Joint Equalization of RSOP and PMD Impairments Based on Square-root Cubature Kalman Filter for PDM-16QAM System

In this paper, a polarization demultiplexing scheme based on Square-root cubature Kalman filter (SCKF) is proposed, which can compensate polarization mode dispersion in the frequency domain and track the rotation of state of polarization (RSOP) in the time domain. The performance of the SCKF scheme has verified by 28 GBaud PDM-16QAM system. The simulation results demonstrate that the proposed scheme can handle ultra-fast RSOP up to 55 Mrad/s, and still has a compensation capability of about 90 ps for different group delay (DGD) under the extreme RSOP variation of 15 Mrad/s. It achieves a higher performance than the conventional Extended Kalman filter (EKF) and has a higher OSNR tolerance of about 1dB. The time complexity of SCKF is O(NlogN).

I. Introduction

In recent years, with the explosive growth of traffic brought by virtual reality, video-on-demand and mobile internet, the capacity demand for coherent optical communication system is increasing sharply. As an important technology to double the fiber transmission capacity, PDM utilizes two orthogonal polarization states (SOPs) of lightwave to transmit information simultaneously. Nevertheless, PDM system is more sensitive to the polarizing effects during fiber transmission, which include polarization mode dispersion (PMD), rotation of state of polarization (RSOP), polarizing related loss (PDL), etc. In the actual optical fiber communication system, the extreme conditions of lightning strike in summer will cause the RSOP of up to 5.1 Mrad/s in the optical ground wire (OPGW) As we all know, the RSOP direction is consistent with the slow principal state of polarization of PMD[1]. The traditional constant modulus algorithm (CMA) or multi-mode algorithm (MMA) based on the multiple input multiple output (MIMO) structure is invalid for the joint effect of this fast RSOP and PMD, accordingly effective polarization demultiplexing cannot be achieved.