Post-compensation of nonlinear distortions of 64-QAM signals in a semiconductor based wavelength converter

We experimentally investigate post-compensation of nonlinear distortions induced by a wavelength converter (WC) based on four-wave mixing in a semiconductor optical amplifier. The technique exploits a low-complexity digital filter-based back-propagation (DFBP) method. We perform post-compensation of nonlinear distortions following single stage wavelength conversion of 5 Gbaud 64- quadrature amplitude modulation (QAM). We examine the DFBP performances in the presence of a degraded optical signal-to-noise ratio at the WC input and we explore the WC optimal operating conditions. Also, we experimentally demonstrate for the first time in the literature dual stage wavelength conversion of QAM signals, in particular, 5 Gbaud 64-QAM, and show that bit error rate below hard-decision forward error correction threshold is only possible with post-compensation of nonlinear distortions. These results are of importance for the development of wavelength routed networks requiring successive wavelength conversion stages to enhance routing capabilities