Coherent OTDR Based Ultra-High Sensitive Acoustic Sensor Assisted with Distributed Microstructured Optical Fiber(DMOF) and Hollow Cylinder Transducer

An ultra-high sensitive distributed microstructured optical fiber (DMOF) acoustic sensor based on coherent OTDR demodulation method and hollow cylinder transducer is presented. As a consecutive longitudinal microstructured optical fiber, the DMOF contains backscattering enhanced points which greatly improved the signal to noise ratio(SNR) of the acoustic sensing signal. Based on coherent OTDR demodulation method, the amount of phase change caused by sound pressure can be directly obtained. In order to increase the phase sensitivity, sensing fiber between two backscattering enhanced points along the DMOF is wrapped on a hollow cylinder transducer as an acoustic sensing unit. Finally, experiments on detecting sound waves in air are carried out. The results demonstrate that our fiber acoustic sensor has a flat sensitivity frequency response from 500Hz to 5kHz with a phase sensitivity of around -112dB(re rad/μPa) and a peak sensitivity of -83.7dB at 80Hz. It is noteworthy that the sensing mechanism based on the DMOF can be further extended to distributed acoustic sensing.