Magnetic field-free circularly polarized thermal emission from chiral metasurface

Thermal radiation from bulk disorderly placed nonresonant emitters is incoherent, broadband and isotropic. In an external magnetic field the thermal radiation from any source is circularly polarized. Here we propose a thermal radiation source which emits circularly polarized radiation and which is not placed in a magnetic field. The thermal source consists of a slab waveguide with etched chiral metasurface. Due to the absence of a mirror symmetry of the metasurface, the thermally generated electromagnetic waves become circularly polarized. In this letter we discuss the origin of this phenomenon in details. Using the Fourier modal method we analyze the eigenmodes of the structure and the emissivity spectra. We demonstrate that the degree of circular polarization in an optimized structure can be as high as 0.87.