title: Improved two-stage equalization for coherent Pol-Mux QPSK and 16-QAM systems.
abstract: We report a two-stage blind frequency domain equalization method for long-haul coherent polarization-multiplexed (pol-mux) systems using quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (16-QAM). In the first stage, blind CD parameter prediction is conducted prior to a CD equalizer. This supports flexible path switching in optical networks. In the second stage, a frequency-domain multi-modulus algorithm (MMA) equalizer is used to cope with the residual fiber impairments and perform polarization de-multiplexing. Compared with the conventional constant modulus algorithm (CMA), MMA shows advantages including better steady state performance and a faster convergence rate. Furthermore, all the estimation and equalization algorithms are implemented in the frequency domain which potentially provides the least complexity for the pol-mux optical coherent systems. The proposed algorithm is experimentally demonstrated with an 800-km 10 Gbaud coherent optical pol-mux system. For QPSK signal, the proposed method achieves error-free transmission and shows superior convergence speed against CMA, and for 16-QAM signals, the proposed MMA outperforms CMA with more than 1-dB improvement in Q-value.
authors.affiliation: Victoria Research Laboratory, NICTA Ltd, Level 2, Building 193, Electrical and Electronic Engineering, University of Melbourne, Australia. zhuc@student.unimelb.edu.au
authors.forename: Chen
authors.initials: C
authors.lastname: Zhu
authors.forename: An V
authors.initials: AV
authors.lastname: Tran
authors.forename: Simin
authors.initials: S
authors.lastname: Chen
authors.forename: Liang B
authors.initials: LB
authors.lastname: Du
authors.forename: Trevor
authors.initials: T
authors.lastname: Anderson
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Lowery
authors.forename: Efstratios
authors.initials: E
authors.lastname: Skafidas