Numerical simulation and experimental study of displacement measurement based on self-mixing interference

According to the theory of laser oscillation cavity with three mirrors, a model for displacement measurement using self-mixing interference of semiconductor laser is established in this paper. Using this model the signals of the self-mixing interference due to an external reflector modulated by different waves are theoretically studied. It is shown that the fringe number of output signal, with which the signal changes orientation, is determined by displacement of the reflector. When the reflector moves half wavelength, the signal outputs a whole fringe. Increasing the feedback intensity will enhance the fringe inclination. When the reflector moves smaller, the signals incline on left. When the reflector moves larger, the signals incline on right. The reason of the fringe inclination results from the nonlinear phase in signal intensity impacted by feedback. Above conclusions are the same with arbitrary wave driving reflector. Experimental results are well agreement with theoretical conclusions.