Good day,
To calculate the rise budget you will need to estimate the rise time performance of various components such as the transmitter and receiver. This can be measured using the optical and electric time domain viewers (you can use the marker feature to find the 80-20 or 90-10 rise points).
I recommend checking out the following link on the parameters associated with rise time budget calculation (many of these parameters can be set in OptiSystem): https://bohr.wlu.ca/hshodiev/PC481/download/PC481_7%20Part%20II.pdf
Cheers.