Self-mixing sensor for real-time measurement of harmonic and arbitrary displacements

A real-time self-mixing laser displacement sensor is presented that uses a fast consecutive-samples based unwrapping algorithm. The processing is achieved at a rate of 125KHz by an integrated micro-converter (ADuC7020) embedded on the SM sensor. Arbitrary and harmonic displacements have been measured in real-time with λ /10 precision as compared with the reference built-in capacitive feedback sensor of the target, where λ is the laser wavelength. The algorithm does not require any parameter estimation or huge memory and corrects possible false fringe detections. This results in a compact, integrated, precise and self-aligned laser sensor that costs less than 40 $.