Simulation numérique de la propagation d'une source laser incohérente dans une fibre optique

International audienceLe présent travail concerne les lasers à fibre impulsionnels de puissance de type MOPFA (oscillateur laser maître suivi d'un amplificateur à fibre). Un travail expérimental a permis d'établir que les non-linéarités observées (effet Kerr, mélange à quatre ondes, effet Raman) pouvaient être de nature très différentes selon les caractéristiques de la source issue du laser maître sans toutefois permettre de déterminer si la statistique des photons est seule responsable des différents scénarios non-linéaires observés. Nous avons développé un code de simulation numérique afin de pouvoir valider l'hypothèse selon laquelle les propriétés du laser maître en termes de cohérence jouent un rôle prépondérant dans la manifestation des non-linéarités

First demonstration of a 12 DFB fiber laser array on a 100 GHz ITU grid, for underwater acoustic sensing application

International audienceWe report for the first time a multiplexed array of 12 distributed feedback fiber lasers (DFB FLs) on a single optical fiber, separated by only 100 GHz (0.8 nm) in the C-band. These lasers are pumped by a 200 mW laser diode at 1480 nm with no apparent impact on the sensor noise floor despite the fact that the residual reflections from adjacent gratings may be enhanced due to the smaller wavelength separation. Each DFB FL, especially developed for serial multiplexing, exhibits low lasing threshold typically between 1 and 2 mW, low intensity noise and very low frequency noise (less than 30 dB re 1 Hz²/Hz at 1 kHz from optical carrier). From these experimental results, extension to 32 DFB FLs array (on 100 GHz ITU grid) multiplexed on one fiber will be discussed

Effets d'une faible contre-réaction optique sur des lasers à fibre DFB pour applications capteurs

National audienceNous étudions l'effet d'une faible réflection externe sur des lasers à fibre à contre-réaction répartie (DFB FLs). Nous démontrons expérimentalement que la phase optique accumulée sur un aller-retour dans la cavité étendue et la réflectivité associée au miroir externe modifient la puissance de sortie et la fréquence d'émission d'un DFB FL. Comme pour un laser à semiconducteurs (SC) contre-réactionné, à réflectivité externe donnée, l'amplitude des variations est constante pour ces deux paramètres quelle que soit la longueur de la cavité externe

Ni/Bi bilayers: The effect of thickness on the superconducting properties

Nickel/Bismuth (Ni/Bi) bilayers have recently attracted attention due to the occurrence of time-reversal symmetry breaking in the superconducting state. Here, we report on the structural, magnetic and electric characterization of thin film Ni/Bi bilayers with several Bi thicknesses. We observed the formation of a complex layered structure depending on the Bi thickness caused by the inter-diffusion of Bi and Ni which leads to the stabilization of NiBi$_{3}$ at the Bi/Ni interface. The superconducting transition temperature and the transition width are highly dependent on the Bi thickness and the layer structure. Magnetoelectric transport measurements in perpendicular and parallel magnetic fields were used to investigate the temperature-dependent upper critical field within the framework of the anisotropic Ginzburg-Landau theory and the Werthamer Helfand Hohenberg model. For thicker samples, we observed a conventional behavior, similar to that shown by NiBi$_{3}$ bulk samples, including a small Maki parameter ($\alpha_{M}$ = 0), no spin-orbit scattering ($\lambda_{SO}$= 0) and nearly isotropic coherence length ($\gamma$ = $\xi_{\perp}$(0)/$\xi_{\parallel}$(0) $\approx$ 1). The values obtained for these properties are close to those characterizing NiBi$_{3}$ single crystals. On the other hand, in very thin samples the Maki parameter increases to about $\alpha_{M}$ = 2.8. In addition, the coherence length becomes anisotropic ($\gamma$ = 0.32) and spin-orbit scattering ($\lambda_{SO}$= 1.2) must be taken into account. Our results unequivocally show that the properties characterizing the superconducting state in the Ni/Bi are strongly dependent on the sample thickness.Comment: 16 Pages and 5 figure

Méthode spectrale quasi-statique efficace pour la modélisation en intensité de la diffusion Raman stimulée

session affiches A8 " Effets non linéaires " [A8.10]National audienceNous proposons une méthode efficace pour la modélisation quasi-statique en intensité de la propagation d'un spectre optique soumis à la diffusion Raman stimulée dans une fibre optique. Le modèle présenté offre un gain de temps de calcul d'un ordre de grandeur pour l'étude de la propagation d'impulsions de largeurs temporelles supérieures à la dizaine de nanosecondes

Variable Optical Attenuator based on thermally tuned Mach-Zehnder Interferometer within a twin core fiber

International audienceA variable optical attenuator (VOA) based on a tunable Mach-Zehnder interferometer has been produced based on a twin core fiber design. Two achromatic 3 dB-couplers have been manufactured utilizing the fused-stretched technique between both cores of the fiber, in order to obtain a Mach-Zehnder interferometer. A metallic thin layer deposit on one arm of the interferometer allows thermal tuning of the Mach-Zehnder interferometer, which obtains the desired attenuation at the component output. We obtained a −0.5 to −24 dB attenuation-range VOA with an achromatic response from 1535 to 1560 nm

20 ns smooth pulse generation in single mode actively Q-switched double clad Yb-doped fiber laser

Topic CJ " Fibre and Guided Wave Lasers and Amplifiers ", session P " Posters " [CJ.P.30]International audienceWe theoretically and experimentally study smooth and short pulse generation in Q-switched Ytterbium-doped fiber laser. 20 ns pulses, with 115 microjoules energy at 20 kHz, are reached for the first time in single mode configuration

Time-resolved spectral analysis for nonlinear effects characterization in pulsed lasers

conference 7728 " Nonlinear Optics and its Applications ", oral session 6 " Nonlinear Optics for Telecommunications " [7728-27]International audienceWe demonstrate a simple method to measure the evolution of nonlinear effects along a pulse. An all-fiber acousto-optic modulator is synchronized to the pulse emission and inserted between the laser output and an optical spectrum analyzer. Thanks to this configuration, the application of a short modulator opening time (10 ns typically) compared to the pulse width (100 ns typically) forms a spectral measurement window. This window is shifted along the pulse by the use of a variable trig delay. The optical spectrum is measured for each position of the window. The nonlinear effects evolution versus the instantaneous power can be characterized. To validate our method, we have analyzed the spectral evolution along 100 ns pulses from different fiber laser sources. We have observed that the spectral broadening due to Kerr effect appears first. Raman scattering occurs next for window positions corresponding to highest peak powers. Finally during the trailing edge course, nonlinear effects disappear in the reverse order of their apparition. This method has also been extended to measure the power inside and outside a pulse in order to deduce the rate of amplified spontaneous emission

Etude de cavités laser fibrées monomodes transverses pour la génération d'impulsions dans la gamme 20-50 ns

session orale Lu1 " Amplificateurs et Lasers à fibre I " [Lu1.5]National audienceLe présent article traite de l'étude et de la réalisation de lasers à fibre, monomodes transverses, fonctionnant en régime déclenché à 1064 nm. L'analyse porte sur l'influence du type de fibres et du type de cavités utilisées sur la durée et l'énergie des impulsions. Ainsi, pour la première fois à notre connaissance, des impulsions d'une durée de 20 ns pour une énergie de 115 µJ sont atteintes, à une cadence de 20 kHz