Tunable wideband-directive thermal emission from SiC surface using bundled graphene sheets

Abstract

Coherent thermal radiation emitters based on diffraction gratings inscribed on surface of a polar material, such as silicon carbide, always possess high angular dispersion resulting in wideband-dispersive or monochromatic-directive emission. In this paper, we identify roots of the high angular dispersion as the rapid surface phonon polariton (SPhP) resonance of the material surface and the misalignment of the dispersion curve of the diffraction orders of the grating with respect to light line. We minimize the rapid variation of SPhP resonance by compensating the material dispersion using bundled graphene sheets and mitigate the misalignment by a proper choice of the grating design. Utilizing a modified form of rigorous coupled wave analysis to simultaneously incorporate atomic-scale graphene sheets and bulk diffraction gratings, we accurately compute the emissivity profiles of the composite structure and demonstrate reduction in the angular dispersion of thermal emission from as high as ${30}^{\ensuremath{\circ}}$ to as low as ${4}^{\ensuremath{\circ}}$ in the SPhP dominant wavelength range of 11--12 $\ensuremath{\mu}\text{m}$. In addition, we demonstrate that the graphene sheets via their tunable optical properties allow a fringe benefit of dynamical variation of the angular dispersion to a wide range.