Hengying Xu

Joint tracking and equalization scheme for multi-polarization effects in coherent optical communication systems

We propose a joint multi-polarization-effect tracking and equalization method based on two extended Kalman filters, which can cope with state of polarization (SOP) tracing, polarization demultiplexing, equalization for polarization dependent loss (PDL) and polarization mode dispersion (PMD) in PDM-M-QAM coherent optical communication system. The mathematical model of the proposed method is given and analyzed in detail. Through simulation, the proposed method is proved to be very effective in a 28 Gbaud/s PDM-16QAM system. With the proposed method, SOP tracing speed is up to 110 Mrad/s for azimuth angle and 1200 krad/s for phase angle, respectively, and PDL and PMD can be equalized simultaneously in the values of 10 dB and more than half of the symbol period.

Intelligent Bandwidth-Estimation Technique for Orthogonal Frequency Division Multiplexing-Based Elastic Optical Networking

Abstract—In orthogonal frequency division multiplexing (OFDM)-based elastic optical networking (EON), it is imperative to identify the parameters of the unknown OFDM signal intelligently, quickly, and robustly. Among these parameters, the bandwidth should be the first to be identified for the reason that other useful parameters such as number of subcarriers, baud rate, and frequency spacing can be obtained subsequently. In this paper we propose, for the first time to our knowledge, an intelligent bandwidth-identification technique for OFDM-based EON. The proposed technique can be divided into three sub-stages: estimation of power spectrum density, noise filtering based on empirical mode decomposition, and bandwidth identification based on a sliding window. When the number of samples is fixed at 215 and the optical signal-to-noise rate varies from 15 to 25 dB, the simulation results demonstrate that a bandwidth range from 2 to 40 GHz can all be successfully recognized with a minimum resolution of 39.1 MHz, and the average estimation absolute accuracies (EAAs) exceed 95%. Moreover, the technique has a good tolerance to chromatic dispersion and is independent of the number of subcarriers and frequency offsets. Finally, we verify the effectiveness of this technique by an experiment involving a 7.04 Gbps OFDMbased EON with minimum EAA of 94.12%, in which its bandwidth can be successfully recognized.

Window-split structured frequency domain Kalman equalization scheme for large PMD and ultra-fast RSOP in an optical coherent PDM-QPSK system

A window-split frequency domain Kalman scheme is proposed in this paper for the equalization of large polarization mode dispersion (PMD) and ultra-fast rotation of state-of-polarization (RSOP) which is an extreme environment due to the Kerr effect and the Faraday effect under the lightning strike near the fiber cables. In order to carry out the proposed Kalman scheme, we give a simplified and equivalent fiber channel model as a replacement for the general model of the polarization effect of the co-existence of PMD and RSOP. With this fiber channel model, we can conduct compensation for PMD in the frequency domain and tracking RSOP in time domain. A half analytical and half empirical theory for the initialization of the process and measurement noise covariance is also presented in theory and verified by the numerical simulation. The performance of the proposed Kalman scheme is checked in the 28Gbaud PDM-QPSK coherent system built on both simulation and experiment platforms. The simulation and experiment results confirm that compared with the generally used constant modulus algorithm (CMA), the proposed scheme provides excellent performance and stability to cope with large range DGD from 20ps to 200ps and RSOP from 200krad/s to 2Mrad/s, with less computational complexity.

Joint tracking and mitigation of linear dynamic impairments using a 3-stage extended Kalman filter in fiber channel

We propose a novel joint tracking and mitigation scheme for linear dynamic impairments using a 3-stage extended Kalman filter. Simulation results show that it can quickly track and compensate the impairments including multi-polarization effects, frequency offset and phase noise.