Unidirectional thermal radiation from a SiC metasurface

Emission of thermal radiation from periodically patterned surfaces that support surface phonon polaritons has always been into two symmetric emission angles. This is because of the nature of randomness in the thermal spectrum of a hot body that symmetrically distributes the heat into counterpropagating surface waves. Here we demonstrate the design method of metasurfaces with unconventional unit cell dimension and internal structure to direct the thermal radiation into a single specific emission angle. We utilize a combination of diffraction order engineering and numerical optimization techniques for the design process of an ultra-thin metasurface to couple counterpropagating surface waves into a single emission direction. In addition, we compute the near-field incoherent thermal emission intensity from the metasurface by combining the concepts of fluctuation dissipation theorem with solutions of Maxwell's equations based on rigorous coupled-wave analysis and demonstrate unidirectional phaseless thermal radiation emission. The developed approach serves as a tool to design metasurfaces for manipulation of light sources with more complex nature than a plane wave.