Using fiber optic sensors to monitoring the vibration in subway tunnel

This paper proposes a novel time-division locking technique for improving the consistency and stability of fiber optic interferometric seismometers. The analysis of factors affecting system consistency and stability are given in details. The principle of the time-division locking technique is highlighted. Test results show that the system noise level is 12.6 ng/(√Hz) @ 5 Hz, the noise level differences between every two channels are less than 2.6 dB, the noise level fluctuations of all channels are less than 1.4 dB over 24 hours.