Inter-Channel Crosstalk Cancellation for Nyquist-WDM Superchannel Applications

Superchannel WDM systems employ narrow channel spacing to achieve high spectral efficiency and increase channel capacity. Additionally, these systems attempt to avoid inter-channel interference (ICI) and inter-symbol interference (ISI), by creating and maintaining both spectral and temporal orthogonality. This in turn imposes a strong requirement on the spectral amplitude and phase of the received signals. For Nyquist-WDM systems, the temporal shapes are Nyquist pulses, requiring uniform spectral density with flat phase. In practice, these requirements are only partially achieved, resulting in non-ideal Nyquist systems with inter-channel interference (ICI). We propose and demonstrate two joint ICI cancellation methods based on our new “super receiver” architecture, which jointly detects and demodulates multiple subchannels simultaneously. The maximum a posteriori (MAP) algorithm is most readily implemented for systems with channel spacing equal to the baud rate, and the adaptive linear equalizer is effective for all channel spacings. Simulation results show that both joint ICI cancellation schemes outperform conventional linear equalization, approaching the performance of an isolated single channel.