There are a lot of different fiber types and a lot of different fiber applications. Do you have a particular application in mind? A classic example of an optical fiber is passive step index telecom fiber. Some important design criteria are the core diameter, the cladding diameter, and the second order mode cut off wavelength.
You can use Comsol Multiphysics to design optical fiber by simulation of the profiles parameters and get the interactions of propagated light through this profile.