Rayleigh-Adaptive Phase Gating for Interference-Fading Elimination in Phase-Conjugated Go-code optimized φ-OTDR

Interference fading is a significant challenge faced by φ-OTDRs, which reduces signal clarity and sensitivity and hinders accurate event detection and localization along the fiber. To address this issue, we propose Rayleigh-Adaptive Phase Gating (RAPGate) with phase-conjugated Go-code, a novel technique that employs the Rayleigh backscattering decay profile to dynamically optimize interference fading elimination. RAPGate employs amplitude-gated selection between phase-conjugated probe pulse pairs, using a distance-adaptive threshold Th(z, t) that automatically adjusts to local signal characteristics along the fiber. Experimental validation over a 20-km fiber under test demonstrates that RAPGate effectively eliminates interference fading with substantial reduction in signal dropouts and improved measurement reliability while maintaining the original 10-m spatial resolution.