Monitoring PDL Value and Location Using DSP-Based Longitudinal Power Profile Estimation

In polarization-multiplexed digital coherent systems, polarization dependent loss (PDL) is a dominant factor limiting the capacity and distance of fiber-optic transmission systems. In this paper, we propose polarization-wise power profile estimation (PPE) based on a linear least squares algorithm to estimate the value and location of excessive PDLs. The method visualizes polarization-wise signal power profiles at a coherent receiver with high sensitivity. We also experimentally demonstrate that PPE can detect PDL in an optical multi-span transmission link using the method. The experiment was performed using dual-polarization transmission over a 3-span × 50-km link, with a PDL resolution of 1-3 dB and a spatial step size of 1 km. In high power conditions, all estimated PDL values agree with actual values with estimation errors of well below 0.5 dB.