Abstract: In order to reduce the interference of common mode noise and improve the SNR (Signal-to-Noise Ratio) of laser self-mixing grating interference signal under the condition of signal loss, a method of measuring the interference displacement of laser self-mixing grating based on differential technology is proposed. The +1 diffraction light is reflected by the vibrating object and returns to the laser cavity, where self-mixing interference occurs and is received by the photodetector PD1 encapsulated in the laser, while the 0 diffraction light is received by the external photodetector PD2 . According to the principle that there is phase difference in the forward and backward output of semiconductor laser, the phase of the self-mixing interference signal carried by the two beams is opposite, and the superimposed noise is partially correlated, so the difference between the two interference signals can eliminate part of the noise. By processing the differential self-mixing signal, the displacement can be reconstructed. The experimental results show that the mean error of the reconstructed vibration waveform is smaller, the signal is more stable, and the signal-to-noise ratio of the interference signal is improved by no less than 3 dB.

Key words: self-mixing interference, diffraction grating, displacement sensing, differential processing