Dear hayder ali.
To understand how fwm can be mitigated, you need to under what fwm is and how this occurs.
eg. A dispersive media has low fwm effects..
Becoz two photons with differents wavelenths travel with different speeds and hence are far apart to participate in any quatum interaction.
That is also a reason we never used dispersion shifted fiber becoz zero dispersion in fiber will lead to fwm.
Besides you can cpsk modulation to suppress fwm
With ragards