We demonstrate theoretically and experimentally a high level of control of the four-wave mixing process in an inert gas-filled inhibited-coupling guiding hollow-core photonic crystal fiber. The specific multiple-branch dispersion profile in such fibers allows both correlated and separable bi-photon states to be produced. By controlling the choice of gas and its pressure and the fiber length, we experimentally generate various joint spectral intensity profiles in a stimulated regime that is transferable to the spontaneous regime. The generated profiles may cover both spectrally separable and correlated bi-photon states and feature frequency tuning over tens of THz, demonstrating a large dynamic control that will be very useful when implemented in the spontaneous regime as a photon pair source.

Photon-pair states, whether spectrally correlated or separable, can all be very useful in quantum technology applications. For example, the former are used for improving the security of quantum key distribution, whilst the latter are the backbone in heralded single photon sources. It has been shown that the amount of spectral correlations is well-described by the shape of the Joint Spectral Amplitude function (JSA), which mostly depends on the relative group velocity relation between the pump, signal and idler photons within the source medium [1].

We experimentally show how multiband dispersion properties of inhibitedcoupling hollow-core fibers allow to control the spectral correlations of photon pairs generated through four-wave-mixing in a fiber filled with non-linear gas.

We report on the experimental characterization of a novel nonlinear liquid-filled hollow-core photonic crystal fiber for the generation of photon pairs at a telecommunication wavelength through spontaneous four-wave mixing (SFWM). We show that the optimization procedure in view of this application links the choice of the nonlinear liquid to the design parameters of the fiber, and we give an example of such an optimization at telecom wavelengths. Combining the modeling of the fiber and classical characterization techniques at these wavelengths, we identify for the chosen fiber and liquid combination SFWM phase-matching frequency ranges with no Raman scattering noise contamination. This is a first step toward obtaining a telecom band fibered photon-pair source with a high signal-to-noise ratio.

Fibered sources of photon pairs can be easily integrated into future quantum communication networks. However, in silica-core fibres, the broadband spectrum of spontaneous Raman scattering strongly contributes to uncorrelated noise photons degrading the quality of the source. To overcome the problem of the silica Raman scattering, a new architecture was recently proposed, with hollow-core photonic crystal fibers (LF-HCPF) whose core and cladding are filled with a non-linear liquid. As opposed to the Raman scattering spectrum of silica, which is broadband and continuous, the Raman scattering spectrum of liquids is composed of narrow lines. Thus, generating photon pairs between these narrow lines permits to avoid the spectral overlap between the SFWM pairs and the Raman photons. A near infra-red LF-HCPCF photon pair source has been demonstrated, featuring a three order of magnitude suppression of the Raman noise [1]. We have also demonstrated the first non-linear LF-PCF with a transmission band and a zero-dispersion-wavelength (ZDW) in the telecom wavelength range combined with a non-linearity of the same order of magnitude as the one of silica, as a first step towards a Raman-free photon pair source in the telecom band [2]. Injecting light on both sides of this fiber in a Sagnac loop configuration can then be used to obtain entanglement.

We experimentally demonstrate, for the first time to our knowledge, the generation of correlated photon pairs in a liquid-core photonic crystal fiber. Moreover, we show that, thanks to the specific Raman properties of liquids, the Raman noise (which is the main limitation of the performance of silica-core fiber-based correlated photon pair sources) is highly reduced. With a demonstrated coincident-to-accidental ratio equal to 63 and a pair generation efficiency of about 10$^{-4}$ per pump pulse, this work opens the way for the development of high quality correlated photon pair sources for quantum communications.

We present a study on the transient operation of a microcavity under a coherent excitation. Through appropriate shaping of the incident signal, the coupling efficiency and the enhancement of the non-linearities are shown to be increased.

We experimentally demonstrate the generation of correlated photon pairs in a liquid-core fibre. Thanks to the specific Raman properties of liquids, this original architecture will provide high quantum quality photon pair sources for quantum telecommunications.

Coherent excitation of a nonlinear semiconductor microcavity is theoretically reported. It intends to counterbalance the frequency drift of the cavity resonance driven by the nonlinear refractive effects, which causes a limitation in the energy coupling efficiency of an input pulse into the cavity resonance. We show that exciting such a nonlinear microcavity with tailored chirped pulses allows to maintain the benefit of light localization and to further enhance light-matter interactions, opening the way to the realization of highly efficient nonlinear devices.

