Laser and Nonlinear Phase Noise Tracking and Estimation in Long Haul 400 Gbps Single Carrier PDM-16-QAM Systems using Multi-step Kalman Filter

Coherent optical communication system performance is often limited by LPN (laser phase noise) and NLPN (nonlinear phase noise). A n-step Kalman filter to track and estimate LPN and NLPN is proposed for 400 Gbps PDM-16-QAM coherent optical system. Simulations show that for 100 kHz laser linewidth, reducing the sampling factor of filter by 10, Q-factor of 14.5 dB can be achieved over 1200 km transmission and $\lt 1\mathrm{d}\mathrm{B}$ degradation is observed for n=20. Q-factor curves indicate that multi-step Kalman filter (MKF) performs better than linear step Kalman filter. MKF with $m=10$ can successfully mitigate the LPN and NLPN for the proposed system with maximum laser linewidth tolerance upto 1 MHz over $40\times 80$ km. Results show that MKF can optimally track carrier phase noise and Kerr nonlinearities, thereby validating our proposed filter design.