Sensitivity enhancement of distributed strain sensing system combined Φ-OTDR with ultraweak FBG array

A high-sensitivity FBG strain sensing system based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) and coherent detection technology was proposed. By employing an ultra-weak FBG array, the Rayleigh backscattered light is enhanced, and its amplitude and phase information are extracted using I/Q demodulation. Experimental results demonstrate that the system accurately locates strain positions and demodulates phase variations induced by strain. When using FBG as the sensing head, the strain sensitivity reaches 0.01062 rad/nε, which significantly outperforms traditional single-mode fiber. This makes the system well-suited for high-precision structural health monitoring (SHM) applications.