Abstract: Quantum photonics via quantum key distribution (QKD) offers a route to unconditional security but photon absorption, scattering, and losses have been an obstacle to implementing an untrusted-source QKD in optical fiber links in terms of distances and data rates. Whilst entangled photonic qudits offer enhanced information efficiency, noise robustness, and security level of QKD frequency and time entangled qudits promise resources to implement robust QKD in optical fibers. However, the spectral range occupied by frequency and time entangled qudits, their bandwidth, represents a significant issue towards their use for QKD applications in optical fiber networks. To implement high secret key rates for untrusted-source QKD in fiber links it is necessary to increase qudit dimensionality whilst keeping the time-bandwidth product as low as possible. However, this is a challenging task to achieve with current photonic platforms.

Abstract: A method for entropy scaling in quantum random number generators, comprising dividing one spatial mode into multiple spatial modes, delaying each spatial mode, and recombing the spatial modes; detecting first temporal states with synchronisation to a photon generation time and encoding the first temporal states into first time bins; detecting second temporal states in an arbitrary clock, and encoding the second temporal states into second time-bins.

Abstract: A photonic device which is configured to implement a recurrent neural network via reservoir computing is provided. The device includes a feed portion which mixes an input signal with previously generated and controllably attenuated portions of an output signal. The device further includes one or more propagating stages coupled to the feed portion. Each propagating stage propagates signals through a loop in both clockwise and counterclockwise directions, for example to be affected by nonlinear elements. The arrangement of the photonic device causes a nonlinear activation function to be realized by the propagating stages. The nonlinear activation function may be adjustable by adjusting various controllable elements in the device.

Abstract: A method and a system for single-shot multi-frame ultrafast terahertz imaging of a scene, the method comprising generating a pump beam and a probe beam: generating a THz beam from the pump beam and passing the THz beam through the scene: multiplexing the probe beam in the time domain and in the spatial-frequency domain. yielding a multiplexed probe beam; detecting a THz beam passing through the scene: guiding the multiplexed probe beam to a THz detection crystal and converting the multiplexed probe beam into mutually orthogonal linear polarized beams: guiding the mutually orthogonal linear polarized beams to a camera: and recovering frames of the scene from multiplexed images acquired by the camera.

Abstract: The disclosed structures and methods are directed to a chip for an optical gyroscope and methods of manufacturing of the chip for the optical gyroscope. The chip comprises a substrate, a waveguide having a first waveguide cladding layer and a waveguide core; and a ring resonator having a first ring cladding layer and a ring resonator core attached to the first ring cladding layer. A side wall of the ring resonator core forms an obtuse angle with an upper surface of the substrate. The method comprises depositing a first cladding layer on an upper surface of a silicon substrate; depositing a core layer; depositing a resist mask pattern to define a form of a ring resonator core and a form of a waveguide core; etching the core layer outside of the resist mask pattern; and stripping the resist mask pattern off.

Abstract: An optical information processing system comprising a nonlinear element selected in relation to input optical pulses to initiate nonlinear optical frequency conversion and a detection unit, the nonlinear element receiving encoded information input in form of pulsed light, pulsed light from the nonlinear element being read-out by the detection unit for spectro-temporal feature extraction, and the readout being used to train the system on a specific target to obtain a task-specific output or re-directed to the nonlinear element to obtain an input-dependent output, yielding processed information comprising selective positions in an output of the system. A method for training an optical system comprises, for each individual optical input information, reading specific optical amplitude or phase features from specific output bins of the system in time or frequency, weighting and evaluating the specific features towards optimizing user-defined fitness function to identify, classify, or fit the input information.

Abstract: A method and a system for controlling an output of an optical system, the method comprising generating a plurality of optical signal components having different optical properties and passing the generated optical signal components as input to an optical system comprising an optical device and/or an optical medium; an output of the optical system being based on interactions of the signal components within the optical device and/or the optical medium; and relative proportions of the optical signal components that are generated and individual optical properties thereof being selected to control the output of the optical system.

