Mid-infrared circular-polarization-sensitive photodetector based on a chiral metasurface with a photothermoelectric effect

Photothermoelectric conversion in chiral metasurfaces with thermoelectric material provides an effective way to achieve circular polarization recognition. In this paper, we propose a circular-polarization-sensitive photodetector in a mid-infrared region, which is mainly composed of an asymmetric silicon grating, a film of gold (Au), and the thermoelectric Bi2Te3 layer. The asymmetric silicon grating with the Au layer achieves high circular dichroism absorption due to a lack of mirror symmetry, which results in a different temperature increasing on the surface of the Bi2Te3 layer under right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) excitation. Then the chiral Seebeck voltage and output power density are obtained, thanks to the thermoelectric effect of Bi2Te3. All the works are based on the finite element method, and the simulation results are conducted by the Wave Optics module of COMSOL, which is coupled with the Heat Transfer module and Thermoelectric module of COMSOL. When the incident flux is 1.0W/cm2, the output power density under RCP (LCP) light reaches 0.96mW/cm2 (0.01mW/cm2) at a resonant wavelength, which achieves a high capability of detecting circular polarization. Besides, the proposed structure shows a faster response time than that of other plasmonic photodetectors. Our design provides a novel, to the best of our knowledge, method for chiral imaging, chiral molecular detection, and so on.