Tunneling of Electromagnetic Waves in All-Dielectric Gradient Metamaterials

Abstract

Abstract The nonlocality of optical properties of heterogeneous dielectrics is shown to provide a diversity of tunneling regimes of propagation of infrared radiation through gradient nanostructures, formed by smooth continuous spatial distributions of the dielectric permittivity. These effective regimes of weakly attenuated wave energy transport are stipulated by evanescent modes; the spectral range of these modes is determined by the heterogeneity-induced dispersion of metamaterials, controlled by the shape and geometrical parameters of the spatial distribution of the dielectric permittivity inside the nanostructure. The drastic changes of the optical features of gradient dielectrics, as compared with the homogeneous ones, are illustrated by the formation of heterogeneity-dependent characteristic frequencies, determining the high transparency of gradient nanostructures in the tunneling regimes, the fine structure of frequency-selective subwavelength nanocoatings, and non-Fresnel transmittance spectra of periodical gradient nanostructures. A series of exactly solvable models, describing the tunneling phenomena for flexible multiparameter distributions of the dielectric permittivity, is presented. The peculiarities of reflectance and transmittance spectra of gradient metamaterials arising due to the interplay of natural—plasmon or polariton—and artificial nonlocal dispersion are visualized. The generality of nonlocality-induced tunneling effects is demonstrated by the scalability of the obtained results to microwave tunneling phenomena in transmission lines. The different concepts of electromagnetic wave tunneling through all-dielectric gradient metamaterials are compared.