Mesure de gradients de déformations par fibre optique = Strain gradient measurement with optical fiber

National audienceCet article porte sur l'utilisation de fibre optique à réseau de Bragg pour mesurer des profils de déformations non uniformes. Les réseaux de Bragg permettent facilement de mesurer des déformations uniformes, notre méthode est donc expliquée pour mesurer des gradients de déformations. Cette méthode est ensuite testée sur une éprouvette en résine, et les résultats comparés à une simulation numériques. Des fibres optiques à réseau de Bragg sont ensuite insérés dans des éprouvettes en composites stratifiés afin de caractériser les variations de déformations à travers les plis soumis à des sollicitations de flexion

FIBRE OPTIC SENSORS APPLIED TO RESIN TRANSFER MOLDING: A POWERFUL WAY FOR IN- SITU QUANTITATIVE CONTROL AND OPTIMIZATION

SUMMARY: RTM6 epoxy resin curing is usually characterized by the polymerisation degree. We report in this paper on a refractive index measurement technique applied on an experimental mould to control, quantitatively and in-situ, the industrial RTM process. The calibration of the optic fibre sensor using a specific mould enables a quantification of the RTM6 epoxy resin polymerisation process. It is also very useful to follow the filling of a mould. The recorded data, coupled to PAM-RTM simulations, can be then used to estimate the permeability along one direction. Finally, it is important to underline that the optoelectronic system is connected to a data processing unit and is easy to use in an industrial environment

Pb(Zr,Ti)03 ceramic thick films for optical device applications

International audienceFerroelectric Pb,ZrTi1O3 (PZT) has been prepared by chemical solution deposition (CSD) and spin-coating technique, using acetate and alkoxide precursors. Rapid thermal annealing has been employed in order to obtain crystallization in the perovskite phase. Aiming to study the optical properties of the films, PZT was deposited on different glass substrates. Structural characterization ofthe films was done by X-ray diffraction, morphology was investigated by SEM micrography. Using standard photography analysis, the films were qualified in terms of crack density, their appearance strongly depending on the type of substrate. Using a visible to the near infrared spectrophotometer, the transmittance normal to the surface ofthe films was studied. Coupling oflaser light into the films by the M-lines technique allowed the determination of the refractive index and the thickness of the ferroelectric layer. A waveguiding interferometer structure of Mach-Zehnder type was realized by photolithography and wet chemical etching

High frequency intensity noise measurements applied to semiconductor lasers

International audienc

High frequency intensity noise measurements applied to semiconductor lasers

International audienc

Extrinsic fibre Fabry-Perot interferometer for vibration and displacement measurement: the benefit of polarization decomposition

International audienceWe have successfully developed a new design of an extrinsic fibre Fabry-Perot interferometer (EFPI) sensor dedicated to the characterization of vibration and displacement of a target. This device, based on a low finesse Fabry-Perot cavity formed by the end of a 'sensing' optical fibre and the target, gives information on the direction of the motion without the use of an additional reference arm. The incoming light, emitted by a 1310 nm laser diode, is decomposed according to two orthogonal polarization orientation inside the cavity. The two resulting interference signals are then carried back by the same optical fibre and sent to two photodiodes via a coupler and a polarizing beam splitter. With a relativelysimple signal processing, a precision of lambda/4 is achieved for the measurement of the displacement, for which the direction is also extracted. In addition, one can determine the velocity of the motion, that have been successfully compared with a reference sensor. The use of a polarization maintaining fibre as sensing arm, not mandatory formonitored laboratory set-up, allows the use of this sensor principle even with external perturbation (temperature changes, mechanical stress...)

PHOTODIODE FOR COHERENT DETECTION : MODELING AND EXPERIMENTAL RESULTS

En détection cohérente, la puissance optique de l'oscillateur local peut conduire le photodétecteur en régime de forte injection. Des dégradations de performances du dispositif peuvent alors être constatées à partir de simulations numériques et de mesures.In coherent detection, the optical power of the local oscillator can lead the photodetector in the high injection regime. Degradation of the device performance can then be observed from numerical simulations and experiments

Les photodiodes à avalanche Hg0,4Cd0,6Te à λ = 1,55 μm. Bruit près de la résonance due au couplage spin-orbite

This contribution is devoted to the electrical and optical characterization of three Hg1-xCdxTe avalanche photodiodes from planar technology with composition parameter x near 0.6. This alloy composition leads to devices that are well suited for 1.55 μm detection. From the noise analysis under multiplication we intend to show the tight dependence of the ratio k = β/α - of the hole and electron ionization coefficients respectively — upon the ratio Δ/ Eg or x. It so turns out that in these Hg1- xCdxTe alloys around x = 60 %, Δ is very close to Eg therefore k reaches its maximum value. Due to this physical property, this II-VI alloy may be considered as a good candidate among the semiconductor materials from which 1.3 to 1.6 μm avalanche photodiodes could be made and used in the fibre optics transmission systems [1, 2].L'objet de ce papier est la caractérisation électrique et optique de trois photodétecteurs à avalanche Hg1-xCd xTe de technologie planar pour des compositions x différentes mais très voisines de 0,6 pour adapter ces composants à la photodétection à λ =1,55 μm. On montrera par l'analyse du bruit en régime de multiplication la grande dépendance du rapport k = β/α des coefficients d'ionisation respectivement des trous et des électrons en fonction du rapport Δ/ Eg ou de x. En effet, aux environs de x = 0,6 dans l'Hg1-xCdxTe on est très proche de l'égalité Δ = Eg pour laquelle k passe par un maximum. Cette propriété de ce composé II-VI fait qu'il peut être considéré comme un bon candidat pour la réalisation de photodétecteurs à avalanche dans la fenêtre 1,3 à 1,6 μm pour les télécommunications à fibres optiques [1, 2]