-intuitive coupling.

In spontaneous parametric downconversion (SPDC), a pump photon spontaneously splits into signal and idler photons in media with quadratic nonlinearity. This phenomenon is the most widely utilized source of entangled photons with multiple applications in quantum information technology. SPDC on a chip is usually treated as a local process, meaning that signal and idler photons are created in the same position at which the pump photon is destroyed. We reveal that this locality condition can be violated in an array of coupled waveguides. By utilizing higher-order modes of individual waveguides, it is possible to destroy a pump photon in one waveguide and to generate signal and idler photons in other waveguides. This phenomenon of nonlocal photon-pair generation opens new opportunities for the engineering of spatial photon entanglement.

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA. 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 inf ormation 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. An integrated all-optically tunable source of two-photon quantum states based on spontaneous parametric down-conversion is experimentally demonstrated in a directional coupler consisting of two lithium niobate waveguides. The degree of entanglement and shape of two-photon spatial correlations is widely tunable by varying the phase mismatch and relative phases of the two pump beams. The operating principle is suitable for practical implementation of reconfigurable photon sources in on-chip quantum circuits.

We present an approach to quantum tomography based on first expanding a quantum state across extra degrees of freedom and then exploiting the introduced sparsity to perform reconstruction. We formulate its application to photonic circuits and show that measured spatial photon correlations at the output of a specially tailored discrete-continuous quantum walk can enable full reconstruction of any two-photon spatially entangled and mixed state at the input. This approach does not require any tunable elements, so it is well suited for integration with on-chip superconducting photon detectors.

© 2015 Optical Society of America. We describe the process of parametric amplification in a directional coupler of quadratically nonlinear and lossy waveguides, which belongs to a class of optical systems with spatial parity-time (PT) symmetry in the linear regime. We identify a distinct spectral PT anti-symmetry associated with optical parametric interaction, and show that pumpcontrolled symmetry breaking can facilitate spectrally selective mode amplification in analogy with PT lasers. We also establish a connection between the breaking of spectral and spatial mode symmetries, revealing the potential to implement unconventional regimes of spatial light switching through ultrafast control of PT breaking by pump pulses.

© 2015 American Physical Society. We analyze spontaneous parametric down-conversion in various experimentally feasible one-dimensional quadratic nonlinear waveguide arrays, with emphasis on the relationship between the lattice's topological invariants and the biphoton correlations. Nontrivial topology results in a nontrivial "winding" of the array's Bloch waves, which introduces additional selection rules for the generation of biphotons, independent of existing control using the pump beam's spatial profile and phase-matching conditions. In finite lattices, nontrivial topology produces single-photon edge modes, resulting in "hybrid" biphoton edge modes, with one photon localized at the edge and the other propagating into the bulk. When the single-photon band gap is sufficiently large, these hybrid biphoton modes reside in a band gap of the bulk biphoton Bloch wave spectrum. Numerical simulations support our analytical results.

© 2015 American Chemical Society. We experimentally demonstrate practical approaches to enhance second-harmonic (SH) generation in individual lithium niobate nanowires (NWs) with a sub-micrometer cross-section and length up to tens of micrometers. We establish that parametric interactions of guided modes propagating along the NW determine the SH output power, which can be therefore controlled by the NW length. We show that the SH power is increased by about 84 times at wavelengths corresponding to modal phase-matching. Importantly, at non-phase-matched wavelengths the SH power can be improved by a factor of up to 9.3 by adjusting the NW length with a focused ion beam. We also characterize SH emission directionality, which can be further tailored for applications in integrated optical circuits and nonlinear microscopy.

© 2015 American Physical Society. ©2015 American Physical Society. We study cascaded harmonic generation of hybrid surface plasmons in integrated planar waveguides composed of a graphene layer and a doped-semiconductor slab. We derive a comprehensive model of cascaded third-harmonic generation through phase-matched nonlinear interaction of fundamental, second-harmonic, and third-harmonic plasmonic modes supported by the structure. We show that hybrid graphene-semiconductor waveguides can simultaneously phase-match these three interacting harmonics, increasing the total third-harmonic output by a factor of 5 compared to the noncascaded regime.

We predict analytically and confirm with numerical simulations that intermode dispersion in nanowire waveguide arrays can be tailored through periodic waveguide bending, facilitating flexible spatiotemporal reshaping without breakup of femtosecond pulses. This approach allows simultaneous and independent control of temporal dispersion and spatial diffraction that are often strongly connected in nanophotonic structures.

© 2015 Astro Ltd. We develop a technique for detailed analysis of aperiodically poled crystalline nonlinear transfer functions. The method allows precise evaluation of 1D aperiodic domain structure amplitude spectra. It also allows determining the angle of periodic poling in respect to the crystalline z axis, as well as the dispersion of both ordinary and extraordinary refractive indexes in a broad spectral range. The measurement is non-destructive, and all data can be extracted from two frequency-angular spontaneous parametric down-conversion (SPDC) spectra. The precision of the domain structure analysis for aperiodically poled lithium niobate is increased by an order of magnitude in comparison to previously reported techniques based on spontaneous parametric down-conversion.

