Fully Blind Nonlinear Equalization for Optical Systems

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 2:7102. 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 Q2 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.