Spectral Processing of Self-Mixing Interferometric Signal Phase for Improved Vibration Sensing Under Weak- and Moderate-Feedback Regime

I. INTRODUCTIONLASER Diode (LD) based Self-Mixing (SM) or optical feedback interferometry (OFI) [1, 2] is an attractive sensing scheme due to the compact, self-aligned, and low-cost nature of the SM sensor.An SM sensor is much simpler than conventional interferometers because many optical elements such as the beam splitter, reference mirror and external photodetector are not required (Fig. 1 shows a typical SM sensor set-up).Thus, with a simply constructed opto-electronic system, smart laser sensors have been developed using SM [1,2].However, as opposed to traditional interferometers, recovery of displacement from the SM signal is not straightforward due to the complex nature of SM signals involving hysteresis and strongly non-linear fringes (see Fig. 2).Displacement sensing with a resolution of half-wavelength λ0/2 can be easily achieved with a basic SM sensor under