Far-infrared perfect optical absorption in film supporting metallic grating structures

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 electric field and energy flow density distributions and absorption dispersion for the POA were 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. The waveguide modes in the film is demonstrated to play an important role for the perfect absorption, which significantly change the energy loss region, but with negligible effect on the POA resonant peak width, besides the Fabry-Perot resonant modes in the grating slits and the surface plasmon polaritons excited on the surfaces. 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.