Extended broadband absorption in the visible range with use of the metallodielectric grating structure

This paper presents an analysis of phenomena leading to high and broadband absorption by a structure composed of three elements: two one-dimensional metal and dielectric diffraction gratings and a thick metal layer. A broad spectrum of high absorption in such a structure is attributed to three factors. First, proper design of the structure enables the use of three types of resonances excited at neighboring frequencies: horizontal cavity modes in the dielectric resonators between the metal grating and the metal substrate, vertical cavity modes between the metal strips, and localized surface plasmons excited at the tops of the metal strips and at the bottoms of the vertical cavities. Second, each period of the dielectric grating is built from five strips of identical dimensions but different dielectric constants, which results in frequency splitting due to the different resonance conditions in particular horizontal cavities. Third, the order of the resonators is changed, which assures better coupling efficiency between existing resonances. (paper)