Frequency Compensation for a Self-Mixing Interferometer

Laser interferometry is a well-established technique that is widely used in industrial and laboratory environments to measure displacement, velocity, vibration, and distance. Recently, a new technique based on self-mixing (or feedback) interferometry has been introduced. The operation of this technique is based on a feedback loop controlling the laser pump current. The characterization of the vibrometer shows that the closed-loop performance is frequency dependent in view of the wavelength modulation (WM) dynamics. In this context, this paper addresses the measurement of the frequency response of the WM in a laser diode, for application in a self-mixing interferometer. The WM is derived by the measurement of the interferometric phase, whereas the frequency response is estimated by means of frequency-domain model identification techniques. The estimated frequency response is eventually used to design a frequency compensator for the vibrometer.