Resonance transmission or absorption in deep gratings explained by magnetic polaritons

Resonance transmission or absorption has been observed in metallic deep gratings and previously characterized as coupled surface plasmon polaritons or Fabry-Perot-like resonances. This letter provides a quantitative explanation of this phenomenon by means of localized magnetic polaritons. Rigorous coupled-wave analysis is used to predict the spectral transmittance and absorptance of subwavelength gratings. The resonance condition is compared with that predicted by the LC circuit model. Some geometric effects that cannot be explained by previous models can be well understood in terms of magnetic polaritons. The insight gained from this study may facilitate future design and applications of subwavelength periodic structures. (C) 2009 American Institute of Physics. [doi:10.1063/1.3226661]