Resonant optical transmission through thin metallic films with and without holes

Using a rigorous electromagnetic analysis of two-dimensional (or crossed) gratings, we account, in a first step, for the enhanced transmission of a sub-wavelength hole array pierced inside a metallic film, when plasmons are simultaneously excited at both interfaces of the film. Replacing the hole array by a continuous metallic film, we then show that resonant extraordinary transmission can still occur, provided the film is modulated. The modulation may be produced in both a one-dimensional and a two dimensional geometry either by periodic surface deformation or by adding an array of high index pillars. Transmittivity higher than 80% is found when surface plasmons are excited at both interfaces, in a symmetric configuration.