Hi Bhagyalaxmi,
you can find multimode graded index fiber in this path:
Default/Multimode Library/Optical Fibers/
there are three types of fibers. one of them is titled “Measured-Index Multimode Fiber”
in this fiber the refractive index profile can be defined as one of three built-in profiles (parabolic index, Alpha profile, Step index) and more over you can insert the refractive index “From File”.
So for your question, I suggest to save your refractive index in a file then upload it to OptiSystem.
the file should have two colons. the first colon is the radius in microns and the second colon is the real value of the refractive index.
I encourage you to check the manual of the suggested fiber for more information.
Good luck,
thank
Mohamed