© 2015 American Physical Society. ©2015 American Physical Society. We predict that all-optically-reconfigurable generation of photon pairs with tailored spatial entanglement can be realized via spontaneous parametric down conversion in integrated nonlinear coupled waveguides. The required elements of the output quantum wave function are directly mapped from the amplitudes and phases of the classical laser pump inputs in each waveguide. This is achieved through special nonuniform domain poling, which locally inverts the sign of quadratic nonlinear susceptibility and accordingly shapes the interference of biphoton quantum states generated along the waveguides. We demonstrate a device configuration for the generation of any linear combination of two-photon Bell states.

© 2014 American Physical Society. We describe theoretically the process of spontaneous parametric down-conversion in quadratic nonlinear waveguide arrays in the presence of linear loss. We derive a set of discrete Schrödinger-type equations for the biphoton wave function and the wave function of one photon when the other photon in a pair is lost. We demonstrate effects arising from loss-affected interference between the generated photon pairs and show that nonlinear waveguide arrays can serve as a robust loss-tolerant integrated platform for the generation of entangled photon states with nonclassical spatial correlations.

We describe spontaneous parametric down-conversion of a single-photon pump in quadratic nonlinear waveguides and waveguide arrays, taking into account spectral broadening of the signal and idler photons. We perform a detailed analysis of the photon-pair intensities, spectra and spatial correlations for different types of phase-matching conditions and identify suppression of Rabi-like oscillations due to spectral dispersion. We also discuss distinct features of signal and idler photon correlations related to the single-photon nature of the pump. © 2014 Elsevier B.V.

We study experimentally and theoretically the temporal dynamics of laser pulses propagating under conditions of spatial self-focusing in quadratic nonlinear waveguide arrays made from periodically poled lithium niobate. We observed temporal pulse breakup and temporal pulse narrowing and studied the dynamics of these effects in different waveguides. We investigated the influence of the frequency dependence of the mode indices as a limiting factor for soliton formation. Our experimental results are in good agreement with the theoretical model developed from coupled-mode theory, providing a detailed understanding of pulse dynamics and beam distribution in waveguide arrays with quadratic nonlinearity. © 2014 American Physical Society.

We demonstrate a nonlinear optical chip that generates photons with reconfigurable nonclassical spatial correlations. We employ a quadratic nonlinear waveguide array, where photon pairs are generated through spontaneous parametric down-conversion and simultaneously spread through quantum walks between the waveguides. Because of the quantum interference of these cascaded quantum walks, the emerging photons can become entangled over multiple waveguide positions. We experimentally observe highly nonclassical photon-pair correlations, confirming the high fidelity of on-chip quantum interference. Furthermore, we demonstrate biphoton-state tunability by spatial shaping and frequency tuning of the classical pump beam.

We derive general coupled-mode equations describing the nonlinear interaction of electromagnetic modes in periodic media with loss and gain. Our approach is rigorously based on the Lorentz reciprocity theorem, and it can be applied to a broad range of metal-dielectric photonic structures, including plasmonic waveguides and metamaterials. We verify that our general results agree with the previous analysis of particular cases, and predict novel effects on self- and cross-phase modulation in multilayer nonlinear fishnet metamaterials.

We propose a novel integrated scheme for generation of Bell states, which allows simultaneous spatial filtering of pump photons. It is achieved through spontaneous parametric down-conversion in the system of nonlinear adiabatically coupled waveguides. We perform detailed analytic study of photon-pair generation in coupled waveguides and reveal the optimal conditions for the generation of each particular Bell state. Furthermore, we simulate the performance of the device under realistic assumptions and show that adiabatic coupling allows us to spatially filter the pump from modal-entangled photon pairs. Finally, we demonstrate that adiabatic couplers open the possibility of maintaining the purity of generated Bell states in a relatively fabrication-fault-tolerant way. © 2014 Optical Society of America.

We suggest that closed-loop quadratic nonlinear waveguide arrays can be used as a compact interferometrically stable integrated source of discrete orbital-angular-momentum (OAM) entangled biphoton state. We describe analytically and numerically the process of biphoton generation through spontaneous parametric down-conversion in triangular waveguide arrays, and reveal that the generated biphoton quantum states can be precisely controlled by changing the pump phase and wavelength, including the case of photon-pair generation with pure OAM. © 2013 American Physical Society.

