Extraordinary transmissions on cylinder metallic gratings with very narrow slits

Based on the exact numerical simulations, the transmission resonance for wavelength larger than the period of the grating has not only been obtained in single-layer cylinder metallic gratings with very narrow slits, more interestingly, such a phenomenon has also been observed in multi-layer systems. Comparing the results for the single-layer to those for the multi-layer, we find that the correlation effects are exist in the origin between the transmission resonances in the metallic gratings and the low frequency gaps in the dispersion of photonic crystals. In addition, the effect of absorption on the extraordinary transmission has also been discussed.