Vibration Detection Based on Multipath Information Fusion in Dual-Channel ϕ-OTDR System

Single-path intensity-demodulated phase-sensitive optical time-domain reflectometer (φ-OTDR) is susceptible to noises and random interferences, which increases the probability of missing detection of external vibrations. In the work, a dual-channel φ-OTDR is experimentally investigated to detect pencil-break vibrations and to locate a running vehicle on a highway. For the two experiments, the double sensing channels are respective the LP
₀₁
and LP
₁₁
modes of a two-mode step-index fiber and two independent standard single-mode optical fibers extracted from an armored four-core cable. The Rayleigh scattering traces from the two channels are both collected and processed by the conventional differential accumulation algorithm (DAA) and standard deviation algorithm (SVA), respectively. Furthermore, a decision signal is proposed via fusing the accumulated differential signals by the DAA and the variances of the Rayleigh traces by the SVA, by which we are able to conclude whether there is a vibration signal over the sensing link. Experimental results demonstrate that our method is able to identify the vibrations caused by pencil breaks and moving vehicles, respectively, with a considerable improved reliability compared to the widely used DAA.