We study the nonlinear optical properties of lithium niobate (LiNbO(3)) nanowires (NWs) fabricated by a top-down ion beam enhanced etching method. First, we demonstrate generation and propagation of the second-harmonic (SH) light in LiNbO(3) NWs of typical rectangular cross-sections of 400 x 600 nm(2) and length from 10 to 50 m. Then, we show local fluorescent excitation of 4',6-diamidino-2-phenylindole (DAPI) dye with the propagated SH signal in standard concentrations as for biological applications. By measuring the detected average power of the propagated fundamental harmonic (FH) and the SH signal at the output of the NWs, we directly prove the dominating role of the SH signal over possible two-photon excitation processes with the FH in the DAPI dye. We estimate that 63 ± 6 pW of the propagated SH average power is required for detectable dye excitation. Finally, we model the waveguiding of the SH light to determine the smallest NW cross-section (around 40x60 nm(2)) which is potentially able to excite fluorescence with a FH intensity below the cell damage threshold.

We show that classical light diffraction in arrays of specially modulated coupled optical waveguides can simulate the quantum process of two-mode squeezing in nonlinear media, with the waveguide mode amplitudes corresponding the signal and idler photon numbers. The whole Fock space is mapped by a set of arrays, where each array represents the states with a fixed difference between the signal and idler photon numbers. We demonstrate a transition from photon number growth to Bloch oscillations with periodical revivals of an arbitrary input state, associated with an increase of the effective phase mismatch between the pump and the squeezed photons. © 2013 American Physical Society.

Quantum entanglement became essential in understanding the non-locality of quantum mechanics. In optics, this non-locality can be demonstrated on impressively large length scales, as photons travel with the speed of light and interact only weakly with their environment. Spontaneous parametric down-conversion (SPDC) in nonlinear crystals provides an efficient source for entangled photon pairs, so-called biphotons. However, SPDC can also be implemented in nonlinear arrays of evanescently coupled waveguides which allows the generation and the investigation of correlated quantum walks of such biphotons in an integrated device. Here, we analytically and experimentally demonstrate that the biphoton degrees of freedom are entailed in an additional dimension, therefore the SPDC and the subsequent quantum random walk in one-dimensional arrays can be simulated through classical optical beam propagation in a two-dimensional photonic lattice. Thereby, the output intensity images directly represent the biphoton correlations and exhibit a clear violation of a Bell-like inequality.

We study the temporal dynamics of all-optical switching in nonlinear directional couplers in periodically poled lithium niobate. The characteristic features of such switching, including asymmetric pulse break-up and back-switching were measured in full agreement with the theoretical predictions. Based on the time-resolved measurement of intensity-dependent switching, finally the theoretically long-known continuous-wave switching curve has experimentally been confirmed. © 2012 American Institute of Physics.

We suggest an application of pump-degenerate four-wave mixing process in tapered waveguides for generation of ultrashort pulses with central frequency tunable over the material transparency range. Our method can produce strongly compressed frequency-converted pulses in presence of group-velocity mismatch and group-velocity dispersion. Additionally, the proposed technique does not require pulse phase synchronization and effectively operates for strongly chirped pump pulses, thus enabling the use of longer nonlinear media for high conversion efficiency. © 2012 Optical Society of America.

We analyze the process of photon-pair generation with simultaneous quantum walks in a quadratic nonlinear waveguide array. We demonstrate that the spontaneous parametric down-conversion in the array allows for creating quantum states with strongly pronounced spatial correlations, which are qualitatively different from those possible in bulk crystals or through quantum walks in linear waveguide arrays. Most importantly, the photon correlations can be controlled entirely classically by varying the spatial profile of the pump beam or the phase-matching conditions.

We study experimentally and numerically the dynamics of a recently found topological phase transition for discrete quadratic solitons with linearly coupled SH waves. We find that, although no stationary states are excited in the experimental situation, the generic feature of the phase transition of the SH is preserved. By utilizing simulations of the coupled mode equations we identify the complex processes leading to the phase transition involving spatial focusing and the generation of new frequency components. These distinct signatures of the dynamic phase transition are also demonstrated experimentally.

We predict highly efficient third harmonic generation through simultaneous phase-matching of second-harmonic generation and sum-frequency generation in lithium niobate nanowaveguides, enabled due to strong modal dispersion. We demonstrate that the waveguide size which corresponds to phase-matching is also optimal for highest mode confinement and therefore for strongly enhanced conversion efficiency. © 2011 American Institute of Physics.

We present a method of measurement of the extraordinary refractive index dispersion in MIR for periodically and aperiodically poled nonlinear crystals with unknown or uncertain periods. The method is based on the spontaneous parametric down-conversion and is useful for the crystals with domain structure formed directly in the process of growth by Czochralski technique. As an example we measure the extraordinary refractive index of in-growth poled 2 mol% Mg and 1 mol% Nd doped congruent lithium niobate and present the corresponding Sellmeier equation in the range of 0.4-3.6 m. © 2010 Springer-Verlag.

