Broadband Unidirectional Thermal Emission Enhancement of Phase‐Gradient Metasurface Based on Surface Plasmon Polaritons

Abstract

Compared with external coherent light manipulation, the realization of unilateral‐oriented thermal emission is more challenging. Although a specific metasurface is confirmed of the angular selectivity, the emissivity is generally mirror‐symmetric along the surface normal for uncorrelated phases between different positions of the thermal source. Here, from the metallic patch array conditions derived for unilateral thermal emission, a phase‐gradient metasurface in combination with surface plasmon polaritons is demonstrated which exhibit wide‐angled unilateral enhancements of thermal emission while the radiations in the symmetric directions are suppressed. By directly heating the device to 120 °C, the acquired spatial thermal emission spectrums indicate that at a wavelength of λ = 11.5 µm, the changed emissivity 0.61–0.46 with the orientation angle from 10° to 40° is asymmetric to 0.32–0.21 from −10° to −40°. Dealing with the phase response of meta‐atoms, the proposed method and phase‐modulated structure are helpful for the direction of controllable thermal emission.