The experimental results in Figure 14.30 correspond to the largest capacity
reported after a transoceanic distance at the time of publication. It has been
obtained with 149 channels at 40 Gbit/s rate, totalizing 6 Tbit/s capacity [24].
This represents more than 50% capacity improvement when compared with the
largest reported capacity at 10 Gbit/s, even if the transmission distance is smaller
in the 40 Gbit/s-based experiment.
More recently, the same capacity was transmitted with a modulation format
different from than (RZ)DPSK, namely Return to Zero Quadrature Phase Shift
Keying (RZ-DQPSK). This format still relies on PSK, but over four possibly phase
states instead of two for (RZ)DPSK. Despite its natural compatibility with very
high capacities (e.g., ...