Grating resonances as an alternative to plasmon resonances in nanophotonics applications

We present a mini-review on the discovery, nature and characterization of the specific family of natural modes existing on periodic arrays of both dielectric and metallic sub-wavelength scatterers, and the corresponding to them resonances in the optical-range wave scattering and absorption. These grating modes (G-modes) have been studied analytically for the gratings of thin flat strips and those of circular wires. It has been shown that, for infinite gratings, their complex-valued natural frequencies tend to the Rayleigh anomalies if the cross-sectional area of the strip or wire becomes smaller. Therefore their quality factors, in this idealized case, display unlimited growths. For finite-size gratings the G-mode quality factors are finite and controlled by the number of elements. If they are made of noble metals and their number is in hundreds, the G-modes have much higher quality factors than the better-known surface-plasmon modes. Therefore the former have potential to replace the latter in the design of sensors in applications related to the detection of changes in the refractive index of the host medium.