Interference fading suppression method for φ-OTDR based on time-distance dual-domain phase differential.

To mitigate interference fading induced by phase randomness in multi-beam interference in phase-sensitive optical time-domain reflectometry (φ-OTDR), we present a time-distance dual-domain phase differential method (TDPD) that reconstructs constructive interference conditions for complex optical wave vectors in fading regions. The TDPD approach suppresses noise-dominated fading through distance-domain vector superposition while eliminating vibration-induced fading via time-domain differential phase processing, which reduces inter-wave phase differences to the theoretical limit imposed by pulse repetition frequency. The temporal-neighboring phase unwrapping and integration strategy are employed to recover the original phase waveform prior to differential operations. Experimental validation on a 10 km fiber demonstrated accurate phase measurements for 10 Hz, chirp, and 0.1 Hz vibrations. TDPD simultaneously addresses fading in both noise- and vibration-affected regions, achieving >40 dB SNR improvement in vibration regions compared to conventional methods. This cost-effective framework with high computational efficiency offers a reliable solution for precise phase demodulation in φ-OTDR systems.