Tunability of non-plasmon resonances in e-polarized terahertz wave scattering from microsize graphene strip-on-substrate gratings

Abstract

We consider the scattering and absorption of the E-polarized plane wave by the infinite grating of flat graphene strips lying on flat dielectric substrate. To build a trusted full-wave meshless algorithm, we cast the scattering problem to the dual series equations and perform its analytical regularization based on the use Inverse of Discrete Fourier Transform. Then, the problem reduces to a Fredholm 2nd-kind matrix equation for the unknown Floquet harmonic amplitudes. Therefore, the convergence of the resulting code is guaranteed by the Fredholm theorems. Numerical experiments show that such a configuration is a frequency-selective metasurface or one-periodic photonic crystal. If the grating period and substrate thickness are micrometer-sized, the resonance frequencies of such a cavity are in the terahertz range. As plasmon modes are absent in the E-polarization case, these resonances correspond to low-Q slab modes of the substrate, slightly perturbed by the presence of grating, and ultrahigh-Q lattice modes of the whole grating as a periodic open cavity. We quantify their effect both using our full-wave numerical code and deriving the asymptotic analytical expressions for the lattice-mode frequencies and Q-factors.