Research On Polarization-Related Damage Estimation And Compensation Algorithms For Coherent Optical Transmission Systems

With the rapid growth of various emerging network services,polarization multiplexing combined with coherent detection of highcapacity and high-spectral-efficiency optical transmission systems continue to evolve rapidly toward higher speed,higher capacity and longer distances,while more complex polarization-related damage has become one of the key factors limiting system performance.During long-distance transmission,the signal has a higher probability of being affected by the fast rotation of state of polarization(RSOP)caused by lightning and other extreme weather,and the accumulation of large polarization mode dispersion(PMD)in the fiber channel for long-distance transmission makes it difficult for existing algorithms to achieve fast-varying RSOP tracking under large PMD.In addition,the existing differential group delay(DGD)estimation algorithm has the problem of low estimation accuracy.In this paper,we focus on the problems of polarization-related damage estimation and compensation in polarization multiplexing coherent optical transmission systems,and the main research work and results are summarized as follows.1、A broadband PMD damage model based on time function is studied and validated to address the problem that the existing PMD model is difficult to accurately characterize the complex variation of PMD in high-speed broadband polarization division multiplexing(PDM)coherent optical systems.The system simulation results show that the model can characterize all the polarization states of the high-speed transmission system and the DGD distribution satisfies the theoretical probability analysis.40GBaud Nyquist PDM-QPSK system off-line experimental results show that the model is similar to the cumulative PMD impairment effect in the actual long-distance transmission fiber channel and can reasonably characterize the PMD impairment of the high-speed broadband channel.2、A multi-symbol Extended Kalman Filter(EKF)based RSOP tracking algorithm is proposed to address the problem that the existing RSOP tracking algorithm is difficult to work stably and reliably under large PMD damage conditions.Simulation results of the 28GBaud Nyquist PDM-16QAM system show that the proposed algorithm can tolerate PMD of 14ps at RSOP up to 9Mrad/s,which is twice as tolerant as the conventional two-stage EKF algorithm.Simulation results of the 28/42/56GBaud Nyquist PDM-16QAM system show that the proposed algorithm tolerates PMD in the range of 18/10/6.25ps,respectively.3、To address the problem of low estimation accuracy of existing DGD estimation algorithms,a DGD estimation algorithm based on const amplitude zero auto-correlation(CAZAC)sequence is proposed.simulation results of the 40GBaud Nyquist PDM-QPSK/16QAM system show that the algorithm The simulation results of the 40GBaud Nyquist PDM-QPSK/16QAM system show that the algorithm can maintain the estimation error less than 3ps in the 70ps DGD range.40GBaud Nyquist PDM-QPSK/16QAM offline experimental system verifies that the DGD estimation error in the 60ps range is about 4ps.