All-fiber laser self-mixing interferometry for signal enhancement with phase-shifted fiber Bragg grating

In this paper, phase-shifted fiber Bragg grating (PSFBG) is introduced in an all-fiber laser self-mixing interferometry (SMI) for signal enhancement. PSFBG is used as an optical filter to enhance the signal to noise ratio (SNR) of SMI signal. When the laser wavelength locates at the edge of the filter, the frequency modulation (FM) can be mapped to the easy-to-detect amplitude modulation (AM) to enhance the SMI signal. Simulation and experimental comparison of unenhanced SMI signal, FBG-enhanced SMI signal and PSFBG-enhanced SMI signal are presented. The enhancement effects of different reflectivity surfaces are comparatively analyzed and the maximum spatial test ranges of lower reflectivity surfaces are compared between unenhanced and PSFBG-enhanced. As well as applying the PSFBG-enhanced to the Doppler effect experiment. Due to the extremely narrow linewidth of PSFBG , the PSFBG-based SMI has the better performance in longer detection range and lower backscattering light. PSFBG-enhanced achieves an impressive enhancement of up to 800 times compared to unenhanced signals.