Enhanced vibration measurement through frequency modulated laser diode self-mixing interferometry

Self-mixing interference (SMI) has emerged as a powerful non-contact vibration sensing technique, leveraging the inherent coupling between laser emission and external optical feedback. However, conventional SMI systems often face limitations in signal resolution and measurement accuracy, particularly when probing low-amplitude vibrations or low-reflectivity targets. This study proposes a frequency modulation (FM) approach, FM-SMI, to enhance the capabilities of SMI setups. By intentionally modulating the laser frequency of 20 kHz, the FM-SMI technique induces a segmentation of the interference signal, effectively increasing the temporal resolution and facilitating the detection of finer vibration details. Comprehensive experiments involving oscillating speakers and rotating silicon wafers validate the superior performance of the FM-SMI system. Notably, the frequency-modulated signals exhibit stability and robustness, even under low-amplitude vibration conditions or when targeting low-reflectivity surfaces. The enhanced signal quality, coupled with numerical processing techniques, enables precise extraction of vibration characteristics, including amplitude variations and surface topographies. The proposed FM-SMI approach demonstrates its potential as a versatile tool for high-precision, non-contact vibration measurements across diverse applications, such as, non-destructive testing and the characterization of vibration induced by the rotational systems.