Abstract: A THz waveguide is described, comprising four conductive wires separated by an air gap, the THz waveguide allowing low-loss and dispersion-free propagation of a THz signal. The system for terahertz polarization-division multiplexing comprises at least two THz sources, a THz waveguide and a THz receiver, wherein said THz waveguide comprises four conductive wires separated by an air gap; THz pulses from the THz sources being coupled into the THz waveguide; the THz waveguide transmitting the THz pulses independently, the THz waveguide operating as a broadband polarization-division multiplexer. The method for terahertz polarization-division multiplexing, comprising multiplexing THz pulses from terahertz sources in free-space, coupling resulting multiplexed THz pulses into a THz waveguide comprising four conductive wires separated by an air gap; and demultiplexing the multiplexed THz pulses after propagation in the waveguide.

Abstract: A method and a system for generating a hyper-entangled high-dimensional time-bin frequency-bin state, the method comprising generating a hyper-entangled state composed of a time-bin and frequency-bin encoded state, and individually modifying at least one of: i) the amplitude and ii) the phase of the state components at different frequency-bins and different time-bins of the hyper-entangled state. The system comprises a non-linear medium exited with multiple pulses in broad phase-matching conditions, a frequency mode separator and an amplitude/phase modulator, the frequency mode separator temporally and spatially separating frequency modes of the hyper-entangled state, the amplitude/phase modulator individually modifying at least one of: i) the amplitude (and ii) the phase of the state components at different frequency-bins and different time-bins of the hyper-entangled state.

Abstract: A system and a method for phase extraction of a multi-path interferometer, the method comprising generating a reference signal of a coherence length longer than an arm length difference of the multi-path interferometer; splitting the reference signal into a frequency shifted reference signal and an unshifted reference signal; recombining the frequency shifted reference signal and the unshifted reference signal into a polarization- and frequency-multiplexed reference signal, and feeding the polarization- and frequency-multiplexed reference signal to the multi-path interferometer; detecting frequency shifted and unshifted output signals of the multi-path interferometer; and determining the interferometer phase from the detected signal.

Abstract: A method and a system for arbitrary optical waveform generation from an optical input, the system comprising an optical shaper comprising unbalanced interferometers with at least one delay, the delay being selected of at least 0.1 ps, an optical sampling readout selected for measuring optical waveforms of at least 0.

Abstract: A device, a system and a method for homodyne solid-state biased coherent detection of terahertz pulses in a range between 0.1 and 11 THz, the device comprising a metallic slit between, and parallel to, two longitudinal metallic electrodes, deposited on a surface of a substrate, and covered with a layer of nonlinear material, wherein a width of the metallic slit and a thickness of the nonlinear material layer are selected in relation to a central wavelength of the THz pulses. The method comprises focusing a THz beam and a pulsed laser beam of pulse energies in a range between 10 and 100 nJ onto the metallic slit, the metallic electrodes being biased by a static DC voltage bias selected in a range between 20 VPP and 200 VPP; and retrieving a terahertz pulse waveform using the terahertz pulse repetition rate as synchronism.

Abstract: A waveguide for time-domain integration of THz pulses, comprising two wires extending from an input gap gin to an output gap gout at a tapering angle ? relative to a longitudinal axis, a gap of the waveguide decreasing linearly from the input gap gin to the output gap gout, wherein a size of the output gap is at least one order of magnitude smaller than a central wavelength ?THz in a spectrum of the THz pulses, and a method for time-domain integration of THz pulses, comprising confining input THz pulses in the waveguide.

Abstract: The disclosed structures and methods are directed to a chip for an optical gyroscope and methods of manufacturing of the chip for the optical gyroscope. The chip comprises a substrate, a waveguide having a first waveguide cladding layer and a waveguide core; and a ring resonator having a first ring cladding layer and a ring resonator core attached to the first ring cladding layer. A side wall of the ring resonator core forms an obtuse angle with an upper surface of the substrate. The method comprises depositing a first cladding layer on an upper surface of a silicon substrate; depositing a core layer; depositing a resist mask pattern to define a form of a ring resonator core and a form of a waveguide core; etching the core layer outside of the resist mask pattern; and stripping the resist mask pattern off.

