Ultra-broadband wide-angle perfect absorber in the visible regime through a thin grating–insulator–metal structure

Abstract

A new thin grating-insulator-metal (GIM) structure with ultra-broadband wide-angle perfect absorption is proposed, and a general approach to this kind of multilayered structure is investigated based on the rigorous coupled-wave analysis method and the transfer matrix method. On the basis of this approach, the electromagnetic field distributions in each layer and optical diffraction coefficients are derived theoretically. Compared with a metal–insulator–metal (MIM) structure, the GIM structure consisting of a metal grating on top of a low-loss dielectric layer and a bottom metal layer can achieve a higher absorption with the smaller thickness that attributes to the extraordinary optical transmission of the top grating layer and the cavity resonance of the middle insulator layer. By optimizing the structural and material parameters, the materials from top to bottom are selected as Mn-Al2O3-Mn, whose thicknesses are 10 nm, 65 nm, and 70 nm, respectively. With these optimum parameters, better performance with average absorption over 95% in the visible regime is obtained. Furthermore, this structure retains near-perfect broadband absorption for large incidence angles and different polarizations. The conclusions presented here could have potential applications in optical devices, such as optical displacement detection and visible light absorption.