Double-band perfect absorber based on the dielectric grating and Fabry-Perot cavity

To realize double-band perfect absorption, in this paper, we present a theoretical study of plasmonic absorption based on a metal-dielectric grating nanostructure. The structure consists of subwavelength periodic Al2O3 grating covered with metal grating with a metal substrate. Results show that the one of the two absorption bands is caused by the Fabry-Perot resonance in the gold grating slits, and the other absorption band is caused by the gap plasmonic resonance of the Al2O3 dielectric grating. The effect of structural parameters on absorption is also studied, the field distribution of the proposed nanostructure is presented to illustrate the absorption mechanism. Moreover, the two absorption peaks can be adjusted individually with different geometrical parameters. The results will pave the way towards the design of double-band plasmonic perfect absorber, which may have potential application in plasmonic absorption switch, plasmonic sensors and photodetectors.