空间差分干涉的光纤分布式水下声波测量

为了实现大范围的水下微弱声波探测,提出了一种基于后向瑞利散射空间差分干涉的光纤分布式声波检测(DAS)技术。声波振动引起单模传感光纤中后向瑞利散射光的变化,将含有声波信息的后向瑞利散射光注入到非平衡迈克尔逊干涉仪,调节干涉仪的臂长差实现不同长度的相邻空间段的后向瑞利散射光干涉,然后采用3×3耦合器解调技术解调出相位信息,实现声波信号的测量。实验搭建了一套基于DAS技术的水下声波测量系统,该系统不仅能够实时准确定位两个声波位置,还能还原声波的幅值、频率、相位等信息,并且实现了1kHz情况下的-148.8dB(re rad/μPa)水下声压相位灵敏度,100~1 500Hz频率的频响平坦度在1.2dB之内。实验结果证实DAS技术能够实时快速地实现多个声波信息的定量测量。

Measurement of underwater acoustic wave using optical distributed acoustic sensing based on space difference

To detect weak underwater acoustic signal over large areas ,an optical Distributed Acoustic Sensing(DAS) scheme based on space difference of Rayleigh backscattering was presented .In this scheme ,Rayleigh backscattered light with phase changes induced by the acoustic signal along a single-mode sensing fiber was split and fed into an imbalanced Michelson interferometer .Adjusting the path difference of the imbalanced Michelson interferometer ,the Rayleigh backscattered light interference of different lengths of adjacent space segments along the sensing fiber was realized .Subsequently ,the phase information including the acoustic signal was demodulated by the 3 × 3 coupler demodulation technology .An underwater acoustic wave measuring system based on DAS was implemented ,which can not only locate the two acoustic positions accurately in real time ,but also restore the amplitude ,frequency and phase of sound waves .In addition ,the acoustic phase sensitivity is -148 .8 dB (re rad/μPa) at 1 kHz ,and the frequency response flatness at frequencies ranging from 100 Hz to 1500 Hz is within 1 .2 dB .The experimental results confirm that the novel Φ-OTDR technology can enable quantitative measurements of multiple acoustic information in real time .