High-Frequency Vibration Detection of Phase-Sensitive Optical Time-Domain Reflectometer

The phase-sensitive optical time-domain reflectometer (phi-OTDR) can effectively detect the vibration information of fiber; however, the detectable vibration frequency range is generally between several hundred hertz and several kilohertz, limited by the length of the sensing fiber. To improve the vibration detection range, a phi-OTDR system that uses heterodyne coherent detection is built in this study. The phase information of the scattered optical signal of the sensing fiber is obtained using the I/Q demodulation method. Differential phase demodulation in the space and time domains is consecutively performed to achieve a distributed detection of high frequency vibration signals in the fiber. Furthermore, the feasibility of the proposed high-frequency vibration detection scheme is theoretically analyzed, and the vibration signal with a frequency of 500 kHz is effectively demodulated in the experiment, obtaining a sensing distance of 23 km.