GRIN-like dielectric slab lens through effective index engineering

A GRIN-like dielectric slab lens has been studied through 2D FDTD simulations. The focusing structure can be described as a thin dielectric slab with sub-wavelength index engineering, formed by air gaps (or filled with a different refractive index material) of identical sizes. The concentration of the number of gaps varies radially and makes the dielectric slab a smoothly graded-index media, which gives it focusing or diverging properties.