We describe a method of ultrashort-pulse and ultrafast-pulse-train generation through optical parametric amplification of a laser beat wave. Numerical simulation shows that 250-fs laser pulses at 1.55 m are generated from a beat-wave seeded optical parametric amplifier pumped by a 30-ps laser at 1064 nm. The pulse compression is attributable to sideband generation and parametric amplification under group velocity mismatch. Our experimental result confirms efficient generation of comb-like sidebands for the mixing waves from such an optical parametric amplifier. © 2009 Elsevier B.V. All rights reserved.

© OSA 2017. We suggest and realize experimentally quantum walks on a spectral photonic lattice with optically tunable long-range and complex hopping coefficients facilitated by nonlinear parametric interactions, enabling asymmetric frequency shaping and Talbot effect with arbitrary periodicity.

© 2017 IEEE. We demonstrate enhanced second-harmonic generation from a monolayer MoSe 2 through Si waveguide integration. This is achieved by exciting the monolayer through the guided mode, which dramatically increases the interaction length and allows for phasematching.

© OSA 2017. We demonstrate enhanced second-harmonic generation from a monolayerMoSe2 through Si waveguide integration. This is achieved by exciting the monolayer through the guided mode, which dramatically increases the interaction length and allows for phasematching.

© 2017 Institute of Electrical and Electronics Engineers Inc. All rights reserved. We propose and demonstrate a new method for the characterization of nonlinear multimode integrated devices that reconstruct the biphoton state produced trough spontaneous parametric down-conversion (SPDC) using classical sum-frequency generation measurements. The proposed method is experimentally demonstrated by predicting the state generated from a multi-channel integrated nonlinear waveguide device.

©2017 IEEE We demonstrate experimentally sum-frequency generation in AlGaAs nano-resonators, establishing a quantum-classical correspondence with spontaneous parametric down-conversion. We predict that AlGaAs nano-resonators can be utilized as high-rate sources of photon pairs with non-classical correlations.

© 2017 Institute of Electrical and Electronics Engineers Inc. All Rights Reserved. We fabricate AlGaAs nanoantennas on a glass substrate and demonstrate the highest nonlinear conversion efficiency of 10 -4 with the capability for shaping the radiation patterns and polarization of the second harmonic emission in both forward and backward directions. We also decode dynamic multipolar contributions to the second harmonic generation within such nanoantennas.

©2017 IEEE We demonstrate experimentally on-chip-integrated quantum spectroscopy by generating biphotons in a LiNbO 3 waveguide through spontaneous parametric down-conversion, and using signal photon detection in the NIR to study the dynamics of idler photons in the MIR.

© 2017 IEEE. We formulate a method of quantum tomography that scales linearly with the number of photons and involves only one optical transformation. We demonstrate it experimentally for two-photon entangled states using a special photonic chip.

© 2017 IEEE. We suggest and realize experimentally dielectric metasurfaces with high transmission efficiency for quantum multi-photon tomography, allowing for full reconstruction of pure or mixed quantum polarization states across a broad bandwidth.

© OSA 2017. We suggest and realize experimentally dielectric metasurfaces with high transmission efficiency for quantum multi-photon tomography, allowing for full reconstruction of pure or mixed quantum polarization states across a broad bandwidth.

© OSA 2017. We measure the complex weak value beyond the weak interaction regime between the measurement apparatus and the measured photon wavefunction based on the direct measurement scheme.

© 2016 OSA.We fabricate AlGaAs nanodisk antennas on a glass substrate and demonstrate experimentally the shaping of radiation patterns and polarization of the second harmonic emission in both forward and backward directions.

© OSA 2016.We fabricate AlGaAs nanodisk antennas on a glass substrate and demonstrate experimentally the shaping of radiation patterns and polarization of the second harmonic emission in both forward and backward directions.

© OSA 2016.We fabricate AlGaAs nanodisk antennas on a glass substrate and demonstrate experimentally the shaping of radiation patterns and polarization of the second harmonic emission in both forward and backward directions.

© 2016 OSA.We demonstrate a coupled-waveguide platform which realizes classical optical simulation of quantum photon-pair generation through spontaneous parametric down-conversion in a nonlinear lossy waveguide. The photon-pair creation vs. the phase mismatch and loss are experimentally mapped.

© 2016 OSA.We present the realization of an inhomogeneously poled nonlinear waveguide array for the generation of photon pairs. The device is characterized by coincidence counting and a novel method based on reversed sum-frequency generation measurements.

© 2016 OSA.We present the realization of an inhomogeneously poled nonlinear waveguide array for the generation of photon pairs with integrated pump filtering. The biphoton wave-function produced from the device is characterized using reversed sum-frequency generation measurements.

