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 6600 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, versus the
information theorist's
more accurate measure, the generalized mutual information, for the systems under study.