Mesures interférométriques pour les systèmes embarqués Simulation de l’effet d'interférence par rétro-injection optique dans les lasers

Abstract

Optical feedback (or "self-mixing") is an interferometric measurement technique based on the phenomenon of optical feedback into a laser diode cavity. When the laser illuminates a target, a small fraction of the reflected light returns to the active region of the laser cavity, altering its spectral properties. The physical model employed describes the optical coupling between two Fabry-Pérot-type cavities: the primary cavity to the gain medium, while the second is formed by the output mirror and the target. This inherently self-aligning principle eliminates the need for optical components typically required in conventional interferometry, thereby reducing the system's size and cost. The technique relies on the perturbation of the spectral properties of a single-mode laser diode subjected to optical feedback, enabling the measurement of various physical quantities such as distance, velocity, and displacement. Drawing on semiconductor laser dynamics, we present a theoretical model based on the Lang-Kobayashi equations. Solving this system of equations demonstrates that laser intensity modulation—both with and without feedback—depends on the target's effective reflectivity (determined by the target material) and the distance between the laser and the target.