Unpolarized Nonreciprocal Thermal Emitters Based on Generalized Transverse Magneto-Optical Effect

In optics and thermal photonics, reciprocity governs and constrains the transportation of light and thermal radiation. Transverse magneto-optical effect is the main mechanism to break reciprocity in propagation, reflection, absorption, and emission. However, it is well-recognized that transverse magneto-optical effect is only valid for transverse magnetic polarization, which is the fundamental constraint in realizing unpolarized or polarization-independent nonreciprocal photonics and thermal photonics. Although the recent reports demonstrate the dual-polarized nonreciprocal thermal emitters based on the rotated incident plane and multimode interaction, it is still unclear the general principle behind a myriad of magnetic configurations and microstructures. More importantly, current dual-polarized thermal emitters are still limited with the non-overlapping angular and spectral properties for both polarizations. In this paper, we reveal the transversal inhomogeneity and the transverse wave nature of light are the generation mechanism of dual-polarized nonreciprocity in arbitrary magneto-optical structures, which is the manifestation of the generalized transverse magneto-optical effect. Moreover, one-dimensional Weyl-semimetal materials-based grating is designed to demonstrate the strong and broadband nonreciprocal thermal radiation, exhibiting an enhanced nonreciprocal radiative heat transfer efficiency superior to the ideal single-polarized nonreciprocal thermal emitters. Our results pave the avenue to unpolarized nonreciprocal photonics and thermal photonics.