Low Complexity Advanced DBP Algorithms for Ultra-Long-Haul 400 G Transmission Systems

We experimentally assess the performance versus complexity tradeoff of advanced split-step and Volterra-based digital backpropagation (DBP) techniques, applied to aWDM (75-GHz flexigrid) ultra-long-haul (ULH) transmission system composed of five dual-carrier PM-16 quadratic-amplitude modulation 400 G superchannels. Using the recently proposed weighted Volterra series nonlinear equalizer (W-VSNE), we demonstrate a maximum reach improvement of 600 km, obtained at the expense of only six DBP steps for an entire >5000-km optical link (1000 km/step), representing a ~90% reduction on the total number of DBP steps relatively to the widely used split-step Fourier method (SSFM) implementation. The W-VSNE technique is also shown to be more accurate than the correspondent weighted SSFM (W-SSFM) algorithm when applied in medium (10-50 DBP steps) and low complexity (<;5 DBP steps) regimes. The achieved reduction of computational effort (up to 88%), together with the associated latency savings (up to 90%), demonstrates the feasibility of low complexity and efficient DBP for high-speed ULH transmission systems.