  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.
