Unidirectional Ultra-Long Distributed Optical Fiber Sensor

In this paper, we propose and experimentally demonstrate an ultra-long distributed fiber vibration sensing system using unidirectional forward transmission of a continuous-wave signal coherent detection with digital processing. Two optical fibers, which are close to each other, deployed for sensing. A loop-back configuration is formed by splicing these two fibers at the far end fibers. The location event identified analyzing null points in frequency spectrum extracted phase signal. Thanks nature transmission, Rayleigh backscattering noise can be avoided. Meanwhile, enables amplifiers compensate loss hence fundamentally overcome range limit. We successfully localization single point multi-point vibrations measurement errors less than ±100 m ±200 m, respectively, over 500-km range. proposed scheme opens new possibilities haul applications.