Dual-Polarized Thermal Emission from a Bilayer Twisted-Grating Metasurface

Tailoring thermal radiative properties, including polarization, spectral emissivity, and spatial phase, has attracted an increasing amount of interest in recent years. Polarized thermal emissions can be generated through anisotropic materials, metamaterials, or metasurfaces. Metasurfaces, with the versatile capability to produce differently polarized emissions, have shown significant potential for many advanced photonic applications, such as polarized imaging and chiral molecule sensing. This paper presents a thermal metasurface consisting of two overlapping subwavelength 1D gratings integrated on a single chip, with a relative twist angle that governs the polarization state of the emitted radiation, enabling a transition between dual linear and dual circular polarizations. The spectral emissivity and full set of Stokes parameters of the fabricated metasurface are measured to provide a complete polarimetric characterization. The device exhibits highly polarized, narrowband spectral emission, indicating an enhanced coherence of thermal radiation. The impact of fabrication imperfections on its performance is systematically analyzed. These results highlight the potential of twisted optical metasurfaces for narrowband thermal light sources, infrared imaging, and radiative thermal management applications.