Laser Optical Feedback Imaging (LOFI) controlled by an electronic feedback loop.

International audienceIn autodyne interferometry, the beating between the reference beam and the signal beam takes place inside the laser cavity and therefore the laser fulfills simultaneously the roles of emitter and detector of photons. In these conditions, the laser relaxation oscillations play a leading role, both in the laser quantum noise which determines the signal to noise ratio (SNR) and also in the laser dynamics which determines the response time of the interferometer. In the present study, we have experimentally analyzed the SNR and the response time of a Laser Optical Feedback Imaging (LOFI) interferometer based on a Nd3+ microchip laser, with a relaxation frequency in the megahertz range. More precisely, we have compared the image quality obtained, when the laser dynamics is free and when it is controlled by a stabilizing electronic feedback loop using a differentiator. From this study, we can conclude that when the laser time response is shorter (i.e. the LOFI gain is lower), the image quality can be better (i.e. the LOFI SNR can be higher) and that the use of an adapted electronic feedback loop allows high speed LOFI with a shot-noise limited sensitivity. Despite the critical stability of the electronic feedback loop, the obtained experimental results are in good agreement with the theoretical predictions

Génération de seconde harmonique dans les microdisques de phosphure de gallium intégrés sur silicium

The goal of this thesis is to determine the best conditions to manage the second harmonic generation (SHG) from afundamental in the telecom C-band (around 1.55 (Jm) in gallium phosphide microdisks integrated on silicon. Findingtechnical solutions to take advantage of the non linear effects in these devices is a contribution to the actual efforts madeto develop integrated photonics circuits.In this work, the approximate resolution of the electromagnetic wave propagation equation completed by a nonlinearsource led to two "charts" indicating, for one, the necessary conditions for SHG, and for the other, the conversionefficiency theoretically allowed according to the chosen parameters. Thanks to the Foton laboratory expertise inmonolithical integration of GaP on Si, the influence on the SHG of specific structural defects was studied. This has led tothe proposal of two new phase matching techniques in GaP/Si microdisks.From an experimental point of view, this work led to the fabrication of two setups, the fi rst one, to make tapered opticalfibres and dimpled tapers, the second one, to make optical characterizations of microdisks and to study SHG in these systems.Cette thèse a pour but de déterminer les meilleures conditions possibles pour réaliser une génération de seconde harmonique (SHG) à partir d'un fondamental dans la bande C télécom (autour de 1.55 JJm) dans des microdisques de phosphure de gallium intégrés sur silicium. Il s'inscrit dans les efforts actuels de développement de circuits photoniques intégrés en étudiant une proposition technique pour tirer parti des effets non linéaires en optique. A partir d'une résolution approchée de l'équation de propagation des ondes électromagnétiques comportant un terme source d'origine non linéaire, il a permis d'aboutir à deux "cartes" indiquant, pour l'une, les conditions nécessaires à la SHG, pour l'autre, l'efficacité théorique attendue suivant les paramètres retenus. S'appuyant sur l'expertise du laboratoire Folon en matière d'intégration monolithique de GaP sur Si, une étude de l'influence sur la SHG de certains défauts de cristallisation a été menée et a conduit à la proposition de deux nouvelles techniques d'accord de phase dans les disques de GaP épitaxiés sur Si. D'un point de vue expérimental, ce travail de thèse a permis, d'une part, de doter le laboratoire d'un banc de fabrication de fibres effilées (tapers) et fibres effilées gaufrées (dimpled tapers) et, d'autre part, d'un banc de caractérisation optique des microdisques adapté à l'étude de la SHG

Micro-résonateurs à modes de galerie pour l’optique non-linéaire et les applications Lasers

National audienceNous détaillerons quelques configurations de micro-résonateurs à modes de galerie illustrant le fait que leurs propriétés intrinsèques peuvent être exploitées pour la miniaturisation de sources optiques de grande qualité ou de fonctions d’optique non-linéaire

Robust Geometries for Second-Harmonic-Generation in Microrings Exhibiting a 4-Bar Symmetry

Microring resonators made of materials with a zinc-blend or diamond lattice allow exploiting their 4-bar symmetry to achieve quasi-phase matching condition for second-order optical nonlinearities. However, fabrication tolerances impose severe limits on the quasi-phase matching condition, which in turn degrades the generation efficiency. Here, we present a method to mitigate these limitations. As an example, we studied the geometry and the pump wavelength conditions to induce the second-harmonic generation in silicon-based microrings with a second-order susceptibility chi(2)=/0. We found the best compromises between performances and experimental requirements, and we unveil a strategy to minimize the impacts of fabrication defects. The method can be easily transferred to other material systems

Investigation des propriétés optiques des microdisques de phosphure de gallium

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Cathodoluminescence hyperspectral analysis of whispering gallery modes in active semiconductor wedge resonators

International audienceWhispering gallery mode resonators are key devices for integrated photonics. Despite their generalization in fundamental and applied science, information on spatial confinement of light in these structures is mostly retrieved from purely spectral analysis. In this work, we present a detailed spectral and spatial characterization of whispering gallery modes in active semiconductor microdisk resonators by use of hyperspectral cathodoluminescence. By comparing our experimental findings to finite element simulations, we demonstrate that the combination of spectral and spatial measurements enables unique identification of the modes and even reveals specific features of the microresonator geometry, such as a wedge profile

Second harmonic generation in gallium phosphide microdisks on silicon: from strict 4ˉ\bar{4} to random quasi-phase matching

International audienceThe convergence of nonlinear optical devices and silicon photonics is a key milestone for the practical development of photonic integrated circuits. The associated technological issues often stem from material incompatibility. This is the case of second order nonlinear processes in monolithically integrated III-V semiconductor devices on silicon, where structural defects called antiphase domains strongly impact the optical properties of the material. We theoretically investigate the influence of antiphase domains on second harmonic generation in III-V whispering gallery mode microresonators on silicon and focus on the effects of the antiphase domains’ mean size (i.e. the correlation length of the distribution). We demonstrate that the domain distributions can have opposite effects depending on the nonlinear process under consideration: while antiphase domains negatively impact second harmonic generation under ¯4 quasi-phase matching conditions (independent of the correlation length), large conversion efficiencies can arise far from ¯4-quasi-phase matching provided that the APD correlation length remains within an appropriate range, and is still compatible with the spontaneous emergence of such defects in the usual III-V on Si epilayers. Such a build-up can be explained by the occurrence of random quasi-phase matching in the system

Antiphase domain tailoring for combination of modal and 4¯ -quasi-phase matching in gallium phosphide microdisks

International audienceWe propose a novel phase-matching scheme in GaP whispering-gallery-mode microdisks grown on Si substrate combining modal and 4¯ -quasi-phase-matching for second-harmonic-generation. The technique consists in unlocking parity-forbidden processes by tailoring the antiphase domain distribution in the GaP layer. Our proposal can be used to overcome the limitations of form birefringence phase-matching and 4¯ -quasi-phase-matching using high order whispering-gallery-modes. The high frequency conversion efficiency of this new scheme demonstrates the competitiveness of nonlinear photonic devices monolithically integrated on silicon

Slow-light microcavities

International audienc

Impact of Antiphase Boundaries on Non-linear Frequency Conversion in GaP/Si Microdisks

International audienc