ARTIFICIAL UNIAXIAL AND BIAXIAL DIELECTRICS WITH USE OF 2-DIMENSIONALSUBWAVELENGTH BINARY GRATINGS

Two-dimensional symmetric and asymmetric subwavelength binary gratings are investigated. A method for determining the three effective indice s of a two-dimensional (2-D) subwavelength grating is presented, as we ll as a theoretical formalization for the effective index parallel wit h the normal to the surface. It is shown that a 2-D asymmetric binary grating on the surface of a dielectric substrate is analogous to a bia xial thin film. If the grating is symmetric, then the two effective in dices perpendicular to the normal are equal, and the grating is analog ous to a uniaxial thin film. Using these effective indices and the qua rter-wave Tschebyscheff synthesis technique, we designed two- and thre e-level binary gratings to suppress reflections over a broad band. It is shown that for a substrate index of n(s) = 3.0 a three-level 2-D bi nary grating reduced reflections below 0.1% from 8 mu m to 12 mu m.