Laser self-mixing interferometry for dynamic displacement sensing of multiple targets

A multichannel laser self-mixing interferometry (SMI) is proposed based on a combination of linear injection current modulation and carrier frequency division multiplexing (FDM) technique. The laser output is split into several beams with each beam directed toward a specific target for measurement. The reflected beams then return to the laser cavity, where self-mixing interference takes place. Since the external cavity length of each measurement channel is different, the SMI signal contains multiple carriers due to the injection current modulation. An algorithm based on FDM is developed for displacement sensing of multiple targets from a single SMI signal. Experimental results show that the relative error of multichannel displacement measurement is <1.4%. This work demonstrates an attractive multichannel SMI for displacement sensing featuring compact configuration and high resolution.