Grating resonances on periodic arrays of sub-wavelength wires and strips: From discoveries to photonic device applications

Abstract

This chapter reviews the nature and the history of discovery of the high-quality natural modes existing on periodic arrays of many sub-wavelength scatterers as specific periodically structured open resonators. Although such modes can be found on various finite and infinite arrays made of metallic and dielectric elements, we concentrate our discussion around infinite arrays of silver wires and strips in the optical range. The grating modes (G-modes), like any other natural modes, are the “parents” of the corresponding resonances in the electromagneticwave scattering and absorption. Their wavelengths in either case are determined mainly by the period and the angle of incidence that has been a reason of their misinterpretation as Rayleigh anomalies. On the frequency scans of the reflectance or transmittance coefficients, G-mode resonances are usually observed as Fano-shape (double-extremum) spikes, while in the absorption they always display conventional Lorentz-shape peaks. If a grating is made of sub-wavelength size noble-metal elements, G-modes exist together with better known localized surface-plasmon modes (LSP-modes) whose wavelengths lay in the optical range. Thanks to high tunability and considerably higher Q-factors, the G-mode resonances can potentially supplement or even replace the LSP-mode resonances in the design of nanosensors, nanoantennas, and nanosubstrates for solar cells and surface-enhanced Raman scattering.