All-fiber hybrid displacement-sensing system based on self-mixing interference and intracavity spectroscopy

Micro-displacement is a classic application of laser self-mixing interference (SMI) measurement system, but most of the current researches are focused on single-channel measurement. In this paper, a dual-channel displacement-sensing system is proposed and demonstrated based on the SMI effect and intracavity spectroscopy. The 90.14-pm/μm sensitivity for the displacement sensing can be achieved when the intracavity spectroscopy is employed to monitoring the output spectra. For the SMI operation mode, the variational mode decomposition (VMD) is used to decompose and reduce the noise of the SMI signal, and the interference fringe counting method is used to reconstruct the displacement of the noise-reduced SMI signal to realize the displacement measurement of the target object. It is demonstrated that the displacement-reconstruction error is 110 nm when the frequency is 30 Hz and the peak-to-peak amplitude is 4 μm.