Characterization of Mode Coupling in a Few-Mode Fiber Based on Optical Frequency Domain Reflectometry

An effective technique based on optical frequency domain reflectometry (OFDR) for analyzing mode coupling events in a few-mode fiber (FMF) is proposed. Its feasibility is demonstrated both theoretically and experimentally on a two-mode fiber. We elaborate on the process to establish the correlation between mode coupling strength and amplitude of cross correlation peak by analyzing Rayleigh scattering fingerprint spectra and correlation algorithms. Concurrently, on account of group velocity difference between the two modes, the precise localization of the coupling point can be deduced from the group delay between scattered traces of the two modes, which permits the precise location of coupling events within a fiber link. In the experiments, we induced mode coupling between LP01 and LP11 modes in a two-mode fiber by means of applying transverse stress to the fiber under test and achieved good measurement results by employing the proposed method. Moreover, we initiated preliminary research on the location and strength analysis of plural coupling events. As an effective in situ monitoring technique for mode coupling, this methodology holds significant potential for applications, such as defect detection in FMFs and high-power laser chain mode coupling monitoring.