Raytracing methods for gradient-index materials have been available for many years. However, many new applications of gradient-index materials, for example in telecommunications, employ gradient-index elements in situations for which traditional gradient-index raytracing methods are inadequate. A discussion of the limitations fo gradient-index raytracing methods and more exact techniques for modeling propagation through such materials will be discussed.
Thomas J. Bruegge,
"Optical propagation calculations for gradient-index materials", Proc. SPIE 4436, Wave-Optical Systems Engineering, (21 December 2001); doi: 10.1117/12.451288; https://doi.org/10.1117/12.451288