Étude de diodes lasers pour des applications métrologiques de la rétro-injection optique

Analysis of semiconductor laser for sensing applications using the self-mixing effect

• Auteur / Autrice : Gregory Mourat
• Direction : Marc Lescure
• Type : Thèse de doctorat
• Discipline(s) : Électronique
• Date : Soutenance en 1999
• Etablissement(s) : Toulouse, INPT

Mots clés

Mots clés contrôlés

Spectres

Télémétrie

Diodes laser

Résumé

Le phénomène de ''self-mixing'' (interférences à deux ondes dans le milieu actif d'une diode laser) est utilisé pour des applications métrologiques telles que la mesure de distance, de déplacement ou de vitesse. Dans ces dispositifs, une diode laser émet un faisceau en direction d'une cible. Une partie de l'onde lumineuse est réfléchie en direction du laser et perturbe la puissance d'émission. L'information métrologique recherchée est alors déterminée en traitant ces variations de puissance. Dans la première partie (ch. I à III), les limitations intrinsèques des interférences par self-mixing dues à la source laser sont étudiées. La seconde partie (ch. IV à VI) a pour objectif de déterminer les critères prépondérants au choix de la source laser à utiliser pour chaque application métrologique du self-mixing.

The self-mixing interference is used for sensing applications like distance, displacement or velocity measurements. In such a set-up, interference occurs into the laser cavity between the beam inside this cavity and the beam back-scattered from a mirror-like or a rough target in front of the laser. Variations of the optical output power caused by this interference can be used to determine relative or absolute distances. In the first part of this manuscript (chapter I to III), self-mixing limitations due to the laser source are exhibited. Like for classical interference, the phenomenon can only be used for a target located at a distance smaller than the half coherence length. However, the self-mixing effect is quite different from classical interference as the coherence properties of the laser source are modified by the distance to the target and its reflection coefficient. The range of a relative or absolute distance sensor, developed in our laboratory, is then determined in terms of the spectral characteristics of laser sources. In the second part, the choice of the laser sources is optimised in function with each sensing application of the self-mixing effect. In chapter IV and V, the stability and the spectral behaviour of Fabry-Perot laser diode are analysed. The proposed semiclassical theory shows that multi-quantum well lasers emitting around 800 nm are the best choice for both self-mixing applications. Chapter VI presents different exotic laser structures which can be of great interest for self-mixing sensors. A 3 electrodes DBR laser diode has been used for distance measurement, a resolution of 0. 5 mm being reached for a range between 20 to 60 cm. Finally, a new self-mixing range finder has been designed with a real-time chirp control, using an all-optical fibre Mach-Zender interferometer. A resolution of 50 µm has been obtained at a distance of 10 cm.