Performance enhancement of phase-demodulation ϕ-OTDR using improved two-path DCM algorithm

Abstract Dynamic phase demodulation techniques based on phase-sensitive optical time-domain reflectometry ( ϕ -OTDR), including passive 3 × 3 coupler demodulation, offer significant potential in applications involving acoustic sensing and imaging. However, the main challenge to overcome in a ϕ -OTDR system based on a 3 × 3 coupler including eliminating the effect of the three output signals of the 3 × 3 coupler that cannot achieve 120° phase difference. And also, to implement such a system, three high-sensitivity photo-detectors are required to work synchronously. Unlike previous ϕ -OTDR systems based on 3 × 3 coupler, the system proposed herein only needs two photo-detectors, which reduces system hardware costs. In the signal-processing section, we use the improved two-path differential cross-multiplication algorithm to minimize impact of incomplete symmetry of the 3 × 3 coupler. Theoretical analysis, simulation and experimental results show that the proposed structure and algorithm improve the stability and antinoise demodulation of system. Experimental verification shows that the proposed system correctly recovers the actual waveforms of different vibration events occurring simultaneously at multiple positions. The background noise of the proposed ϕ -OTDR system is about − 30 . 95  dB, as well as a detection frequency range from 50 Hz to 10 kHz. This system should provide a new option for dynamic acoustic measurements.