Nouvelles architectures de réseaux résonants pour la stabilisation de diodes laser

L'étude porte sur la stabilisation spectrale de diodes laser par des cavités externes incorporant un filtre à réseau résonant. La première partie des travaux concerne la modélisation de la cavité externe et les critères requis sur les caractéristiques d'un filtre pour obtenir une émission monomode. La conception et la réalisation de différents réseaux, utilisés en montage de type Littrow, permettent d'obtenir une stabilisation de diodes conventionnelles avec un SMSR supérieur à 30dB, tout en étant très sensible aux désalignements, en raison de la faible tolérance angulaire de ces filtres. La seconde partie concerne de nouveaux types de filtres, dont le réseau résonant est encadré par 2 réseaux latéraux de demi-période. Ces filtres présentent une grande tolérance angulaire proche de 10°, associée à une largeur spectrale nanométrique, qui autorise un montage en œil de chat, compact et facile à mettre en œuvre, tout en obtenant une stabilisation spectrale avec un SMSR supérieur à 30dB.Our study deals with the spectral stabilization of laser diodes by external cavities incorporating a resonant grating filter. The first part of this work concerns the theoretical study of the external cavity and the criteria required for the characteristics of the filter to obtain a monomode emission. The conception and the realization of the different gratings, used in Littrow-like configuration, enable us to stabilize conventional laser diodes with a SMSR above 30dB, though being very sensitive to misalignments due to low angular tolerance of these filters. The second part concerns new types of filters, whose resonant grating is surrounded by two lateral reflectors with half-period. These filters have a wide angular tolerance close to 10°, combined with a nanometric bandwidth, that authorizes a cat's eye configuration, compact and easy to get working, all the while obtaining a spectral stabilization with a SMSR above 30dB

Anisotropic super-attenuation of capillary waves on driven glass interfaces

Metrological AFM measurements are performed on the silica glass interfaces of photonic band-gap fibres and hollow capillaries. The freezing of attenuated out-of-equilibrium capillary waves during the drawing process is shown to result in a reduced surface roughness. The roughness attenuation with respect to the expected thermodynamical limit is determined to vary with the drawing stress following a power law. A striking anisotropic character of the height correlation is observed: glass surfaces thus retain a structural record of the direction of the flow to which the liquid was submitted

Nondestructive measurement of the roughness of the inner surface of hollow core-photonic bandgap fibers

We present optical and atomic force microscopy measurements of the roughness of the core wall surface within a hollow core photonic bandgap fiber (HC-PBGF) over the [3×10-2 µm-1 to 30 µm-1] spatial frequency range. A recently developed immersion optical profilometry technique with picometer-scale sensitivity was used to measure the roughness of air-glass surfaces inside the fiber at unprecedentedly low spatial frequencies, which are known to have the highest impact on HC-PBGF scattering loss and, thus, determine their loss limit. Optical access to the inner surface of the core was obtained by the selective filling of the cladding holes with index matching liquid using techniques borrowed from micro-fluidics. Both measurement techniques reveal ultralow roughness levels exhibiting a 1/f spectral power density dependency characteristic of frozen surface capillary waves over a broad spatial frequency range. However, a deviation from this behavior at low spatial frequencies was observed for the first time, to the best of our knowledge

Flagfolds

By interpreting the product of the Principal Component Analysis, that is the covariance matrix, as a sequence of nested subspaces naturally coming with weights according to the level of approximation they provide, we are able to embed all $d$--dimensional Grassmannians into a stratified space of covariance matrices. We observe that Grassmannians constitute the lowest dimensional skeleton of the stratification while it is possible to define a Riemaniann metric on the highest dimensional and dense stratum, such a metric being compatible with the global stratification. With such a Riemaniann metric at hand, it is possible to look for geodesics between two linear subspaces of different dimensions that do not go through higher dimensional linear subspaces as would euclidean geodesics. Building upon the proposed embedding of Grassmannians into the stratified space of covariance matrices, we generalize the concept of varifolds to what we call flagfolds in order to model multi-dimensional shapes

Nouvelles architectures de réseaux résonants pour la stabilisation de diodes laser

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Graded CRIGF filters for tunable external cavity lasers

International audienceGraded CRIGF filters were fabricated and characterized. When inserted in a three elements cat’s eyes laser diode external cavity, they allow continuous tuning of the emission wavelength over 20 nm in the 850 nm range