Extraordinary optical properties in the subwavelength metallodielectric free-standing grating

In this paper, we present a free-standing metallodielectric grating structure that can achieve multiple transmission dips and peaks at normal incidence over the visible spectrum. The amount of dips and peaks can be adjusted by the thickness of dielectric film. In our proposed structure, there are three types of resonance modes supported: Surface plasmon polarition (SPP) at horizontal metal/dielectric interface, vertical cavity mode in the metal slits, and guide mode in the dielectric film. Physically the coupling and resonant interactions among these modes lead to the generation of dips and peaks in the transmission spectrum. The transmission peaks is further interpreted by using Fano resonance. More surprisingly, the simultaneous excitation of three types of resonance modes can enhance the field distribution, which results in unexpected nearly perfect absorption in such simple structure. Moreover, compared to other absorption peaks, this high absorption peak originates from that guide mode resonance in the dielectric film inhibits transmission induced by cavity mode resonance in the metal slits. These results can be used in the design of many photonics components.