A Low-Noise Fiber Phase-Sensitive Optical Time-Domain Reflectometer for Seismology Application

A fiber phase-sensitive optical time-domain reflectometer (a distributed acoustic sensor) with a low-noise output signal in the frequency range of 0.01-1 Hz is proposed for seismology applications. The sensor architecture is based on an unbalanced Mach-Zehnder interferometer, which is used to form a dual-pulse probe signal with required phases of its components and to stabilize the frequency of the laser source in the feedback circuit. The low noise level of the output signal is achieved in the proposed circuit by compensating for the difference in the optical paths of the dual-pulse probe signal fields scattered by different fiber sections. The applicability of the proposed circuit has been experimentally demonstrated by detecting a remote earthquake using a fiber-optic cable located at the bottom of the Black Sea.