相位敏感光时域反射计(φ-OTDR)可以有效地检测光纤的振动信息,但受传感光纤长度的限制,可检测的振动频率范围一般在几百赫兹到几千赫兹之间。为了提高振动检测范围,组建了基于外差相干检测的φ-OTDR系统,采用I/Q解调方法获得传感光纤散射光信号的相位信息,对此相位信息在空间域与时域上相继进行差分相位解调,从而实现对光纤中高频振动信号的分布式检测。理论上分析了高频振动检测方案的可行性,并在实验中有效解调出了频率为500 kHz的振动信号,传感距离达到了23 km。

The phase-sensitive optical time-domain reflectometer (φ-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 φ-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.