Extraordinary optical transmission without plasmons: the s-polarization   case
  It is shown that extraordinary optical transmission through perforated metallic films is possible for s-polarization. Although surface plasmons do not exist for this polarization, their role can be played by a surface wave sustained by a thin dielectric layer on top of the metallic film. This confirms that the existence of a surface wave, whatever its nature, is the responsible for the extraordinary optical transmission phenomenon. 
Esteban Moreno, L. Martin-Moreno, F. J. Garcia-Vidal