Abstract
Recently a new structure showing a super-enhanced transmission [Optics Commun. 209, 17–22 (2002); Phys. Rev. B, 67, 155314, (2003)] has been proposed. The origin of this phenomenon was not clearly explained. In this paper, by using a numerical Order-N FDTD spectral method, we study the eigenmodes, the band structure and the dispersion curves of a photonic 2-D crystal made with coaxial circular cavities and made from a real metal. We show that the super-enhanced transmission of the finite structure is due to a cavity resonance of a single guided mode. An extensive characterization of this mode is presented, in terms of the spatial mode structure and effective index dispersion curve.
Highlights
As reported in reference [2], we studied the influence of the physical parameters on the transmission spectra of this annular aperture array (AAA)
We study the band structure of a photonic crystal made of coaxial cavities, made from a perfect metal
In this paper we have established that the transmission enhancement obtained by a AAA structure is a cavity resonance due to a single guided mode through the coaxial cavities
Summary
Ebbesen [1] published a very interesting paper showing enhanced transmission of light through a subwavelength circular aperture array in a metallic film. That paper has stimulated many studies on this subject. A short bibliography can be found in reference [2]. Structures showing an enhanced transmission are 1-D lamellar gratings [3] or 2-D arrays made of cylindrical cavities in the metallic film [4]. For such a 2-D structure, the transmission is significantly enhanced but remains small: experimentally an 8% zero order transmission is observed through a circular hole grating in gold (hole diameter 200 nm, lattice constant 600 nm, metal thickness 250 nm [4])
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