© 2016 OSA.We predict highly efficient sum-frequency conversion in quadratic nonlinear dielectric nano-resonators made of AlGaAs, and formulate a general quantum-classical correspondence with spontaneous parametric down-conversion, revealing a photon-pair generation regime with non-classical angular correlations.

© 2016 OSA.We predict and demonstrate experimentally a metal-insulator phase transition from extended wave transport to localized Bloch oscillations at a critical effective potential strength in photonic lattices, which realize optical emulator of quantum photon squeezing.

© OSA 2016. We formulate a method of quantum tomography that scales linearly with the number of photons and involves only one optical transformation. We demonstrate it experimentally for twophoton entangled states using a special photonic chip.

© 2016 OSA.We present a novel approach for all-optically reconfigurable integrated generation of quantum entangled photons in cluster states through spontaneous parametric down-conversion in coupled arrays of quadratic nonlinear waveguides with special poling patterns.

© 2016 OSA.We demonstrate a controllable non-reciprocity via in-band transitions of photons mediated by second-order parametric nonlinear processes, and propose a dynamic optical isolator based on directional geometric phase-shifts controlled by a single pump.

© 2015 SPIE. We describe the process of parametric amplification in a directional coupler of quadratically nonlinear and lossy waveguides, which belong to a class of optical systems with spatial parity-time (PT) symmetry in the linear regime. We identify a distinct spectral parity-time anti-symmetry associated with optical parametric interactions, and show that pump-controlled symmetry breaking can facilitate spectrally selective mode amplification in analogy with PT lasers. We also establish a connection between breaking of spectral and spatial mode symmetries, revealing the potential to implement unconventional regimes of spatial light switching through ultrafast control of PT breaking by pump pulses.

© 2015 OSA. We predict that directional coupler of quadratically nonlinear and lossy waveguides can perform ultrafast signal switching and parametric amplification, using the pump-controlled breaking of the parity-time anti-symmetry associated with nonlinear wave mixing.

We predict that directional coupler of quadratically nonlinear and lossy waveguides can perform ultrafast signal switching and parametric amplification, using the pump-controlled breaking of the parity-time anti-symmetry associated with nonlinear wave mixing. © 2014 Optical Society of America.

© 2015 OSA. We predict that directional coupler of nonlinear and lossy waveguides can perform ultrafast signal switching and parametric amplification, using the pump-controlled breaking of the parity-time anti-symmetry associated with nonlinear wave mixing.

We describe the process of parametric amplification in a directional coupler of quadratically nonlinear and lossy waveguides, which belongs to a class of optical systems with spatial parity-time (PT) symmetry in the linear regime. We identify a distinct spectral PT anti-symmetry associated with optical parametric interaction, and show that pump-controlled symmetry breaking can facilitate spectrally selective mode amplification in analogy with PT lasers. We also establish a connection between the breaking of spectral and spatial mode symmetries, revealing the potential to implement unconventional regimes of spatial light switching through ultrafast control of PT breaking by pump pulses.

© 2015 OSA. Cubic and quadratic nonlinear susceptibility tensor elements in lithium niobate waveguides and optical fibers were determined from measurements of pulse envelopes and power-dependent phase-changes due to self-phase modulation.

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. © 2014 Optical Society of America.

© 2015 OSA. 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.

© 2015 OSA. 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.

We predict that complete deterministic conversion of one to two photons can be achieved at a finite propagation distance in specially engineered nonlinear waveguides, by designing quantum frequency mixing across a broad range of frequencies. © 2014 Optical Society of America.

© OSA 2015. We show that special domain poling patterns in arrays of coupled nonlinear waveguides can allow shaping of the photon pair wavefunction produced by down-conversion. This allows pump filtering and the reconfigurable generation of Bell states.

© OSA 2016. We present the realization of an inhomogeneously poled nonlinear waveguide array for the generation of photon pairs. The device is characterized by coincidence counting and a novel method based on reversed sum-frequency generation measurements.

© 2014 Optical Society of America. We have generated second-harmonic (SH) signal in lithium niobate (LiNbO 3 ) nanowires (NWs) to locally excite fluorescent dye in typical cell staining concentration. We show the second-order behavior of the SH signal in a NW with cross-section of 400x600 nm 2 . A guided SH power of 63±6 pW is needed to detect dye excitation in a 1 g/ml DAPI dye solution. We also perform simulations to define that the LiNbO 3 NWs with cross-sections down to 40x60nm2 are potentially able to produce the threshold amount of the SH power.

We have generated second-harmonic (SH) signal in lithium niobate (LiNbO 3 ) nanowires (NWs) to locally excite fluorescent dye in typical cell staining concentration. We show the second-order behavior of the SH signal in a NW with cross-section of 400x600 nm 2 . A guided SH power of 63±6 pW is needed to detect dye excitation in a 1 g/ml DAPI dye solution. We also perform simulations to define that the LiNbO 3 NWs with cross-sections down to 4060nm 2 are potentially able to produce the threshold amount of the SH power. © 2014 OSA.

