Robust Method of Stabilization of Optical Feedback Regime by Using Adaptive Optics for a Self-Mixing Micro-Interferometer Laser Displacement Sensor

A self-mixing (SM) micro-interferometer laser displacement sensor coupled with an adaptive liquid lens (ALL) system is proposed and implemented. This has been made possible by a new method of real-time estimation of the optical feedback coupling factor C. It is shown that such an estimation of C combined with an appropriate amplification of the SM signal Gain allows the ALL system to seek and maintain the SM signal in the moderate optical feedback regime in spite of variations in the optical feedback. The ALL system thus enables robust real-time displacement sensing in an unmanned autonomous manner. The implemented system has provided measurement precision better than 90 nm for different target surfaces and distances. The paper also investigates the impact of the weighting attributed to C and Gain on the retrieved displacement precision. As this autofocus is presently only performed once during the sensor initialization, so maximum displacement span after achieving optical feedback regime locking has also been investigated and tabulated. This proof of concept, thus paves the way for the deployment of autonomous SM sensors.