相位敏感光时域反射计(φ-OTDR)中使用相干性较好的窄线宽光源,因传感光纤中光脉冲产生的散射光发生干涉,故可利用干涉光的变化检测外界扰动,检测灵敏度较高。但传统的幅度检测φ-OTDR的结果难以实现定量检测,需要进行相位解调。基于3×3迈克耳孙干涉仪的相位解调系统是一种较好的解调方案,但直接解调的结果存在空间分辨能力小于传统幅度检测φ-OTDR的问题。采用四路检测方法来保持φ-OTDR的空间分辨能力,只需在系统结构中增加一路检测。同时考虑到窄线宽光源产生的脉冲内干涉对解调造成的不利影响,在提出四路检测相位解调φ-OTDR的基础上,从瑞利后向散射光的角度对基于3×3迈克耳孙干涉仪的相位解调φ-OTDR进行分析,并通过实验进行验证。完成了对5 km传感光纤上扰动信号的定量检测,检测线性度为0.9956,解调相位的幅度达到31.85 rad,解调系统的空间分辨率与传统的幅度检测φ-OTDR相同。

Phase-sensitive optical time domain reflectometry (φ-OTDR) uses narrow line-width laser with high coherence. In the sensing fiber, scattered lights from optical pulse interfere, and the interference light is highly sensitive to external disturbance. But the traditional amplitude-detection φ-OTDR is not quantitative detection, so that phase demodulation is necessary. Phase demodulation system based on 3×3 Michelson interferometer is cost-effective, but is of lower spatial resolution than the traditional amplitude-detection φ-OTDR. We propose a four-channel detection method to preserve the same spatial resolution as amplitude-detection φ-OTDR by adding only one detection channel. But the interference of scattered lights may have critical influence to phase demodulation. A four-channel detection system of phase demodulation φ-OTDR is analyzed based on 3×3 Michelson interferometer, from the aspect of Rayleigh backscattering light. The experiment shows that the disturbance around the fiber is detected quantitatively, with a linearity of 0.9956, phase sensing range of 31.85 rad, and the spatial resolution is same as that of amplitude-demodulation φ-OTDR.