Correlations of twin beams generated by parametric down-conversion are quantitatively determined by two-photon counting interferometery. Compared with incoherent light, photon extrabunching at the fs scale is unambiguously and precisely measured.

Exciting work is being done in quantum information theory and the detection of low light levels.

For many years twin beams originating from parametric down-converted light beams have aroused great interest and attention in the photonics community. One particular aspect of the twin beams is their peculiar intensity correlation functions, which are related to the coincidence rate of photon pairs. Here we take advantage of the huge bandwidth offered by two-photon absorption in a semiconductor to quantitatively determine correlation functions of twin beams generated by spontaneous parametric down-conversion. Compared with classical incoherent sources, photon extrabunching is unambiguously and precisely measured, originating from exact coincidence between down-converted pairs of photons, travelling in unison. These results strongly establish that two-photon counting in semiconductors is a powerful tool for the absolute measurement of light beam photon correlations at ultrashort timescales.

We study the photon correlation properties of broadband parametric down-converted light. The measurement of the photon correlation is carried out thanks to a modified Hanbury Brown-Twiss interferometer based on two photon absorption in GaAs detector. Since this method is not affected by the phase matching conditions of the detecting apparatus (so called "final state post-selection"), the detection bandwidth can be extremely large. This is illustrated by studying, with the same apparatus, the degree of second order coherence of parametric light in both degenerate and non-degenerate cases. We show that our experiment is able to determine the coherent as well as the incoherent contributions to the degree of second order coherence of parametric light with a time resolution in the fs range scale.

In recent years, a significant amount of attention has been drawn towards all-optical semiconductor switching. To that respect, exploitation of light localization, in slow light photonic crystal waveguides (PCWs) or in microcavities, is of considerable interest because it enables enhancement of optical nonlinearities. Recently, we observed experimental and theoretical enhancement of optical Kerr effect, two-photon absorption (TPA) and free-carrier index changes (FCI) in GaAs PCWs, which demonstrated the important role of group velocity. This paper presents an original approach to map and design light localizing semiconductor structures for optical switching applications. In any nonlinear process, each nonlinear coefficient of the bulk material must be enhanced by a power of the local field factor f, which is simply related to the square root of the slow down factor for PCWs, or of the Q-factor for microcavities. So, a p-th order nonlinear susceptibility of the bulk material should be multiplied by fp+1 in the nonlinear propagation equation. The desired nonlinearity for switching applications is the Kerr effect through which a relative nonlinear phase-shift of pi must be achieved. However, semiconductor materials present n-photon absorption (n-PA). n-PA transfers power from light to free- carriers that produce FCI, which adds an additional phase-shift to the optical beam and thus competes with the Kerr effect, though some argue that FCI switching can be used when carrier lifetime is short.

We propose an original adaptive wavefront holographic setup based on the photorefractive effect (PR), to make real-time measurements of acousto-optic signals in thick scattering media, with a high flux collection at high rates for breast tumor detection. We describe here our present state of the art and understanding on the problem of breast imaging with PR detection of the acousto-optic signal.

We present a theoretical study and an experimental demonstration of stimulated Raman effect in a hollow core photonic crystal fiber filled with a low index nonlinear liquid (ethanol).

We present the operating principle and a first experimental characterization of a holographic rangefinder, that couples a two wave mixing phase demodulation set-up with a frequency modulated laser source. In its first implementation, the system allows millimetre sensitivity on tens of meters measurement range with the ability to work with scattering surfaces.

We realized an efficient single spatial mode Raman generator that uses an ethanol filled HC-PCF. Despite the non optimized nature of the commercial fiber used, good performances have been obtained and the technique presents interesting opportunities for the realization of Raman amplifiers and generators able to operate in the CW regime using optimized fibers.

Acousto-optic imaging combined with adaptive wavefront interferometry is used to reveal local optical properties of objects embedded within thick scattering media. We will present experimental configurations in connection with the requirements needed for in-vivo imaging.

Photonic crystals show several properties that present great interest for the implementation of nonlinear optical functions. We will show how light localization in these structures will largely increase the efficiency of the nonlinear mechanism.