Distributed Fiber Optic In-Line Intrusion Sensor System

A novel fiber optic in-line distributed sensor system for location of an intrusion is proposed. A 3 dB coupler and a Faraday rotation mirror (FRM) are employed to form an interferometer. There are two light paths that have the same optical length but travel different sequence paths in the interferometer. These two paths pass through the intrusion point at different time, so the phase difference is existent. After interference, a fast Fourier transform (FFT) is applied on the output signal to obtain the phase angle in the double intrusion frequency. And then the position of the intrusion point can be determined. Simulation results show that this fiber optic in-line distributed sensor system can locate the intrusion point at a distance of 40 km, with the deviation no more than 130 m, and the relative error is 0.32%.