1 March 2000 Ž . Optics Communications 175 2000 265–273 www.elsevier.comrlocateroptcom Light transmission through metallic channels much smaller than the wavelength S. Astilean a, ) , Ph. Lalanne b , M. Palamaru a a Optics and Spectroscopy Department, Faculty of Physics, Babes-Bolyai UniÕersity, 3400 Cluj-Napoca, Romania b Laboratoire Charles Fabry de l’Institut d’Optique, CNRS, B.P. 147, F-91403 Orsay Cedex, France Received 28 September 1999; accepted 13 December 1999 Abstract A resonant cavity-enhanced light transmission mechanism in metallic gratings with subwavelength apertures is theoreti- cally 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. q 2000 Published by Elsevier Science B.V. All rights reserved. PACS: 78.66.Bz; 73.20.Mf; 42.82.Et Keywords: Sub-wavelength gratings; Rigorous coupled-wave analysis; Surface plasmons Metal gratings with very high transmission effi- ciency have been studied in the past as wire–grid polarizers, selective filters, and beam-splitter ele- ments operating in the far infrared and microwave region where metals can be considered as perfectly Ž wx . conducting see Ref. 1 and references therein . Due to progress in fabrication facilities, there has been recently reawakened interest in the physics govern- ing the electromagnetic behavior of these structures w x for visible light operation 2–5 . The classical prop- erties of perfectly conducting gratings do not hold any longer mainly because of the finite skin depth ) Corresponding author. Fax: q 40-64-191-906; e-mail: sastil@hera.ubbcluj.ro Ž . and surface plasmon SP excitations. Several strik- ing optical responses have been already identified in the visible region. For example, it was recently reported experimentally that subwavelength cylindri- cal nanochannels perforated in optically-thick metal- lic films display unusually high transmission spectra w x in the visible and near-infrared 4,5 . Similarly, for small film thickness, high transmission efficiencies Ž . approaching the unity or enhanced wide band ab- sorptions were also recently observed through ran- wx domly corrugated metallic films 6 or metal islands w x 7,8 . w x In contrast to previous theoretical 3,6 and exper- w x imental 2,7,8 investigations, this paper is dedicated to the transmission through optically thick metallic Ž films film thickness much larger than the skin depth 0030-4018r00r$ - see front matter q 2000 Published by Elsevier Science B.V. All rights reserved. Ž . PII: S0030-4018 00 00462-4