High-speed joint estimation of for strong feedback regime with fringe loss

Abstract

A self-mixing (SM) displacement sensor is very simple and economic in hardware. In order to improve the resolution of the displacement measurement, the optical feedback factor C must be estimated for the phase unwrapping method (PUM). In particular, when the SM sensor operates in a wide range of the C value including the strong feedback regime with fringe loss, the C estimation is necessary even for any consecutive samples based unwrapping (CSU) method or fringe counting method, which does not intrinsically require the C estimation. It is because each fringe of self-mixing signals (SMSs) in such a case does not correspond to the half of the emission wavelength of the laser. The paper proposes a method of the high speed joint estimation of the optical feedback factor and the linewidth enhancement factor in the case of the strong feedback regime with fringe loss, i.e., when C>7.8. Incorporation of the presented approach with those reported by Ri et al. (2020) and Kim (2020) which have presented the immediate C estimation method in a weak regime and a moderate or strong regime without fringe loss, respectively, will give an effective tool to develop a low-cost real-time SM displacement sensor with a better resolution than half-wavelength.