© OSA 2016. We predict photon-pair generation with non-classical angular correlations through spontaneous parametric down-conversion in quadratic nonlinear dielectric AlGaAs nanoresonators, and establish a quantum-classical correspondence with sum-frequency conversion.

© 2014 Optical Society of America. We show how classical light can be used to simulate a nonclassical quantum process. Specially modulated optical waveguides were utilized to emulate two-mode squeezed vacuum states as the light amplitudes in our arrays correspond to the photon number distribution of the squeezed states. In our experiments demonstrate a transition from photon number growth to periodic Bloch oscillations for increased phase mismatch.

We show how classical light can be used to simulate a nonclassical quantum process. Specially modulated optical waveguides were utilized to emulate two-mode squeezed vacuum states as the light amplitudes in our arrays correspond to the photon number distribution of the squeezed states. In our experiments demonstrate a transition from photon number growth to periodic Bloch oscillations for increased phase mismatch. © 2014 Optical Society of America.

© 2014 OSA. We propose special poling of quadratic nonlinear waveguide arrays enabling generation of photon pairs in any path entangled quantum state. Real-time switching between output quantum states can be achieved by varying classical input laser amplitudes.

We propose a design for an integrated photonic circuit capable of generating photon pairs in any path entangled quantum state. Real-time switching between output quantum states can be achieved by varying classical input lasers. © 2014 Engineers Australia.

We propose a novel integrated scheme for the generation of Bell states, which allows simultaneous spatial filtering of pump photons. It is achieved through spontaneous parametric down-conversion in the system of nonlinear adiabatically coupled waveguides. We also demonstrate that the adiabatic couplers open the possibility to maintain the purity of generated Bell states in a relatively fabrication-fault-tolerant way. © 2014 Engineers Australia.

We develop a novel integrated scheme for on-chip generation of Bell states, which allows simultaneous spatial filtering of pump photons. It is achieved through spontaneous parametric down-conversion in a system of nonlinear adiabatically coupled waveguides. Importantly, the adiabatic couplers maintain the purity of generated Bell states in a relatively fabrication-fault-tolerant way. © 2014 IEEE.

We propose a novel integrated scheme for generation of Bell states, which allows simultaneous spatial filtering of pump photons. It is achieved through spontaneous parametric down-conversion in the system of nonlinear adiabatically coupled waveguides. We perform detailed analytic study of photon-pair generation in coupled waveguides and reveal the optimal conditions for the generation of each particular Bell state. Furthermore, we simulate the performance of the device under realistic assumptions and show that adiabatic coupling allows us to spatially filter the pump from modal-entangled photon pairs. Finally, we demonstrate that adiabatic couplers open the possibility of maintaining the purity of generated Bell states in a relatively fabrication-fault-tolerant way.

We demonstrate that generation and quantum walks of biphotons with non-classical spatial correlations in nonlinear waveguide arrays is tolerant to losses for different pump regimes, and suggest quick loss characterization approach based on nonlinear spectroscopy. © OSA 2013.

Entangled photon pairs, so-called biphotons, play a central role in the discussion of nonlocal quantum correlations. Moreover, they give rise to various applications such as quantum cryptography, teleportation and quantum computation. Particular versatile plattforms to investigate strong quantum correlations of entangled photons in a robust environment are optical waveguide arrays [1; 2]. However, in these settings the photons are generated outside the array which necessarily involves interfacing losses. © 2013 IEEE.

We realize experimentally quantum walks of photon-pairs generated in a quadratic nonlinear waveguide array, and demonstrate that the pump distance from the edge strongly affects the spatial correlations through the interference from virtual biphoton sources. © 2013 Optical Society of America.

We develop a systematic procedure for deriving the coupled-mode equations describing the spatial evolution of the slowly-varying amplitudes of electromagnetic modes in nonlinear periodic structures with loss and gain. Our approach is rigorously based on the Lorentz reciprocity theorem, and therefore it can be applied to a broad range of structures with metal and dielectric non-magnetic components, including plasmonic waveguides and metamaterials. We verify our approach through a direct comparison with the earlier analysis based on a direct perturbation theory for planar metal-dielectric structures, and furthermore demonstrate the application of our method to the three-dimentional multilayer fishnet metamaterials. © 2013 IEEE.

We propose a novel scheme for broadband generation of photon pairs combined with efficient spatial pump filtering. This is achieved through spontaneous parametric downconversion in a system of nonlinear adiabatically coupled waveguides. © 2013 Optical Society of America.

We suggest and demonstrate experimentally that evolution of classical light can simulate bi-photon generation through spontaneous parametric down-conversion and correlated quantum walks in waveguide arrays, including violation of Bell's inequality. © 2012 OSA.

