Variable Optical Feedback-Based Behavioral Model of a Self-Mixing Laser Sensor

In this paper, a unified behavioral model of laser feedback based self-mixing interferometry (SMI) is proposed which is able to accurately model the SMI sensor signals encountered under experimental variable optical feedback conditions. The model provides correct SMI signals whether feedback is varied in a continuous or discrete manner, while spanning all major feedback regimes (such as weak-, moderate-, and strong-feedback regime) used for sensing applications. As a result, the proposed model allows the simulation of SMI signals in the presence of speckle which is of upmost importance to develop future efficient algorithms to reconstruct target displacements. The optical speckle usually occurs when the target of comparable surface roughness to the laser wavelength is moving as it induces variation of the optical feedback factor. The proposed model is shown to be able to address such cases and in particular to be able to reproduce very similar SMI signals to those acquired in the presence of speckle. It is thus anticipated that the proposed model would facilitate the design and testing of novel SMI algorithms and systems dedicated to the processing of variable optical feedback based SMI signals for metric sensing applications.