Effective medium and equivalent circuit analysis of extraordinary transmission through metallic grating in the infrared range

Abstract

Extraordinary transmission (EOT) through one- and two-dimensional deep metallic grating in the infrared range is explored by numerical electromagnetic (EM) field analysis, such as the finite difference time domain method. The transmittance at normal incidence is greater than the porosity that is defined as a proportion of the gap area to the total cross-section when the gap is much smaller than the wavelength of incident infrared light. The EOT mechanism is investigated using two approaches—the equivalent electrical circuit (EEC) model and the effective medium approximation (EMA). The transmittance and reflectance profiles calculated using the EEC model agree with those obtained by the numerical EM analysis. EMA is applied on the basis of the idea that the deep metallic grating can be regard as hyperbolic metamaterials. Then, the effective refractive index of the deep metallic grating is real with a negligible imaginary part, in infrared range. This means that the metallic grating behaves as a dielectric medium, resulting in the great transmission and existence of a Brewster angle.