FAR-INFRARED PERFECT OPTICAL ABSORPTION IN FILM SUPPORTING METALLIC GRATING STRUCTURES

Abstract

Perfect optical absorption (POA) in the far-infrared region is demonstrated in the subwavelength metallic grating structure with a supporting dielectric film, and the features of the POA are investigated by theoretical calculation and analysis under normal transverse magnetic polarized incident light. In this study, a simple structure design was first proposed to achieve nearly perfect absorption in the far-infrared region. The dependence of the POA on the geometry was calculated by rigorous coupled wave analysis. Furthermore, the electromagnetic field and energy flow density distributions and the absorption dispersion for the POA are investigated by numerical simulations. Results show that the POA in the far-infrared region is obtained using the film supporting metallic grating structure with the advantages of linear tunability on the POA wavelength and simple structure design with a large geometric tolerance. Besides the Fabry-Perot resonance modes in the grating slits and the surface plasmon polaritons excited on the surfaces, the waveguide modes in the film are also demonstrated in the thick film case, which significantly change the energy loss region, but with negligible effect on the POA resonant peak width. The advantages of wavelength linear tunability, simple structure design, and large geometric tolerance of the POA in the far-infrared region demonstrate its promising application in infrared sensing, detection, and modulation. Keywords: Absorption, Surface plasmon polaritons, Subwavelength grating structure, Waveguide modes