Phase variance reduction of high order Stokes lines in Brillouin fiber lasers

International audienceSummary form only given. Brillouin fiber ring lasers have already been extensively studied and results have shown that the generated first order Stokes wave has less intensity and phase noise than the seeded pump. This increase in coherence is attractive for many sensing applications, whether in the field of fiber sensors or remote sensing systems such as LIDAR. Brillouin fiber lasers with several Stokes components can further increase the coherence through a cascading effect, the 1st Stokes component being the pump for the 2nd Stokes order and so on. In this communication, we investigate the noise properties of a multi-Stokes Brillouin fiber laser. We present numerical simulations from a model that is an extension of the usual three-waves model of stimulated Brillouin scattering in agreement with experimental results

Effect of a noisy driving field on a bistable polariton system

International audienceWe report on the effect of noise on the characteristics of the bistable polariton emission system. The present experiment provides a time-resolved access to the polariton emission intensity. We evidence the noise-induced transitions between the two stable states of the bistable polaritons. It is shown that the external noise specifications, intensity and correlation time, can efficiently modify the polariton Kramers time and residence time. We find that there is a threshold noise strength that provokes the collapse of the hysteresis loop. The experimental results are reproduced by numerical simulations using Gross-Pitaevskii equation driven by a stochastic excitation

Dephasing effects on coherent exciton-polaritons and the breakdown of the strong coupling regime

International audienceUsing femtosecond pump-probe spectroscopy, we identify excitation-induced dephasing as a major mechanism responsible for the breakdown of the strong coupling between excitons and photons in a semiconductor microcavity. The effects of dephasing are observed on the transmitted probe-pulse spectrum as a density-dependent broadening of the exciton-polariton resonances and the emergence of a third resonance at high excitation density. A striking asymmetry in the energy shift between the upper and the lower polaritons is also evidenced. Using the excitonic Bloch equations, we quantify the respective contributions to the energy shift of many-body effects associated with Coulomb fermion exchange and photon assisted exchange processes and the contribution to collisional broadening

Réseau de Bragg fibré pour le filtrage à bande étroite de l'émission autour de 400 nm d'une diode laser InGaN

National audienceNous rapportons la conception de réseaux de Bragg fibrés et présentons le résultat obtenu après montage d'un réseau utilisé comme réflecteur externe d'une diode laser InGaN afin d'en affiner le spectre jusqu'à obtenir une émission monomode longitudinale

Etudes expérimentales des propriétés dispersives de structures photoniques à base de micro-résonateurs pour la réalisation de fonctions optiques

In this thesis, we present a theoretical and experimental study on the dispersive properties of photonic structures based on microresonators. First, we develop a cavity ringdown based method who fully describe the linear properties of microcavities such as coupling regime and group delay. This homodyne method is successfully applied on a cristalline microdisk (MgF2) and passive and active microspherical resonators to characterize various types of phenomena. In the case of doped microspherical whispering gallery modes resonators, we demonstrate selective amplification filter by combining high spectral selectivity and below threhold laser amplification (gain up to 20 dB at 1.55 μm). In passive high-Q microspheres with high finesse (F > 10^5), we could observe a lift of degeneracy between counter propagating modes. This effect originates from Rayleigh scattering that couples these two modes. This phenomenom is observed in the spectral domain by a splitting of the resonance. In a second step, we study the dispersive properties of coupled-resonator architectures. The coupling of two cavities leads to a splitting of the resonance and a notable decrease in the absorption around the resonance. We experimentally show that it is possible to circumvent limitation imposed by the intrinsic losses of passive resonators using active resonators. This effect can be seen as the classical counter part of Electromagnetically Induced Transparency (EIT). Moreover, we demonstrate that Coupled-Active-Resonator-Induced Transparency is a promising alternative in optical delay line since we can dynamically adjust the delay from a few ns to tens of ns (≈ 90 ns) without any change in the transparency of the system. Furthermore, we propose and experimentally demonstrated tunable cavity-linewidth narrowing based on the strong dispersion induced by the coupling of two resonators. In the case of three resonators, we propose a coupling scheme allowing the Q-factor of a critically coupled resonator to be increased and actively modulated by using two additional coupled resonators. We experimentally validate the principle by means of a model system consisting of Er3+-doped fiber coupled resonators. We successfully show a growth of the Q-factor from 4×10^7 up to 2,5×10^8. These experimental results demonstrate the means of Q-factor tailoring using active artificial photonic media.La caractérisation de résonateurs de facteurs de surtension très élevés (> 10^8) est difficilement réalisée à partir des méthodes expérimentales conventionnelles en régime stationnaire. Nous proposerons une méthode hybride spectrale/temporelle permettant la mesure du facteur de surtension global et la discrimination, de manière univoque, des facteurs Q_0 intrinsèque et Q_e extrinsèque du dispositif. Par cette simple mesure, nous déterminons le régime de couplage et les propriétés dispersives de micro-cavités. Dans un second temps, nous présenterons différentes architectures à base de cavités couplées actives donnant accès un à degré de liberté supplémentaire quant au contrôle de la dispersion. Nous étudierons successivement le phénomène de transparence induite pour la réalisation d'états de lumière lente puis la dispersion induite dans le cas de deux et trois cavités. Dans ce dernier cas, la modulation des pertes intrinsèques mène à un contrôle actif du facteur de qualité de la structure. La démonstration expérimentale de ce principe montre la possibilité d'ingénierie du facteur Q par l'utilisation de structures photoniques artificielles actives

