Improving the performance of optical feedback self-mixing interferometry for vibration measurement

Optical feedback self-mixing interferometer (OFSMI) is an optoelectronic system that makes use of the self-mixing interferometric effect of semiconductor lasers (SLs). When a small portion of the light emitted by a laser diode (LD) is reflected or back scattered by an external object and re-enter the laser cavity, the reflected light will interfere with the light inside the cavity which causing the variance of the overall laser intensity emitted by the LD. During the past decades, this physical phenomenon has been studied extensively and many possible applications have been investigated. A major application is the measurement of metrological quantities associated with the external object, including the displacement, the speed, the vibration parameters, and so on. A well known conclusion regarding the OFSMI based measurement is that the accuracy or resolution is limited by with the simple OFSMI setup with constant driving current for the LD and without adding other extra optic components. This thesis aims to report on the research work which tries to improve the performance in terms of accuracy of OFSMI systems. In particular, novel techniques are demonstrated that enable simple OFSMI systems to higher accuracy beyond the limitation for displacement measurement. Also new techniques for measuring the linewidth enhancement factor (LEF) and feedback level factor (C) of the LD are developed. In order to achieve these target, various novel techniques have been proposed and implemented, including the data-fitting principle for displacement estimation, genetic algorithms for estimating multiple parameters of OFSMI systems, phase-unwrapping algorithm for OFSMI signals and data preparation methods.