A Fading-Discrimination Method for Distributed Vibration Sensor Using Coherent Detection of $\varphi $ -OTDR

We have proposed an effective method to discriminate the false alarm peaks induced by fading effect in distributed fiber-optic vibration sensing systems based on coherent heterodyne detection of phase-sensitive optical time-domain reflectometer (φ-OTDR). By comparison of the demodulated phase of backscattered light returned from the location of the sensing fiber before and behind the alarm peaks, the false alarm peaks can be distinguished from real vibration alarm peaks. We have demonstrated a fiber-optic distributed vibration sensor with efficient fading discrimination based on φ-OTDR system that has a measurement range of 2.5 km, a spatial resolution of 2.5 m, and a signal-to-noise ratio of 16 dB. The results provide a simple and low-cost approach for the false alarm discrimination in all-fiber φ-OTDR systems.