Suppression of Interference Fading by VID for φ-OTDR

The use of highly coherent light sources in phase-sensitive optical time-domain reflectometry (φ-OTDR) inevitably introduces interference fading, which severely degrades the performance of event detection. To address this issue, we propose an improved interference suppression method termed VID, which integrates variational mode decomposition (VMD), interferometric spatial phase-shift (ISP), and dual-rotating vector summation (DRVS). The VID first employs VMD to extract weakly correlated intrinsic mode functions (IMFs) from the beat signal, thereby overcoming the high spectral correlation inherent in conventional frequency-division schemes. Subsequently, ISP achieves rapid phase demodulation without introducing latency, and DRVS suppresses fading by combining phase-corrected vectors across time and frequency domains. Comparative experiments between VID and the conventional spectrum extraction and remix (SERM) demonstrate that VID exhibits an improved performance in interference fading suppression. This improvement is attributed to the fact that SERM suffers from high correlation among its multi-spectral components, which limits its suppression capability. Conversely, VID achieves remarkable lower inter-modal correlation, leading to a greater reduction in both the density of interference fading points and the phase jump rate.