Dear Zainab,
you need to make sure that you have an optical null connected to any input port of the components that you use and have no signal. Also, you need to make sure that you add Optical delay element in the path of the backward direction signal to allow the reflected signal to be calculated.
I hope this feedback helps you resolve the issue. if it persist, email me the project as Zip file to ahmad.atieh@optiwave.com and I’ll check it.
Let me know the version of OptiSystem that you use and if you have valid license of OptiSystem.
Regards,
Ahmad