Fast estimation of feedback parameters for a self-mixing interferometric displacement sensor

Self-mixing interferometry (SMI) is an attractive sensing scheme increasingly used for distance, velocity, flow and vibration sensing for applications such as rotational speed of servo drives, detection of single micro-particles in airflow, size measurement of Brownian particles, terahertz imaging etc. In order to retrieve target displacement information with sub-wavelength precision from the SMI signal, two key SMI parameters, namely optical feedback coupling factor C and line-width enhancement factor alpha need to be estimated. In this paper, we propose a fast method to jointly estimate C and alpha parameters in the context of SMI laser displacement sensor. For this purpose, we apply Newton's algorithm to quickly converge to the optimum C and alpha values. Compared to previous methods, this new method enables us to significantly reduce the computation time of parameter estimation and could play a vital role in the development of real-time self-mixing interferometric sensors with sub-wavelength precision.