Dear Ifrah,
The FWM nonlinear effect occurs once it meets the necessary conditions of frequency and phase matching. Its effect increases when the propagating wavelengths are close to the zero dispersion wavelength and when the spacing between two neighboring wavelengths is very small. You need to be careful to the different nonlinear effects that could present in the fiber at the same time like SPM, XPF, etc…
You need to make sure that there is no interference to your carrying data wavelength from the other neighboring wavelength to get good quality Q-factor.
I hope this information is helpful. If you need to discuss further, please don’t hesitate to email me at ahmad.atieh@optiwave.com
Regards,
Ahmad