Sagnac vibration sensing system with nested pulse method

A novel vibration location method with nested pulses for distributed optical fiber vibration sensing system is proposed. The interferometric structure for vibration detection and location with nested pulse method is firstly designed. The continuous-wave light is modulated into a series of periodic nested pulses in the linear Sagnac interferometer. Each nested pulse contains a certain number of sub pulses to locate the position of vibration signal with the help of envelope derivation and threshold judgment. Experimental results show the location feasibility for vibration signals at different positions of long-range optical fiber, with the positioning error of 10m at 0.5 km and the positioning error of 26 m at 45.314 km. This method provides one solution for the location of actual vibration without the limit of frequency band.