Phase-sensitive parametric processes based on four-wave mixing (FWM) in third-order nonlinear media are attractive for the demonstration of numerous functionalities including low-noise amplification, high-sensitivity detection and signal phase quantization with applications to e.g. communication and sensing [1]. Until now, such processes have been demonstrated exclusively in single-mode optical fibers and waveguides. Meanwhile, the exploitation of the spatial (transverse) dimension of waveguides is also being explored for such applications, for instance in order to provide a new multiplexing degree of freedom in telecommunications [2]. One open question is whether the use of phase-sensitive processes can be made compatible with optical fibers and waveguides supporting multiple spatial modes. Some (inter-modal) phase-sensitive processes have been numerically investigated in few-mode fibers (FMFs) [3]. However, to the best of our knowledge, no experimental demonstration of phase-sensitive processes in FMFs has been reported so far. In this work, we demonstrate experimentally intra-modal phase-sensitive FWM, separately in two modes ( $\text{LP}_{01}$ and $\text{LP}_{11}$ ), in a 2-km long step-index FMF [4] supporting 4 LP-modes at 1550 nm.

Silicon modulators are used to generate frequency agile electro-optical frequency combs. Applications are discussed for both fine resolution dual comb spectroscopy and data communications based on wavelength division multiplexing transmission.

Optical frequency combs (OFCs) have played an important role over the past years for optical frequency metrology and synthesis, for astronomy, telecommunications, and spectroscopy. Among the different methods that have been studied for OFC generation, electro-optic frequency combs (EOFCs) using electro-optical modulators show a large flexibility in comb repetition rate, making it a solution of choice for absorption spectroscopy where a fine sampling in the frequency domain is usually required. Silicon photonics is a promising platform for EOFC generation, thanks to its high volume production and strong light confinement allowing to achieve small footprint photonic integrated circuits (PICs). Additionally, silicon PICs benefit from a direct compatibility with complementary metal-oxide semiconductor (CMOS) fabrication process. Carrier depletion-based modulators have already proved to be efficient and to achieve high bandwidth operation, which makes them suitable for EOFC generation. In this work we will show the first dual comb spectroscopy experiment using silicon optical modulators. As a proof of concept for spectroscopy applications, beating of two silicon EOFCs with slightly different repetition rates is observed in the RF domain using a multi-heterodyne detection technique. Each EOFC is generated from a silicon push-pull Mach-Zehnder modulator and shows typically 12 equally separated lines. The comb repetition rate is swept from 500 MHz to 12.5 GHz, thanks to the inherent flexibility of EOFCs, while their relative offset is kept steady (4 MHz). This technique is used to recover the transfer function of an optical band-pass filter without any tunable laser.

Optical frequency combs (OFCs) are involved in a large diversity of applications such as metrology, telecommunication or spectroscopy. Different techniques have been explored during the last years for their generation. Using an electrooptical modulator (EOM), it is possible to generate a fully tunable OFC for which the optical repetition rate is set by the frequency of the applied electrical radio frequency (RF) signal. In order to realize on-chip OFC generators, silicon photonics is a well-suited technology, benefiting from large scale fabrication facilities and the possibility to integrate the electronics with the EOM. However, observing OFCs with a repetition rate lower than 10 GHz can be challenging since such spacings are smaller than the typical resolution of grating-based optical spectrum analyzers. To overcome this issue, two alternative solutions based on heterodyne detection techniques are used to image the OFC on the electrical RF domain. The first technique consists in applying two frequencies close to each other simultaneously on the modulator, and observing the beating between the resulting two combs. Another method consists in observing the beating between the OFC and the input laser, once the frequency of this input laser has been shifted from the center of the OFC by means of an acousto-optic modulator. Based on both measurement techniques, OFCs containing more than 10 lines spaced with repetition rates from 100 MHz to 15 GHz have been observed. They are generated using a 4-mm long silicon depletionbased traveling-wave Mach-Zehnder modulator (MZM) operating at a wavelength of 1550 nm.

We report on the modeling and characterization of a truly single-mode hollow-core antiresonant fiber with a transmission band covering part of the near-infrared spectral region. Measured losses are 0.075 dB/m and 0.052 dB/m at 1.55 μm and 2.0 μm respectively.

Ghost imaging allows to image an object without directly seeing this object. Origi- nally demonstrated in the spatial domain using classical or entangled-photon sources, it was recently shown that ghost imaging can be transposed into the time domain to detect ultrafast signals with high temporal resolution. Here, using an incoherent supercontinuum light source whose spectral fluctuations are imaged using spectrum- to-time transformation in a dispersive fiber, we experimentally demonstrate magnified ghost imaging in the time domain. Our approach is scalable and allows to overcome the resolution limitation of time-domain ghost imaging.

