Parametric behavior of diffraction on guided-mode resonant grating of subwavelength thickness

TL;DR

This paper analyzes the diffraction behavior of subwavelength dielectric gratings, revealing their ability to achieve full reflectance and transparency windows due to parametric effects and unique guided-mode properties.

Contribution

It introduces a coupled-mode theory with three parameters to describe diffraction on subwavelength gratings and identifies conditions for full reflectance and transparency windows.

Findings

Gratings can achieve full reflectance in narrow frequency bands.

Sinusoidal profile gratings lack guided mode coupling, enabling transparency windows.

Parametric evanescent field enhancement occurs near the grid.

Abstract

We consider Wood anomalies in diffraction spectrum from two-dimensional dielectric periodic grid embedded in a surrounding media. The grid is of subwavelength thickness, and diffraction of wave having S-polarization is investigated in the vicinity of the emergence of first diffraction maximum. We reduce Maxwell equations to coupled-mode theory with three parameters, which are integral characteristics of material arrangement in the grid. In particular, we show that such grids are capable to have full reflectance in parametrically narrow frequency bandwidth. The effect is accompanied by a parametric evanescent field enhancement in the region near the grid. In particular, we consider grids with sinusoidal profile and show that this type of grids possesses unique diffraction properties due to absence of the guided mode coupling. For such grids, there is a thin transparency window at a background of near to zero transmission at slightly nonnormal incidence. We estimate what are enough grid size and the incident beam flatness to resolve the singularities.