Digital phase shift based simulated coherence phase demodulation technology for [formula omitted]-OTDR

Abstract

In this paper, we propose a digital phase demodulation scheme for phase-sensitive optical time-domain reflectometer (Φ-OTDR) systems based on simulated coherence for digital phase shift, in which three-path signals with a phase interval of 120° can be obtained by employing digital simulated orthogonal coherence for phase shift instead of using a hardware 3×3 coupler and three detectors, while the high-frequency component can be eliminated through cross differential between simulated coherence signals. On this basis, the phase variation of Rayleigh backscattering (RBS) light can be analyzed by differential cross multiplication (DCM). The performance of the proposed scheme is evaluated through experiments by detecting a series of vibration signals with various sensing distances, vibration frequencies, and waveforms. The experimental results demonstrate that the phase variation caused by external vibration can be effectively reconstructed and a strain resolution of 0.5 nɛ and the SNR of 51.03 dB can be achieved through the proposed demodulation method, which significantly simplifies the system and effectively suppresses the deviation of phase interval and noise caused by hardware demodulation.