How to reduce FWM impact?

One method to reduce FWM effects is to use transmission fiber that has high chromatic dispersion coefficient at the signal wavelength such as standard single-mode fiber SSMF (ITU-T G.652). The typical chromatic dispersion coefficient of SSMF is 18 ps/nm ⋅ km @ 1550 nm which helps to significantly reduce FWM from occurring. Even a lower chromatic dispersion coefficient significantly helps in reducing FWM such as NZ-DSF fiber (ITU-T G.655). This fiber is specially designed with low chromatic dispersion coefficient (~4 ps/nm ⋅ km @ 1550 nm) for extended transmission distance but high enough to significantly reduce FWM effects.

To reduce these effects is to lower signal power in the fiber or use fiber with a larger cross sectional area to reduce the signal power density.

A third method to help reduce FWM effects is to space signal channels unevenly. 

A fourth method to reduce FWM effects is to use DWDM systems with wide channel spacing. The magnitude of FWM effect is dependent on channel spacing. Wider spaced   

DWDM channels generate weaker FWM components.