Research and modeling of an electro-absorption modulator for signals of radio over fiber transmission applications UWB frequencies centimétriques. System simulation and characterization of a radio over fiber link to external modulation

Ce travail de thèse, consiste à étudier les performances d'une liaison Radio sur Fibre simplifiée mettant en ¿uvre une modulation extérieure de la source optique avec des signaux OFDM. La source laser est couplée sur une même puce avec un modulateur à électro-absorption, développée par Alcatel III-V LaB été modélisée à l'aide du logiciel ADS( Advanced Design System) et caractérisée au laboratoire.Dans une première partie, nous présenterons une introduction de la technologie Radio sur Fibre avec ses applications, et son intérêt pour les technologies futures.Dans une seconde partie, nous nous intéresserons à la modélisation électrique du modulateur à électro-absorption utilisée pour effectuer la modulation numérique de type OFDM.Dans une troisième partie, sera proposée un modèle complet de la chaine de transmission intégrant tous les composants de la liaison, de manière à effectuer une analyse comportementale du système.La quatrième partie, présentent les performances mesurées réalisées au laboratoire sur le banc de caractérisation de la chaine en modulation numérique OFDM Ultra Large Bande et simulées sous ADS et les corrélations entre les résultats.This thesis is to study the performance of a radio link over fiber simplified implementing an external modulation of the optical source with OFDM signals. The laser source is coupled on a single chip with an electro-absorption modulator, developed by Alcatel III-V LaB been modeled using software ADS (Advanced Design System) and characterized in the laboratory. In the first part, we will present an introduction to the Radio on Fiber technology with its applications, and its interest in future technologies.In the second part, we will focus on the electrical modeling of the electro-absorption modulator used to make the digital OFDM type. In the third part, will be offered a complete model of the transmission chain incorporating all components of the link, so as to perform behavioral analysis system. The fourth part, have measured performance in the laboratory on the chain of characterization bench in digital OFDM Ultra Wideband and simulated in ADS and correlations between the results

Etude et modélisation d'un modulateur à électro-absorption pour des applications de transmission radio sur fibre de signaux ULB aux fréquences centimétriques. Simulation système et caractérisation d'une liaison radio sur fibre à modulation externe

This thesis is to study the performance of a radio link over fiber simplified implementing an external modulation of the optical source with OFDM signals. The laser source is coupled on a single chip with an electro-absorption modulator, developed by Alcatel III-V LaB been modeled using software ADS (Advanced Design System) and characterized in the laboratory. In the first part, we will present an introduction to the Radio on Fiber technology with its applications, and its interest in future technologies.In the second part, we will focus on the electrical modeling of the electro-absorption modulator used to make the digital OFDM type. In the third part, will be offered a complete model of the transmission chain incorporating all components of the link, so as to perform behavioral analysis system. The fourth part, have measured performance in the laboratory on the chain of characterization bench in digital OFDM Ultra Wideband and simulated in ADS and correlations between the results.Ce travail de thèse, consiste à étudier les performances d'une liaison Radio sur Fibre simplifiée mettant en ¿uvre une modulation extérieure de la source optique avec des signaux OFDM. La source laser est couplée sur une même puce avec un modulateur à électro-absorption, développée par Alcatel III-V LaB été modélisée à l'aide du logiciel ADS( Advanced Design System) et caractérisée au laboratoire.Dans une première partie, nous présenterons une introduction de la technologie Radio sur Fibre avec ses applications, et son intérêt pour les technologies futures.Dans une seconde partie, nous nous intéresserons à la modélisation électrique du modulateur à électro-absorption utilisée pour effectuer la modulation numérique de type OFDM.Dans une troisième partie, sera proposée un modèle complet de la chaine de transmission intégrant tous les composants de la liaison, de manière à effectuer une analyse comportementale du système.La quatrième partie, présentent les performances mesurées réalisées au laboratoire sur le banc de caractérisation de la chaine en modulation numérique OFDM Ultra Large Bande et simulées sous ADS et les corrélations entre les résultats

Vibration-based fault detection of sharp bearing faults in helicopters

International audienceMany signal processing tools have been developed by the mechanical and signal processing community to find the characteristic symptoms of sharp bearing faults (like localized spalling) from vibratory analysis. However the context of helicopter imposes a limited sampling frequency regarding the observed phenomena, many noisy vibrations and flight regimes. The performances of the classical methods are limited in such an environment mainly in identifying fault frequencies. Local bearing faults induce temporal periodic and impulsive patterns that produce redundant harmonics in the spectral domain. In this article four methods are proposed to take advantage of that redundancy. These methods provide an estimator of the fault frequency and an indicator of the quality of that estimation. These indicators are used to assess the severity of the fault. The four methods are then tested on synthesized and flight data in order to illustrate and discuss their efficiency

Vibration-based fault detection of meshing shafts

International audienceIn this article, vibration-based monitoring of cracked shafts is addressed in the context of mechanical transmission of helicopters. The approach developed is based on the detection of cyclostationary components produced by a crack. The cyclostationary theory is first presented on a mechanical point of view. Then a signal processing indicator, the spectral coherence, is introduced in order to quantify the second order cyclostationary content of a signal. The characteristics of the vibration produced in the faulty case are explained from a mechanical model of a cracked shaft. It is then shown that small variations in the structural parameters of the crack creates cyclostationary modulations around the meshing frequencies. This justifies the spectral coherence as a relevant indicator to monitor the crack. The spectal coherence is successful applied on bench data reproducing a crack propagation on an actual helicopter shaft

Vibration-based monitoring of helicopter epicyclical gears

International audienceEpicyclical gears in helicopters are the most sophisticated part of the mechanical transmission monitored. This is a result of its numerous sub-components and its low accessibility for sensor mounting and finally, its complex, dynamical behavior. Some analytical and finite element models have suggested to anticipate the vibratory response. However, the external forces that apply to the system during the flight, and the com- plexness of the mechanical design and the multiple power transfer paths, make it quite difficult to make an accurate prediction of the vibratory response received by the accelerometer. Utilizing this prediction for a condition monitoring purpose would lead to poor performances. For this reason, a signal oriented model of vibrations for epicyclical gears is preferred. This model allows for the anticipation of the influence of some damages. Two indicators are proposed to detect the presence of a crack similar to that of a transverse crack on the carrier. The first one uses the cyclic coherence and the second one takes advantage of cyclostationary component separation. These indicators are then tested on data recorded from an Eurocopter's testing rig and have allowed the tracking of the growth of the crack