Microcavité non linéaire sous contrôle cohérent

6 pagesNational audienceLes microcavités non linéaires, dont les applications sont très variées en raison de leur haut facteur de confinement du champ, ont permis d'abaisser significativement les puissances de commande de composants pour le traitement tout optique du signal. Cependant, les effets non linéaires induisent un désaccord entre la fréquence de résonance de la cavité et le signal d'excitation, ce qui limite, par un phénomène de battements, l'énergie couplée dans le résonateur. Nous proposons ici une méthode, basée sur un contrôle de la relation temps-fréquence de l'impulsion d'entrée, permettant d'augmenter l'énergie couplée dans une microcavité semi-conductrice

High-Q Microresonators: Characterization Method and Application to Amplifying Optical Delay Lines

We present ringing phenomenon in coupled resonators and in high-Q amplifying whispering gallery mode resonators. This effect can be used to measure the gain and the group delay of optical integrated delay lines

Brillouin Gain Characterization by Cavity Ringdown Spectroscopy

International audienceNowadays, narrow linewidth lasers are unavoidable tools for fundamental and applied physics. One promising approach to generate coherent laser emission is based on stimulated Brillouin scattering (SBS) optical nonlinearity. Implementing SBS in an optical cavity gives rise to coherent emission with impressive performances in terms of noise and linewidth. Cascading the SBS process can even, under given conditions, improves the coherent emission specifications. To achieve such performances it is crucial to determine the Brillouin gain coefficient. Usual pump-probe methods are carried out in single pass waveguides. The probe intensity is proportional to e gBP in L eff / A eff where P in is the incident pump power, A eff the effective mode area and L eff the usual effective interaction length. To observe significant probe amplification one needs either long waveguides or strong pump power to reach the SBS threshold. We propose a method, based on the cavity ringdown spectroscopy, to directly characterize the Brillouin gain coefficient inside a resonator. This configuration allows to extract Brillouin parameters from the light recirculation with both a reduced waveguide length and input pump power when compared to usual methods

Ringing phenomenon in coupled cavities: Application to modal coupling in whispering gallery mode resonators

International audienceWe present a simple model to describe the transient response of two coupled resonators probed by a monochromatic wave whose frequency is rapidly swept across the resonances with respect to their characteristic photon lifetimes. The model is applied to analyze the dynamic behaviour of the modal coupling between two degenerate resonances of the same cavity. In particular, this can be used to describe the coupling of counter propagating whispering gallery modes (WGMs) by Rayleigh scattering. The theory is successfully compared to experiments carried out in silica microspheres. These results show that this ringdown technique can be extended to accurately measure linear properties and frequency splittings of high-quality factor WGM micro-resonators

High-Q passive and active microresonators for dispersion and delay line applications

conference 7612 " Advances in Slow and Fast Light III ", Topic " Advanced Quantum and Optoelectronic Applications ", Session 7 " Slow Light in Microresonators and Semiconductor Structures " [7612-25], http://spie.org//x39144.xmlInternational audienceWe theoretically analyze the light-storing process in optical microresonator arrays. We propose a passive and an active scheme to strongly slow light. The two mechanisms rely on microresonator chains whose high order dispersion is optimized. The unit cell of the systems is a short sequence of two or four resonators. In the passive process we show that the cancellation of the third order of dispersion allows the propagation of short pulses with no significant distortion in a microresonator array. The second process needs the use of active microresonators whose loss and gain are dynamically tuned. The structure is made of only four resonators and is optimized to avoid pulse distortion as it is the case in the passive scheme. The loss and gain modulations allow the resonant structure to be isolated from the access waveguide and optical pulse to be stored