Experimental phase-space-based optical amplification of scar modes

Waves billiard which are chaotic in the geometrical limit are known to support non-generic spatially localized modes called scar modes. The interaction of the scar modes with gain has been recently investigated in optics in micro-cavity lasers and vertically-cavity surface-emitting lasers. Exploiting the localization properties of scar modes in their wave analogous phase space representation, we report experimental results of scar modes selection by gain in a doped D-shaped optical fiber

Analysis of High-Index Contrast Lithium Niobate Waveguides Fabricated by High Vacuum Proton Exchange

International audience—High-index contrast waveguides fabricated with precise control and reproducibility are of high interest for nonlinear and/or electro-optical highly efficient and compact devices for quantum and classical optical data processing. Here we present a new process to fabricate planar and channel optical waveguides on lithium niobate substrates that we called High Vacuum Proton Exchange (HiVacPE). The main purpose was to improve the reproducibility and the quality of the produced waveguides by limiting and controlling the water traces in the melt, which is used for the ionic exchange. Moreover, we discovered that, when the acidity of the bath is increased, depending on substrate orientation (Z-cut or X-cut) the waveguides are completely different in term of crystallographic properties, index profiles and nonlinearity. The best-obtained channel waveguides exhibit a refractive index contrast as high as 0.04 without any degradation of the crystal nonlinearity and state of the art propagation losses (0.16dB/cm). We have also demonstrated that the HiVacPE process allows fabricating waveguides on Z-cut substrate with high-index contrast up to 0.11 without degrading the crystal nonlinearity but high strain induced propagation losses. On top of that, we proposed an original and very useful method of analyzing waveguides with complex index profiles. This method can be used for the analysis of any waveguides whose core contains several layers

Niobate de lithium périodiquement polarisé à courte période et perspectives d'application

International audienceLe niobate de lithium périodiquement polarisé (PPLN) sur des périodes courantes de 6 à 22 µm trouve actuellement de nombreuses applications en optique non linéaire (ONL). La micro-structuration à plus courte période, c'est-à-dire de 2,5 µm à 300 nm, permettrait de nouvelles fonctionnalités, non seulement en ONL mais aussi en électro-optique. Les problèmes technologiques posés par ce défi sont présentés, ainsi que quelques exemples d'applications

Broadband integrated beam splitter using spatial adiabatic passage

Light routing and manipulation are important aspects of integrated optics. They essentially rely on beam splitters which are at the heart of interferometric setups and active routing. The most common implementations of beam splitters suffer either from strong dispersive response (directional couplers) or tight fabrication tolerances (multimode interference couplers). In this paper we fabricate a robust and simple broadband integrated beam splitter based on lithium niobate with a splitting ratio achromatic over more than 130 nm. Our architecture is based on spatial adiabatic passage, a technique originally used to transfer entirely an optical beam from a waveguide to another one that has been shown to be remarkably robust against fabrication imperfections and wavelength dispersion. Our device shows a splitting ratio of 0.52$\pm$0.03 and 0.48$\pm$0.03 from 1500\,nm up to 1630\,nm. Furthermore, we show that suitable design enables the splitting in output beams with relative phase 0 or $\pi$. Thanks to their independence to material dispersion, these devices represent simple, elementary components to create achromatic and versatile photonic circuits

Up-conversion detectors at 1550 nm for quantum communication: review and recent advances

International audienceUp-conversion, or hybrid, detectors have been investigated in quantum communication experiments to replace Indium-Gallium-Arsenide avalanche photodiodes (InGaAs-APD) for the detection of infrared and telecom single photons. Those detectors are based on the supposedly noise-free process of frequency up-conversion, also called sum-frequency generation (SFG), using a second order ($\chi^2$) non-linear crystal. Powered by an intense pump laser, this process permits transposing with a certain probability the single photons at telecom wavelengths to the visible range where silicon APDs (Si-APD) operate with a much better performance than InGaAs detectors. To date, the literature reports up-conversion detectors having efficiency and noise figures comparable to that of the best commercially available IngaAs-APDs. However, in all of these previous realizations, a pump-induced noise is always observed which was initially expected to be as low as the dark count level of the Si-APDs. Although this additional noise represents a problem for the detection, up-conversion detectors have advantageously replaced InGaAs-APDs in various long-distance quantum cryptography schemes since they offer a continuous regime operation mode instead of a gated mode necessary for InGaAs-APDs, and the possibility of much higher counting rates. Despite attempted explanations, no detailed nor conclusive study of this noise has been reported.
The aim of this paper is to offer a definitive explanation for this noise. We first give a review of the state of the art by describing already demonstrated up-conversion detectors. We discuss these realizations especially regarding the choices made for the material, in bulk or guided configurations, the single photon wavelengths, and the pump scheme. Then we describe an original device made of waveguides integrated on periodically poled lithium niobate (PPLN)or on single-domain lithium niobate aimed at investigating the origin of the additional pump-induced noise. The poled waveguides are designed to up-convert single photons at 1550 nm to 600 nm when a 980 nm diode laser is used as pump. We obtain an overall efficiency of about 0.6% for a noise level of about $8\times 10^3$ counts/s. This overall efficiency includes both insertion and propagation losses, and internal up-conversion and quantum detection (Si-APD) efficiencies. Despite a low efficiency value compared to what has been obtained so far by other groups, the efficiency/noise ratio is still comparable which still allows us investigating the noise issue. 
From the spectrum obtained in both poled and non-poled waveguides we conclude that the noise comes from an alternative phase-matching scheme which permits creating paired photons at 1550 and 2700 nm wavelength by down-conversion of the 980 nm pump laser. Knowing that 1550 nm corresponds to the input signal wavelength, up-conversion of actual signal or pump-induced photons at this particular wavelength cannot be discriminated, therefore contributing to the noise at the final wavelength of 600 nm. We believe that this process of down-conversion of the pump laser to the signal wavelength (plus complementary wavelength) is responsible for the unexpected noise level reported in all the up-conversion detector realizations

