I'm now wondering how refraction is considered in DIVA.
I wanted to use dielectric material to make model of lens.
But I think DIVA(or Rhino) models are all made by surfaces.
So even if the model is actually solid (like lens), it won't be regarded as solid.
Could anybody explain the mechanism of refraction in the model made by surfaces?
You are correct in that everything in DIVA will be made up of mesh surfaces. The best thing you can do is to model each side of the lens separately in Rhino, and mesh the geometry yourself using the mesh command in order to keep the result smoothly triangulated.
Refraction by dielectric considers that the surrounding media is a vacuum.