Dear Amirhossin,
we recommend using either the Fiber Bragg Grating component in OptiSystem at the location Default/Filters Library/Optical/FBG/ or using OptiGrating software to design your FBG. If you use OptiGrating, then you may use OptiGrating component in OptiSystem and load your transmission and emission spectra to the component and use it in your project. The OptiGrating component is located at Default/Optiwave Software Tools/.
Regards,
Ahmad