We report on the first experimental demonstration of time-domain ghost imaging using a temporally incoherent classical light source. Our results open novel perspectives for dynamic imaging of ultrafast signals with high resolution even in the presence of noise.

Photon pair generation through four-wave mixing in photonic crystal fibers is highly sensitive to cladding pitch-induced fluctuation of the phase matching along the fiber. Our model describes its consequence on the pair spectrum.

Ghost imaging is a novel technique that produces the image of an object by correlating the intensity of two light beams, neither of which independently carries information about the shape of the object 1,2 . Ghost imaging has opened up new perspectives to obtain highly-resolved images 3 , even in the presence of noise and turbulence 4 . Here, exploiting duality between light propagation in space and time 5 , we demonstrate the temporal analogue of ghost imaging. We use a conventional fast detector that does not see the temporal ‘object’ to be characterised, and a slow integrating ‘bucket’ detector that does see the object but without resolving its temporal structure. Our experiments achieve temporal resolution at the picosecond level and are insensitive to temporal distortion that may occur after the object. The approach is scalable, can be integrated on-chip, and offers great promise for dynamic imaging of ultrafast waveforms.

Summary form only given. Optical fibre (either classical or microstructured) is a favourable medium for realization of sources of entangled photons for quantum communications. Indeed the photon pairs are generated through spontaneous Four Wave Mixing (FWM) directly in the fibre core and can thus be connected easily and without loss to the optical telecommunication network.We have realized such a source and characterized its performance. Our measurements showed a photon pair generation rate lower than expected in theory. Further characterization showed, as can be seen in Fig. 1A, a widened pair spectrum and a diminution of the generation rate compared to the prediction of our model (Fig. 1B) [2]. Such features can be explained by taking in account the intrinsic inhomogeneity of the fibre, i.e. the core and cladding dimensions fluctuation along the fibre. Indeed, a small variation of the fibre diameter implies a slightly different dispersion, hence shifted photon pair frequencies. To depict these uniformities, we extended our model through a similar approach as in Ref. [3], considering the fibre as an assembly of homogeneous sections, each one with its own length and phase mismatch. Consequently, the joint spectral intensity of pairs describing their generation probability for a given couple of frequencies is more complex. In Fig. 1B, we show the result of our numerical simulation for a purely uniform fibre with parameters corresponding to our source [1,2], and in the case of a linear variation of the zero dispersion wavelength along the fibre. In this specific case, a new analytical solution that will be presented, can be derived from our model, and is also shown in Fig. 1B as a comparison.

Ghost imaging is an optical technique that produces the image of an object by correlating the total amount of light transmitted through the object with the random intensity pattern that the object is irradiated with. When the technique is used with incoherent light sources, characterized by random temporal intensity fluctuations, it requires recording a very large number of distinct realizations to obtain a faithful image reproduction. In order to significantly reduce the number of realizations, one can use pre-programmed known patterns, so-called computational ghost imaging. Recently, ghost imaging was transposed into the time-domain to image ultrafast varying waveforms. Here, we report on a novel proof-of-concept experiment of computational ghost imaging in the time domain using wavelength multiplexing. By encoding different time-varying intensity patterns onto separate wavelength channels, we can perform simultaneous measurement of multiple realizations. This allows us to perform ghost imaging in real-time, without the need of probing the time-varying object repeatedly. Specifically, we use a programmable spectral filter to encode a set of 32 Hadamard-like time-varying intensity patterns onto a broadband LED light source. An electro-optic intensity modulator driven by an electrical waveform is used to create the time-varying object to be measured. The object is then reconstructed “blindly” by correlating the time-averaged transmission of each wavelength channels with the digitized form of the time-varying Hadamard patterns that illuminate the object. The temporal resolution of the measurement is currently to 0.5 s limited by the speed at which the variable spectral filter can be manipulated.

Scientists demonstrate the temporal analogue of ghost imaging with temporal resolution at the picosecond level. The approach is insensitive to temporal distortion that may occur after the object, and is scalable and can be integrated on-chip.

We report on the first demonstration of computational ghost imaging in the time domain using wavelength multiplexing. The wavelength-multiplexed Hadamard patterns used to probe a time-varying waveform enables precise image reconstruction in real time.

We present a new fibered architecture for generation of correlated photon pairs, in which the deleterious influence of Raman photons has been highly reduced by filling the core of a microstructured fiber with a liquid

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.

Using an incoherent supercontinuum, we demonstrate temporal ghost imaging with magnification without a time lens. This technique allows to image ultrafast signals with high resolution, even in the presence of severe distortion.