Hi,
Are you looking for some kind of diffusion process (as the term “infiltrated” would imply)? If it’s the case, then OptiBPM / OptiMode would be a good match.
If you just want to change the refractive index of the PCF “glass” material, you would need to define a dielectric material in the profiles and materials designer and check the “anisotropic” box. You will then be able to input diagonal elements of the permitivity tensor.