Experimental investigation on lower nuisance alarm rate phase-sensitive OTDR using the combination of a Mach–Zehnder interferometer

Abstract

Phase-sensitive optical time domain reflectometer (φ-OTDR) currently suffers from high nuisance alarm rate (NAR) due to fluctuation of scattering light intensity, nonlinear coherent addition, and ambient noises in complicated noisy environments. In order to lower NAR, a φ-OTDR combined with a Mach–Zehnder interferometer (MZI) is proposed and experimentally demonstrated. In this system, φ-OTDR takes the role of detecting and locating the disturbance and MZI verifies the real disturbance by using an alarm threshold. Experimental results demonstrate that NAR of φ-OTDR with MZI can be efficiently reduced to ∼1% from ∼15% of a single φ-OTDR and a high probability of detection of ∼97% is achieved. Furthermore, the dependences of NAR and probability of detection on the pulse width and sampling rate is investigated. When the pulse width is changed from 0.1 to 1μs and sampling rate vary in the range from 10 to 50MS/s, NAR and probability of detection only exist a little fluctuation. The proposed scheme is helpful to reduce NAR of the current single φ-OTDR without introduction of complicated algorithm and also have simple configuration with low cost.