Simultaneous measurement of vibration and parameters of a semiconductor laser using self-mixing interferometry.

Laser diode (LD)-based self-mixing interferometry (SMI) is a promising technique for noncontact sensing and its instrumentation. According to the well-known Lang-Kobayashi equations, an SMI waveform is shaped by multiple parameters, including linewidth enhancement factor (denoted as α), optical feedback level factor (denoted as C), and the movement of the external cavity of an LD. This paper presents a new algorithm for simultaneously retrieving the multiple parameters from a piece of SMI signal. First, a set of linear equations is derived based on the existing SMI model. By careful selection of data samples, the linear equations can be made independent and used to determine a set of variables, and thus the values of α and C, as well as the reconstruction coefficients of the external movement. The work in this paper lifts the restrictions existing in SMI-based sensing methods, such as prerequisite knowledge of either α and C or vibration information of an external target. Simulations and experiments are conducted to verify the proposed algorithm.