Distributed fiber sensing system with wide frequency response and accurate location

Abstract

A distributed fiber sensing system merging Mach–Zehnder interferometer and phase-sensitive optical time domain reflectometer (Φ-OTDR) is demonstrated for vibration measurement, which requires wide frequency response and accurate location. Two narrow line-width lasers with delicately different wavelengths are used to constitute the interferometer and reflectometer respectively. A narrow band Fiber Bragg Grating is responsible for separating the two wavelengths. In addition, heterodyne detection is applied to maintain the signal to noise rate of the locating signal. Experiment results show that the novel system has a wide frequency from 1Hz to 50MHz, limited by the sample frequency of data acquisition card, and a spatial resolution of 20m, according to 200ns pulse width, along 2.5km fiber link.