Hello Gagandeep kaur
First of all welcome to optiwave optisystem,i would suggest you to read optisystem mannual for better understanding.There is good explanation of every component.As far as your question is concernd,this is how can we find the sample rAte
It depends upon the Bit rate ,sample you are taking to sample one bit i.e sample/bit and sequence length.
Number of samples=sequence length*sample per bit
Sampling interval=Time window/no. Of samples
Samlpe rate=1/sampling interval
For better informAtion see this link
40 Gb/s Single Channel Transmission in Standard Mode Fibers (SMF)
Regards