especially at 0.8 b/s/Hz SE; properly capturing coherent WDM crosstalk in numer-
ical simulations for various modulation formats is still a topic of active research
[250, 251]. Another aspect of filter narrowing that is not taken into account in
Table 2.2 is closely related to nonlinear fiber propagation: since OADMs can be
spaced by several hundred kilometers in opti cally routed networks, a modulation
format suitable for high-SE networks has to simultaneously lend itsel f to multiple
passes through OADMs and to nonlinear fiber propagation over appreciable
distances. The impact of joint impairments incurred in this scenario has been
experimentally studied for 40- and 100-Gb/s systems with SEs between 0.4 and
1.0 b/s/Hz using a variety of modulation ...