Light transmission through metallic channels much smaller than the wavelength

A resonant cavity-enhanced light transmission mechanism in metallic gratings with subwavelength apertures is theoretically interpreted for operation with visible light. It is shown that under appropriate boundary conditions, the apertures behave as open Fabry-Perot resonant cavities delivering a high photon flux, and that the coupling between the incident light and the fundamental mode supported by the aperture is strongly controlled by surface waves. Compared to the well-known perfect metallic case, we show that the effective index of the fundamental mode strongly depends on the aperture dimension, especially when aperture widths much smaller than the wavelength are considered. Consequently, it is predicted that small variations of aperture shape or dimensions have a huge effect on the transmission properties of real metallic gratings. (C) 2000 Published by Elsevier Science B.V. All rights reserved.