Fault detection of few-mode fiber based on high-order mode with high fault detection sensitivity

We report on the fusion splice loss characteristics of each mode in few-mode fiber (FMF). The fusion fault loss characteristics of all modes of the six-mode step-index and graded-index fibers are measured, respectively. The high-order modes with high fault detection sensitivity are presented. The fault events with different loss amplitudes can be accurately characterized by high-order modes. On this basis, a fault detection and location method for FMF based on backscattered light of high-order modes is proposed and experimentally demonstrated. Rayleigh backscattering light of high-order modes is utilized to detect the faults of 7.2 km six-mode step-index fiber with three fusion splice points with different fusion quality, the detection results of each mode are compared. The high-order modes LP_21a, LP_21b, and LP₀₂ with high fault detection sensitivity are shown, three fault points located around 1.03, 3.1, and 3.2 km of the FMF are successfully detected. While the LP₀₁, LP_11a, and LP_11b modes can detect only one fault point, which is located around 3.19 km of the FMF.