To measure the vibration of a target by laser self-mixing interference (SMI), we propose a method that combines feature extraction and random forest (RF) without determining the feedback strength (C). First, the temporal, spectral, and statistical features of the SMI signal are extracted to characterize the original SMI signal. Secondly, these interpretable features are fed into the pretrained RF model to directly predict the amplitude and frequency (A and f) of the vibrating target, recovering the periodic vibration of the target. The results show that the combination of RF and feature extraction yields a fit of more than 0.94 for simple and quick measurement of A and f of unsmooth planar vibrations, regardless of the feedback intensity and the misalignment of the retromirror. Without a complex optical stage, this method can quickly recover arbitrary periodic vibrations from SMI signals without C, which provides a novel method for quickly implementing vibration measurements.

This study presents a Sagnac loop-based twisted pair microfiber sensor for simultaneous temperature and pressure monitoring. The meticulously engineered microfiber is encapsulated within a polydimethylsiloxane (PDMS) film, enhancing the sensor’s sensitivity and structural stability. This improvement leverages the PDMS high thermo-optic coefficient and low Young’s modulus, along with the strong evanescent field transmission characteristics in the twisted microfiber coupling region and the interference period change in response to external environmental variations. Numerical simulation computations and theoretical modeling further analyze the response performance of the sensor. The experimental results demonstrate that the sensor has a temperature sensitivity of 2.90 nm/°C and a pressure sensitivity of 54.43 pm/Pa. The maximum temperature resolution is 0.0013°C and the maximum pressure resolution is 0.0730 Pa. In addition, the temperature and pressure sensing can be simultaneously demodulated by operating on the cross-sensitivity matrix. The sensor boasts high sensitivity, excellent linearity, a compact structure, and straightforward manufacturing, offering broad application prospects in biochemistry and industrial production.

An enhanced self-mixing interference (SMI) method in a laser diode (LD) based on a Fabry–Perot etalon (FPE) is presented. This method uses uncoated fused silica to form a FPE as a narrowband filter in the LD outer cavity, which can tune the laser wavelength to the edge of the FPE transmission spectrum profile to perform intensity demodulation. We compare the SMI signal based on the FPE filter with the conventional SMI signal. The experimental results show that the amplitude of the SMI signal based on the FPE filter is enhanced about 5 times in the range of 1 µm–5 µm; the displacement reconstruction errors are reduced by 30 nm; and the signal quality is significantly improved.