Dear Eli,
please refer to the examples in OptiSystem Example Library for guidance and information on SOAs. You can find related examples at the following links.
C:\Users\USER NAME\Documents\OptiSystem 17.1 Samples\Component sample files\Amplifiers Library\Optical\SOA
C:\Users\USER NAME\Documents\OptiSystem 17.1 Samples\Optical amplifiers\Semiconductor optical amplifiers
You can also find the theory about any component used in OptiSystem in the datasheet that can be access by clicking on Help button in the component properties popup window or in the document OptiSystem_Component_Library.pdf
Regards,
Ahmad