A Broadband Distributed Vibration Sensing System Assisted by a Distributed Feedback Interferometer

A distributed vibration-sensing system based on phase-sensitive optical time-domain reflectometry (Phi-OTDR) and distributed feedback interferometer (DFI) with broad-band frequency response and high spatial resolution has been proposed and demonstrated. A couple of narrow line-width lasers with different wavelengths were used to form the light source, which were consistent with two channels of dense wavelength division multiplexer. Both functions of Phi-OTDR and DFI could work synchronously without influence between each other. The characteristic of broadband frequency disturbance event could be fully captured and identified by the DFI, while the corresponding location could be determined by the Phi-OTDR scheme. Unlike ordinary interferometer, the proposed DFI scheme could make single-end monitoring without the installation of extra accessories. Furthermore, broadband frequency response range and precise locating of the disturbance event could be achieved at the same time. Experimental results have shown that spatial resolution of 10 m and frequency response up to 1 MHz have been obtained over 2.16-km-sensing fiber, which have proved the validity of the proposed method.