We suggest and demonstrate experimentally that evolution of classicallight can simulate bi-photon generation through spontaneous parametric downconversion and correlated quantum walks in waveguide arrays, including violation of Bell's inequality. © 2011 Optical Society of America.

We suggest and demonstrate experimentally that evolution of classical light can simulate bi-photon generation through spontaneous parametric downconversion and correlated quantum walks in waveguide arrays, including violation of Bell's inequality. © 2011 Optical Society of America.

We suggest and demonstrate experimentally that evolution of classical light can simulate bi-photon generation through spontaneous parametric downconversion and correlated quantum walks in waveguide arrays, including violation of Bell's inequality. © 2011 Optical Society of America.

We suggest and demonstrate experimentally that evolution of classical light can simulate bi-photon generation through spontaneous parametric downconversion and correlated quantum walks in waveguide arrays, including violation of Bell's inequality. © 2012 OSA.

We suggest an application of pump-degenerate four-wave mixing process in tapered waveguides for generation of ultrashort pulses with central frequency tunable over the material transparency range. Our method can produce strongly compressed frequency-converted pulses in presence of group-velocity mismatch and group-velocity dispersion. Additionally, the proposed technique does not require pulse phase synchronization and effectively operates for strongly chirped pump pulses, thus enabling the use of longer nonlinear media for high conversion efficiency.

We demonstrate experimentally simultaneous photon-pair generation and quantum walks in a PPLN waveguide array where the output photon correlations can be controlled by varying the pump laser wavelength, switching from classical to quantum statistics. © OSA 2012.

We characterize experimentally the process of bi-photons generation through spontaneous parametric down-conversion in LiNbO 3 waveguide arrays. We demonstrate the formation of unique spatial-spectral distribution of photons and its dependence on phasematching conditions. © 2012 Optical Society of America.

We study experimentally the process of bi-photon generation through spontaneous parametric down-conversion in waveguide arrays. We show the formation of a unique spatial-spectral photon pattern and its dependence on the phase-matching conditions. © 2011 Optical Society of America.

We study experimentally the process of bi-photon generation through spontaneous parametric down-conversion in waveguide arrays. We show the formation of a unique spatial-spectral photon pattern and its dependence on the phase-matching conditions. © 2011 Optical Society of America.

We study experimentally the process of bi-photon generation through spontaneous parametric down-conversion in waveguide arrays. We show the formation of a unique spatial-spectral photon pattern and its dependence on the phase-matching conditions. © 2012 OSA.

We study experimentally the process of bi-photon generation through spontaneous parametric down-conversion in waveguide arrays. We show the formation of a unique spatial-spectral photon pattern and its dependence on the phase-matching conditions. © 2011 Optical Society of America.

We analyze the quantum statistics of photon pair generation through spontaneous four-wave mixing in nonlinear waveguide arrays and predict pump power-controlled transition between bunching and anti-bunching correlations due to self-focusing of the pump beam. © 2012 Optical Society of America.

We study photon-pair generation in arrays of cubic nonlinear waveguides through spontaneous four-wave mixing. We analyze numerically the quantum statistics of photon pairs at the array output as a function of waveguide dispersion and pump beam power. We show flexible spatial quantum state control such as pump-power-controlled transition between bunching and anti-bunching correlations due to nonlinear self-focusing.

We develop a systematic procedure for deriving the coupled-mode equations describing the spatial evolution of the slowly-varying amplitudes of electromagnetic modes in nonlinear periodic structures with loss and gain. Our approach is rigorously based on the Lorentz reciprocity theorem, and therefore it can be applied to a broad range of non-magnetic structures with metal and dielectric components, including plasmonic waveguides and metamaterials. We verify our approach through a direct comparison with the previous analysis based on a direct perturbation theory for planar metal-dielectric structures, and furthermore demonstrate the application of our method to the fishnet metamaterials. © 2012 American Institute of Physics.

We study experimentally and numerically the spatiotemporal evolution of short pulses in quadratic nonlinear waveguide arrays with coupled second-harmonic modes, revealing complex spectral transformations involving generation of new frequency components at the Brillouin zone edge. © 2011 Optical Society of America.

Lithium niobate waveguide arrays (WGAs) [1] offer rich possibilities for all-optical shaping, switching, and routing of short optical pulses. In such systems, light from the fundamental wave (FW) is coupled by the 2 nonlinearity to the second harmonic (SH) giving rise to a strong cascaded quadratic nonlinearity. Recently a new type of phase transition in the nonlinear localised states was identified due to the competition between self-focusing and SH waveguide coupling, where the SH phase profile abruptly switches from in-phase to staggered structure as the input power is increased [2]. However, the temporal extent of the short laser pulses used in realistic experiments leads to a complex pulse reshaping in the course of propagation. Never studied experimentally before, such temporal dynamics is important for utilising the phase transition phenomenon for applications in optical switching. In this work, we study the spatio-temporal dynamics of pulses in lithium niobate WGAs and describe numerically and characterize experimentally the complex spatio-temporal nonlinear pulse transformations associated with the phase transition. © 2011 IEEE.

