Analysis and removal of the second-order ghost coupling points in distributed multiple coupling point measurements

Abstract

White light interferometry is used to measure distributed polarization coupling (DPC) in high-birefringence polarization-maintaining fibers (PMFs). Second-order ghost coupling points (CPs) exist in DPC measurements when there are multiple intrinsic CPs in PMFs, which degrade the measurement accuracy. Therefore, it is essential to analyze and remove the second-order ghost CPs. Based on Jones matrix analysis, the quantitative relationship between intrinsic CPs and second-order ghost CPs is such that when there are N intrinsic CPs, the number of second-order ghost CPs is . By fusion splicing a variable optical delay line (VODL) in a slow axis to separate the modes propagating along the fast axis and slow axis in the time domain, the second-order ghost CPs among intrinsic CPs can be removed, and the delay offset of the VODL depends on the position of the intrinsic CPs in the PMFs. When there are three intrinsic CPs, where one is induced by stress and the other two are induced by axis misalignment, experimental results agree with theoretical analysis. By appropriately setting the VODL delay offset, the method for removing second-order ghost CPs is effective, as proved by experimental results. Additionally, the method can be used to measure a Y wave guide and other polarization-sensitive optical devices.