Abstract: A displacement measurement system based on a single mode fiber and a coupler is proposed. The two arms of the output end of the coupler are connected with a collimating lens to form a differential structure when irradiated to both sides of the measured object. The displacement resolution of the system is improved by two times, the resolution can reach a quarter of the wavelength, and the whole system is less disturbed by temperature. Through simulation analysis and experimental verification, the feasibility of this method is proved. Multiple Hilbert transform method is used to carry out displacement reconstruction. The results show that the displacement reconstruction accuracy of this system is also better than that of single-channel system, and the reconstruction error is reduced from 111 nm to 60 nm.

Key words: fiber optic sensor, Fabry-Perot cavity, displacement measurement, differential, hilbert transform