Advanced C+L-Band Transoceanic Transmission Systems Based on Probabilistically-Shaped PDM-64QAM

We review the most recent, advanced concepts and methods employed in the cutting-edge spectrally-efficient coherent fiber-optic transoceanic transmission systems, such as probabilistic shaping, adaptive digital nonlinear compensation, rate-adaptive spatially-coupled low density parity check codes, and dual-band C+L-band transmission. Building upon all these concepts and methods, we demonstrate transmission of 179 channels carrying a record net data rate of 65 Tb/s over 6,600 km, achieving a spectral efficiency of 7.3 b/s/Hz, and a record average per-channel net bit rate of 363.1 Gb/s. We provide numerical and experimental results, which serve us to comment on the pertinence of the physicist's intuitive measure of performance, the signal-to-noise ratio, vs. the information theorist's more accurate measure, the generalized mutual information, for the systems under study.