Measuring displacement based on spectral decay in multiple laser self-mixing interference

Addressing the demand for micro-displacement measurement in fields like precision engineering and biosensing, this paper proposes a dynamic measurement method based on multiple laser self-mixing interference (MSMI). To overcome traditional system limitations, we constructed a three-mirror cavity feedback structure that utilizes multiple reflections to generate multiplicated interference fringes. The waveform was converted to the power spectrum using the Fourier transform. By extracting the decay coefficient of the spectral line, we established a quantitative relationship with displacement. This effectively avoids traditional time-domain fringe counting issues, such as inherent resolution limits and cumulative phase errors. Utilizing a stable 532 nm laser, the proposed system achieved a relative error of less than 1.8 % and a sensitivity of 0.1 nm/Hz over a displacement range of 1064 nm to 5365.22 nm. Furthermore, repeatability tests confirm the system’s inherent robustness against environmental disturbances and excellent measurement repeatability. This structurally simple and highly sensitive method provides an effective approach for advanced micro-displacement measurement applications.