Dual-polarization near-infrared narrow-band unidirectional nonreciprocal thermal radiator

•TE and TM polarization both have nonreciprocal thermal radiation.•Nonreciprocity is greater than 85 % with ultra-high Q factor at angle of 0.8°.•The accuracy of calculation results can be well proved by coupled-mode theory.•The impedance matching theory is used to explain the physical mechanism well. Nonreciprocal thermal radiation is valuable to the energy transmission and collection. Issues of single polarization in near-infrared band with large incident angle cast limitations on the development of nonreciprocal thermal radiation. A dual-polarization narrow-band nonreciprocal thermal radiator in near-infrared band with extremely small incident angle is proposed to address these issues. The radiator consists of periodic annular arrays, magneto-optical medium and metal reflective layer. The simulation results show that the nonreciprocity of two polarizations is greater than 85 % with ultra-high Q factor at the angle of 0.8°. The finite element method and coupled mode theory that are adopted in the study offer high consistent results, which prove the accuracy of calculation results. The physical mechanism of near-infrared narrow-band nonreciprocal radiation is attributed to the excitation of cavity resonance and guided mode resonance. The proposed two-dimensional near-infrared nonreciprocal radiator that allows the dual-polarization operation at small incident angle offers it good potentials in thermal photovoltaic system and energy conversion.