You can model refraction using waves in a water-tank; the waves slow down in shallow water, and speed up in deeper water. You can do things like make lenses. S

You can model refraction using waves in a water-tank; the waves slow down in shallow water, and speed up in deeper water. You can do things like make lenses. So I suppose a near-zero refractive index would be modeled by a region of "infinite depth". Is there a relationship between wavelength and depth, such that for a given wavelength, there is some finite depth that behaves for practical purposes as if it were infinite?