We study experimentally and numerically the spatiotemporal evolution of short pulses in quadratic nonlinear waveguide arrays with coupled second-harmonic modes, revealing complex spectral transformations involving generation of new frequency components at the Brillouin zone edge. © 2011 AOS.

We study experimentally and numerically the spatiotemporal evolution of short pulses in quadratic nonlinear waveguide arrays with coupled second-harmonic modes, revealing complex spectral transformations involving generation of new frequency components at the Brillouin zone edge. © 2011 IEEE.

Nonlinear directional couplers (NLDC) allow for ultrafast all-optical switching. To date, various types of NLDCs have been studied, predominantly based on the Kerr [1] or cascaded quadratic nonlinearity [2] in second-harmonic generation (SHG). In the later case the switching can occur at lower powers because of a propagating-wave resonance effect. While a number of experiments to characterise the pulse propagation in Kerr-type couplers exist, till now the temporal behavior of short pulses in the NLDC with quadratic nonlinearity has never been studied experimentally. Several important questions such as the reason for incomplete switching and possible pulse compression factors remain unanswered. In this work we experimentally measure the pulse reshaping in a NLDC with second-order nonlinearity and show that pulse compression, break-up and back-switching play an important role in the switching process. © 2011 IEEE.

High-index-contrast nanowires offer unique advantages for manipulation of optical pulses in compact photonic circuits, providing high field confinement and enabling precise dispersion engineering [1]. Furthermore, arrays of coupled nanowire waveguides [2-4] open possibilities for efficient spatio-temporal shaping and switching of optical pulses. In order to harness these opportunities, it is essential to develop approaches to simultaneously control temporal and spatial dispersion, as these characteristics can be strongly connected in nanophotonic structures. In this work, we suggest that spatio-temporal dispersion can be tailored by introducing periodic waveguide bending, and demonstrate through numerical simulations the application of this concept to suppress pulse break-up. © 2011 IEEE.

We study photon pair generation through spontaneous parametric down conversion ac- companied by quantum walks in arrays of quadratic nonlinear waveguides and investigate various ways to control output photon correlations. © 2011 OSA.

Arrays of coupled optical waveguides provide a flexible platform for manipulation of optical beams and pulses [1]. Recently, the propagation of non-classical light in waveguide arrays has shown a surging attention. It was shown that quantum walks of correlated photon pairs realized through propagation in waveguide arrays can lead to nontrivial quantum correlations at the array output [2, 3] . However, all currently used schemes for quantum walks utilise correlated photon pairs generated externally to the array. Here, we propose and demonstrate numerically a novel scheme enabling simultaneous generation of correlated photon pair through spontaneous parametric downconversion (SPDC) and quantum walks inside a single photonic element - an array of quadratic nonlinear waveguides. This scheme avoids entirely the need for complex interfaces between the different photonic elements [3] and enables novel ways for control of the quantum correlations. © 2011 IEEE.

We study photon pair generation through spontaneous parametric down con- version accompanied by quantum walks in arrays of quadratic nonlinear waveguides and investigate various ways to control output photon correlations. © 2011 Optical Society of America.

We study photon pair generation through spontaneous parametric down conversion ac-companied by quantum walks in arrays of quadratic nonlinear waveguides and investigate various ways to control output photon correlations. © 2011 AOS.

We study photon pair generation through spontaneous parametric down conversion accompanied by quantum walks in arrays of quadratic nonlinear waveguides and investigate various ways to control output photon correlations. © 2011 IEEE.

We suggest an application of four-wave mixing process in tapered waveguides for generation of ultrashort pulses with tunable central frequency. Efficient conversion is demonstrated for strongly chirped pump pulses, which experience reduced nonlinear absorption. © 2010 IEEE.

We reveal simultaneous phase- and group-velocity matching for frequency doubling of ultra-short pulses at telecom wavelengths in LiNbO 3 membranes. Furthermore, we predict complete phase-matched cascaded third-harmonic generation for optimised membrane thickness. © 2009 Optical Society of America.

We reveal simultaneous phase-and group-velocity matching for frequency dou- bling of ultra-short pulses at telecom wavelengths in LiNbO3 membranes. Fur-thermore, we predict complete phase-matched cascaded third-harmonic gener-ation for optimised membrane thickness. © 2009 Optical Society of America.

We reveal simultaneous phase-and group-velocity matching for frequency dou-bling of ultra-short pulses at telecom wavelengths in LiNbO 3 membranes. Fur-thermore, we predict complete phase-matched cascaded third-harmonic gener-ation for optimized membrane thickness. © 2010 Optical Society of America.