Suppression of interference fading in φ-OTDR based on spectrum extraction and phase-shift transform

In phase-sensitive optical time domain reflectometer (φ-OTDR), interference fading may result in the intensity of Rayleigh backward scattering (RBS) signals approaching zero at the fading positions, submerging them in noise and leading to abnormal demodulation of vibration signals. To mitigate the impact of interference fading on vibration detection, a scheme combining spectrum extraction (SE) with phase-shift transform (PST) is proposed. This scheme first performs SE on the beating signals, followed by PST of each frequency component, ultimately resulting in multiple mutually independent signals. By aggregating these signals through Rotated-vector-sum (RVS) method, interference fading can be suppressed and the vibration-induced phase changes can be precisely recovered. Experimental results demonstrate a reduction in the proportion of spatial points affected by fading from 3.46% to 0.0107%.