Weak Coupling Point Detection in Distributed Polarization Coupling Measurement Based on Variational Mode Decomposition

Distributed polarization coupling measurement can be used to detect coupling points (CPs) in polarization-maintaining fibers (PMFs). Owing to the imperfection of the PMF structure and external weak disturbance, weak CPs are produced. However, weak CPs are easily submerged in background noise, so they are difficult to detect. In this article, we propose a method based on variational mode decomposition (VMD) to detect weak CPs. Using VMD and empirical mode decomposition (EMD), a comparison is made to evaluate the performance of extracting weak CPs in interferograms. As the VMD approach is embedded with the Wiener filter, it exhibits robustness to noise, which outperforms EMD in extracting weak CPs for both simulated and experimental interferograms. The noise level and mechanical scanning vibration frequency reduce the reconstruction accuracy of CPs. Moreover, the effects of mode number and bandwidth on decomposed results in the VMD method are discussed in detail. Additionally, the VMD-based method can be used to process other optical signals.