Multi-wavelength coherent vibration sensing using a mode-locked laser diode

We propose and experimentally demonstrate a multi-wavelength differential coherent vibration (MDCV) measurement scheme using a monolithically integrated Fabry-Pérot mode-locked laser diode (FP-MLLD). The scheme leverages multiple mutually coherent laser modes generated from a single FP-MLLD to form multiple probing pairs, enabling multi-channel coherent detection. In the time domain, the probing and reference signals exhibit a short-pulse waveform, which delivers higher peak power and signal-to-noise ratio (SNR) compared to continuous-wave or dual-wavelength sine-wave schemes. Experimental results show that the proposed system achieves vibration frequency measurement over a range of 5 Hz to 800 Hz with an SNR of ∼20 dB. Multi-channel measurement capability is validated via three spectrally filtered wavelength channels, all of which accurately resolve the target vibration frequency. This scheme features a simplified architecture, low cost, and native multi-channel capability, showing potential for multi-target or multi-directional vibration measurement applications.