A novel fiber optic ring-down interferometer for sensing

A ring-down interferometer (RDI) based on a modified Mach–Zehnder structure by incorporating a pair of mirrors with very high reflectivity into each of its two arms, respectively is proposed in this paper. Launching a coherent light pulse into the interferometer, in each arm, pulse ring-down occurs between its two mirrors and outputs a chain of pulses. The two chains of pulses from the two arms combine and interfere pulse by pulse at the detector and the difference of the light phase between the two arms will be enlarged linearly in proportion to the times of ring-down.