Joint estimation of self-mixing interferometry parameters and displacement reconstruction based on local...

It is not easy to estimate self-mixing interferometry parameters, namely, the optical feedback factor and the linewidth enhancement factor from the self-mixing signals (SMSs) affected by noise such as speckle. These SMSs call for normalization, which is not only difficult, but also apt to distort the intrinsic information of the signals, thereby resulting in incorrect estimation of the parameters and the displacement reconstruction. In this paper, we present what we believe is a novel normalization method we call "local normalization," which enables more exact and simpler estimation and displacement retrieval compared to previous methods, for it is based on an analytic relation instead of approximation. The method is very noise-proof, and especially speckle-noise-proof as well. The method proposed can be applied to moderate and strong feedback regimes. The simplicity and accuracy of the method will provide a fine tool for a low-cost self-mixing displacement sensor with a high resolution of about 40 nm.