Optical coherent systems have an optimum transmission rate, at which some mitigation of non-linear effects spontaneously takes place.

The phenomenon occurs at a Baud rate which is neither the one of serial systems (28-32 GBaud) nor that of OFDM systems (in the hundreds of MBaud per subcarrier). It actually occurs between 2 and 8 GBaud, depending on system parameters. The higher the dispersion, the lower the optimum rate and, typically, the greater the potential mitigation.

In our OFC 2015 paper:

The EGN model (download EGN model paper) provides excellent accuracy in predicting the amount of non-linearity (or non-linear interference noise, NLI) affecting each channel in a WDM system.

See below the June 2014 news for more details. However, the EGN model is substantially more complex than the GN model. 

Three OptCom papers on non-linearity modeling and system impact have been accepted at ECOC 2014. They make use of the high-accuracy non-linear propagation EGN model to perform advanced studies of special system conditions. They can be dowloaded directly below.