Quadrature demodulation based on lock-in amplifier technique for self-mixing interferometry displacement sensor

A new self-mixing interferometry quadrature demodulation method based on a lock-in amplifier technique is proposed. Sinusoidal phase modulation of the beam is obtained by an electro-optic modulator (EOM) in the external cavity. Then the real phase of the external target can be calculated by lock-in amplifier analysis method. In this paper, the validity of the proposed method is confirmed by theoretical analysis and means of simulated signals, and then it is demonstrated by several experimental measurements for target harmonic and arbitrary motion. The results show that the proposed method can get a high-precision measurement, even using a diffusive target.