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

• A φ-OTDR combined with a MZI is proposed for lower nuisance alarm rate.
• φ-OTDR detects and locates the disturbance and MZI verifies the real disturbance.
• NAR is efficiently reduced to ∼1% from ∼15% with probability of detection of ∼97%.
• The dependence of NAR on the pulse width and sampling rate is investigated.
• This work is low cost, of simple configuration and without complicated algorithm.

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 1 μs and sampling rate vary in the range from 10 to 50 MS/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.