Hello Ankita sharma,
I guess your problem has more to do with bidirectional fiber itself.Besides the typical global simulation parameters of OptiSystem, such as Bit rate, Samples per bit and Sequence length, there are two additional parameters that are very important when designing bidirectional systems or systems with closed loops, such as ring networks. I suggest you to have a look at this link and go through it. It would definitely help you.
Lesson 5: Bidirectional Simulation — Working with Multiple Iterations
Regards