Multicarrier Digital Backpropagation for 400G Optical Superchannels

Optical superchannels and digital nonlinear mitigation are key technology options to be considered for the deployment of next-generation optical 400G transmission systems. In this paper, we experimentally assess the performance and complexity of multicarrier digital backpropagation (DBP) for dual- and triple-carrier 400G superchannels based on polarization-multiplexed (PM) 16QAM and 64QAM modulation. As an alternative to the widely used nonlinear compensation based on total-field DBP, we demonstrate that a coupled-equations DBP (CE-DBP) approach can be more computationally efficient and also more robust to a nonideal equalization of the receiver front-end in scenarios with limited sampling rate and electrical bandwidth. Employing a triple-carrier PM-16QAM superchannel placed in a 75-GHz slot of a WDM system, we demonstrate an ultralong-haul signal reach of 6600 km using CE-DBP, corresponding to 32% increase relatively to chromatic dispersion equalization (CDE). Targeting an highly spectral-efficient solution for 400G transmission in metro optical networks, these results are extended to a triple-carrier PM-64QAM superchannel placed in a 50-GHz slot, yielding a maximum signal reach of 1750 km through the use of CE-DBP in single-superchannel propagation, corresponding to approximately 60% increase over CDE.