Identification of the Wavelength-Modulation Frequency Response in a Self-Mixing Interferometer

Abstract

Laser interferometry is a well-established technique, widely used in industrial and laboratory environments to measure displacement, velocity, vibration and distance. Usually, this method relies on an external interferometer, i.e., an optical transducer made up of lenses, prisms and mirrors, which is read-out using laser light or white light. Recently, a new technique known as self-mixing (or feedback) interferometry has been introduced, in which a fraction of the light back-reected by a remote target is allowed to re-enter the laser cavity, thus generating a modulation of both amplitude and frequency of the lasing field. The operation of this technique is based on a feedback loop, the design of which requires accurate models of the wavelength modulation dynamics. In this context, this work addresses the measurement of the frequency response of the wavelength modulation in a laser diode, for application in a self-mixing interferometer. The wavelength modulation is derived by the measurement of the interferometric phase, while the frequency response is estimated by means of frequency-domain model identification techniques.