Fig. 1. Soft threshold and hard threshold functions

Fig. 2. Signal processing flowchart

Fig. 3. Experimental setup for laser self mixing interference

Fig. 4. Modulation voltage of PZT and experimental SMI signal

Fig. 5. Low frequency approximation coefficients and high frequency detail coefficients of wavelet decomposition

Fig. 6. Comparison of SMI local signals after wavelet threshold filtering

Fig. 7. Peak valley detection of SMI signals based on wavelet threshold filtering

Fig. 8. Peak finding diagram of SMI signal after combining wavelet threshold filtering and S-G filtering

Fig. 9. Comparison of normalized displacement and normalized PZT driving voltage for SMI denoising using wavelet hard thresholding, wavelet soft thresholding, wavelet soft thresholding with S-G filtering