Dr. Gabriel Charlet, of Bell Labs France, is presenting a paper on how subsea cable systems are now capable of supporting 100Gb/s and how he believes that next gen systems may carry as much as 400Gb/s and 1Tb/s.

One of the first points he makes is that 400Gb/s is already available for terrestrial systems.  The difference is that the reach of the cables is far shorter than in subsea systems.  Charlet explains that the answer to this is Spectral Efficiency.  It would been to be improved by at least a factor of five.

To reach the 1Tb/s, Charlet experimented with a few methods.  One was a quad carrier experiment, which appears to be multiple 400Gb/s working in tandem.  QPSK offers the longest reach.

His work in reaching higher capacity is ongoing.