150 km Single-span Distributed Vibration Sensor based on Compensated Self-interference Forward Transmission

Undersea earthquakes can have a major impact on coastal cities, submarine infrastructure and environment. To provide advance warning and condition assessment, remote monitoring is critical. However, the current methods of undersea earthquake monitoring have some limitations, such as limited number of sensors, high deployment cost, severe signal attenuation, etc. In this study, we propose a new approach for super-long range vibration monitoring, by detecting vibration-induced phase change along a single sensing fiber using a double-ended forward-transmission distributed fiber-optic vibration sensing system with a compensated self-interference sensing mechanism. The experiment results show a single-span sensing range of 151.5 km without optical amplification, a spatial resolution of 10 m, and the position error can be as small as 37.6 m. The average sensitivity is ∼12.2 mrad/μϵ, and the average limit of detection is 186.7 pϵ/Hz1/2. The vibration frequency range tested is between 100-500 Hz. The sensing system has several advantages, such as super-long sensing distance, relatively low-coherence laser, anti-electromagnetic interference, etc. This study provides a new technical solution for undersea earthquake monitoring, which can improve the early warning and assessment capabilities of undersea earthquakes.