Enhanced transmission via cavity modes in gratings formed by subwavelength metallic cylinders

Abstract

In the last few decades, special attention has been paid to the optical response of structures composed of periodic subwavelength slits in thin metallic sheets. Extraordinary transmission and evanescent-to-propagating conversion are two of the main effects that have been most investigated in these systems. In this paper, we present an alternative way of enhancing the intensity diffracted by a grating through morphological electromagnetic resonances. Unlike nanoslit arrays, in this system the cavities are formed by periodically distributed chains of metallic subwavelength cylinders, which behave like walls that confine the fields and thus show resonant behavior. The set of cavities is illuminated by an evanescent wave generated by total internal reflection. We show that resonant coupling of cavity modes excited by the inhomogeneous wave produces enhanced transmission of up to 92% and also that the system has the ability of steering most of the transmitted intensity in a particular direction given by the diffraction orders. The results are compared with those obtained from a similar structure formed by periodically distributed perfectly conducting solid walls.