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Fully Blind Linear and Nonlinear Equalization for 100G PM-64QAM Optical Systems

Guiomar, F. P. ; Amado, S. B. ; Carena, A. Carena ; Bosco, G. B. ; Nespola, A. N. ; Teixeira, A. ; Pinto, A. N.

IEEE/OSA Journal of Lightwave Technology Vol. 33, Nº 7, pp. 1265 - 1274, April, 2015.

ISSN (print): 0733-8724
ISSN (online): 0733-8724

Journal Impact Factor: 2,567 (in 2015)

Digital Object Identifier: 10.1109/JLT.2014.2386653

We demonstrate fully-blind processing and reducedcomplexity nonlinear equalization (NLE) of a 100G PM-64QAM optical channel in a 50 GHz WDM grid, achieving a maximum reach of 1524 km over pure silica core fiber (PSCF) at a bit error rate (BER) of 2.7x10^-2. The equalization of linear polarizationdependent effects is performed by a radius-directed constant modulus algorithm (RD-CMA), enabled by a multi-radii training stage, yielding a very small penalty (<0.1 dB in terms of Q^2 factor) relatively to data-aided CMA (DA-CMA). Applying a simplified Volterra series nonlinear equalizer (simVSNE), operating in the frequency-domain, we demonstrate a reach extension of 27% relatively to linear equalization. Due to its lower spatial resolution requirements, the simVSNE technique is shown to provide a more efficient NLE than the well-known back-propagation splitstep Fourier method, both in terms of latency and number of complex multiplications per sample. The potential benefit of NLE for fully-blind processing of high-order QAM optical signals is demonstrated by an incremental reduction of the RD-CMA penalty to <0.04 dB.