Hello Eli,
If I understand you correctly, OptiSystem has bidirectional components that allow feeding back signals to the same component. it is common in lasers as well as for other applications.
You may refer to the examples in OptiSystem Example Library located at the following links for more information and guidance.
C:\Users\USER NAME\Documents\OptiSystem 17.0 Samples\Optical amplifiers\Fiber lasers and amplifiers
C:\Users\USER NAME\Documents\OptiSystem 17.0 Samples\Fiber analysis and design
Regards,
Ahmad