Hello,
Please check the Fiber Bragg Grating component. You should be able to use the built in Apodization functions or load your own profile. That can be set in the component properties window under the Apodization tab. You may access the component datasheet using the Help button, where you would find the file structure.
If you still have question, email me at ahmad.atieh@optiwave.com and let me know the version of OptiSystem that you use. Also, let me know your institution name.
Regards,
Ahmad