Signal extraction method based on spectral processing for a dual-channel SMI vibration sensor

Laser self-mixing interferometry (SMI) is a powerful measurement technique with high sensitivity and subwavelength precision. However, the simultaneous detection of multi-targets with adjacent frequencies for current SMI systems is an enormous challenge because their spectra are overlapped to be distinguished difficulty. Here, a novel method based on the short-time Fourier transform (STFT) and pre-feedback structure is presented for dual-channel laser SMI, which realizes the recovery of two vibrations with adjacent frequencies. The spectrum of the SMI signal is expanded along the time-axis by STFT, in which the pre-feedback mirror is applied to reallocate the energy of each channel. Further, the signal is extracted separately through spectrum suppression and transformation. Simulation results show that the proposed approach is effective in vibration frequencies over a large range of ratio of 1:1- 1:5 in the weak feedback regime. The RMS errors of the experimental results with less than 11.29 nm (0.87%) indicate the reliability of this scheme, which provides an alternative solution for the simultaneous detection of multi-parameters.