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

We demonstrate fully blind processing and reduced-complexity 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 at a bit error rate of 2.7 × 10^-2. The equalization of linear polarization-dependent effects is performed by a radius-directed constant modulus algorithm (RD-CMA), enabled by a multiradii training stage, yielding a very small penalty (<;0.1 dB in terms of Q² factor) relatively to data-aided 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 split-step 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.