Dear Rafie,
As Aadil said, OptiSystem doesn’t have LFBG component. However, you may use OptiGrating to design the LFBG then load the transmission and emission spectra to OptiSystem through the OptiGrating component that can be found at Default/Optiwave Software Tools/ and use it in the project.
FYI, we are in process of adding TFBG into OptiSystem.