Abstract: A THz waveguide is described, comprising four conductive wires separated by an air gap, the THz waveguide allowing low-loss and dispersion-free propagation of a THz signal. The system for terahertz polarization-division multiplexing comprises at least two THz sources, a THz waveguide and a THz receiver, wherein said THz waveguide comprises four conductive wires separated by an air gap; THz pulses from the THz sources being coupled into the THz waveguide; the THz waveguide transmitting the THz pulses independently, the THz waveguide operating as a broadband polarization-division multiplexer. The method for terahertz polarization-division multiplexing, comprising multiplexing THz pulses from terahertz sources in free-space, coupling resulting multiplexed THz pulses into a THz waveguide comprising four conductive wires separated by an air gap; and demultiplexing the multiplexed THz pulses after propagation in the waveguide.

Abstract: A method for entropy scaling in quantum random number generators, comprising dividing one spatial mode into multiple spatial modes, delaying each spatial mode, and recombing the spatial modes; detecting first temporal states with synchronisation to a photon generation time and encoding the first temporal states into first time bins; detecting second temporal states in an arbitrary clock, and encoding the second temporal states into second time-bins.

Abstract: A system for designing a photonics system, comprising a topology optimization module and a component parameter optimization module; wherein the topology optimization module searches candidate photonics systems through photonics combinations of component; and the component parameter optimization module searches for component parameters of the candidate photonics systems to simulate successive candidate photonics systems in a desired degree-of-freedom according to a target characteristic of the photonics system. The method comprises searching through different photonics combinations of components and component parameters and selecting candidate photonics systems, and searching component parameters of the candidate photonics systems in a desired degree-of-freedom according to a target characteristic of the photonics system.

Abstract: A method and a system for generating a hyper-entangled high-dimensional time-bin frequency-bin state, the method comprising generating a hyper-entangled state composed of a time-bin and frequency-bin encoded state, and individually modifying at least one of: i) the amplitude and ii) the phase of the state components at different frequency-bins and different time-bins of the hyper-entangled state. The system comprises a non-linear medium exited with multiple pulses in broad phase-matching conditions, a frequency mode separator and an amplitude/phase modulator, the frequency mode separator temporally and spatially separating frequency modes of the hyper-entangled state, the amplitude/phase modulator individually modifying at least one of: i) the amplitude (and ii) the phase of the state components at different frequency-bins and different time-bins of the hyper-entangled state.

Abstract: A device, a system and a method for homodyne solid-state biased coherent detection of terahertz pulses in a range between 0.1 and 11 THz, the device comprising a metallic slit between, and parallel to, two longitudinal metallic electrodes, deposited on a surface of a substrate, and covered with a layer of nonlinear material, wherein a width of the metallic slit and a thickness of the nonlinear material layer are selected in relation to a central wavelength of the THz pulses. The method comprises focusing a THz beam and a pulsed laser beam of pulse energies in a range between 10 and 100 nJ onto the metallic slit, the metallic electrodes being biased by a static DC voltage bias selected in a range between 20 VPP and 200 VPP; and retrieving a terahertz pulse waveform using the terahertz pulse repetition rate as synchronism.

Abstract: A system and a method for phase extraction of a multi-path interferometer, the method comprising generating a reference signal of a coherence length longer than an arm length difference of the multi-path interferometer; splitting the reference signal into a frequency shifted reference signal and an unshifted reference signal; recombining the frequency shifted reference signal and the unshifted reference signal into a polarization- and frequency-multiplexed reference signal, and feeding the polarization- and frequency-multiplexed reference signal to the multi-path interferometer; detecting frequency shifted and unshifted output signals of the multi-path interferometer; and determining the interferometer phase from the detected signal.