Étude en champ proche optique de guides optiques, de luminescence et d'effets photoréfractifs dans des cristaux

Ce manuscrit porte sur l'étude de phénomènes photoréfractifs et de luminescence dans des guides d'ondes optiques plans et canaux, en utilisant la technique SNOM. Des structures guidantes créées dans du LiNbO/3, LiTaO/3, SBN et LiF par plusieurs méthodes, ont été caractérisées par l'acquisition simultanée d'une image topographique et d'une image optique de champ proche. Pour la première fois des effets électro-optiques sous champ électrique externe permettant la création de solitons spatiaux photoréfractifs a été étudiée dans des guides monocristallins de SBN, dans une configuration SNOM. Nous présentons également les premiers guides canaux obtenus par implantation ionique dans le SBN, ainsi que les études d'effets photoréfractifs sous champ dans ces guides. Par ailleurs, une étude spectroscopique locale a été réalisée sur des structures de centres colorés dans du LiF et le guidage optique dans des structures en ruban de centres colorés a été également examiné en configuration SNOMLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Spontaneous Polarization Reversal Induced by Proton Exchange in Z-Cut Lithium Niobate α-Phase Channel Waveguides

The α-phase waveguides directly produced in one fabrication step only are well known for preserving both the excellent nonlinear properties and the ferroelectric domains orientation of lithium niobate substrates. However, by using the piezoresponse force microscopy (PFM), we present a coherent study on ferroelectric dipoles switching induced by the fabrication process of α-phase waveguides on Z-cut congruent lithium niobate (CLN) substrates. The obtained results show that the proton exchange process induces a spontaneous polarization reversal and a reduction in the piezoelectric coefficient d33. The quantitative assessments of the impact of proton exchange on the piezoelectric coefficient d33 have been quantified for different fabrication parameters. By coupling systematic PFM investigation and optical characterizations of α-phase protonated regions and virgin CLN on ±Z surfaces of the samples, we find a very good agreement between index contrast (optical investigation) and d33 reduction (PFM investigations). We clearly show that the increase in the in-diffused proton concentration (increase in index contrast) in protonated zones decreases the piezoelectric coefficient d33 values. Furthermore, having a high interest in nonlinear performances of photonics devices based on PPLN substrates, we have also investigated how deep the spontaneous polarization reversal induced by proton exchange takes place inside the α-phase channel waveguides

The evanescent waves in metallic strip gratings and complex structures in subwavelength regime

The paper investigates the formation of evanescent waves in metallic strip gratings on the Ag/ZnO/SiO2/Si structure with silver strips when TEz incident wave in the radiofrequency range was used. The Ag/ZnO/SiO2/Si structure was fabricated by vacuum thermal evaporation technique and Scanning Electron Microscopy was used to evidence its high quality structure with parallel silver strips of same width and thickness. Simulation of the evanescent wave formation at the edge of Ag strips, with thicknesses in the range of micrometers, was performed, before performing the test in the subwavelength regime by the mean of a new transducer improved with metamaterials lens. The generation in slits, in air, of the electric evanescent mode, when metallic strip grating was excited with a TEz polarized wave at a frequency of 474 MHz, was successfully demonstrated

Contrôle des modes par le chaos des rayons dans des fibres optiques hautement multimodes

National audienceDes systèmes simples, linéaires et conservatifs peuvent exhiber des dynamiques complexes du fait de leur géométrie. Le propos du chaos ondulatoire est d'étudier l'implication de ces dynamiques complexes sur le comportement des ondes[1]. Les fibres optiques hautement multimodes (les " f.o.h.m ") se révélent ainsi être de précieux supports expérimentaux de visualisation, d'étude et d'exploitation des manifestations ondulatoires des dynamiques complexes de systèmes hamiltoniens. En effet, les f.o.h.m constituent des analogues ondulatoires des billards, paradigmes des systèmes dynamiques classiques a faibles degrés de liberté. En effet, dans la limite géométrique des rayons, la propagation d'un rayon optique le long d'une fibre optique est formellement équivalente à l'évolution temporelle d'un rayon dans un système borné a deux dimensions. Ces billards optiques constituent des supports très flexibles notamment pour étudier des dynamiques de différentes natures : en tronquant la section transverse d'une f.o.h.m. on peut explorer les régimes de dynamique régulìère, chaotique voire mixte. De plus, gain et effets non linéaire de type Kerr aisément exploitables dans les fibres optiques, permettent d'associer les effets de la dynamique classique à une réponse active du milieu. Fort de nos travaux menés sur l'analyse des propriétés spatiales des modes de propagation dans des billards optiques chaotiques et mixtes, nous montrerons lors de cet exposé comment les propriétés de la dynamique des rayons géométriques permettent de contrôler les modes dans des fibres hautement multimodes[2]