Design and analysis of a long-wave infrared double-layer subwavelength grating polarizer

Subwavelength polarization gratings, as compact and high-performance polarization-selective devices, enable efficient control of polarization channels to meet the requirements of high-dimensional detection. They are widely applied in fields such as remote sensing, material stress detection, and polarization imaging. Based on the conventional single-layer metallic grating structure, this work designs a one-dimensional double-layer metallic polarization grating with a high extinction ratio and high TM-wave transmittance. The structure is optimized and analyzed using effective medium theory and the finite-difference time-domain method. Simulation results show that, within the long-wave infrared band (8–14 μm), the grating achieves TM-wave transmittance ranging from 87% to 98%, with a maximum extinction ratio of 78 dB. Compared with single-layer gratings, the average extinction ratio is improved by approximately 40 dB, significantly enhancing polarization selectivity. Furthermore, the effects of incident angle variation, structural parameter errors, and optical crosstalk between array pixels are analyzed. The presented results provide valuable guidance for the development of metallic wire-grid polarizer arrays with broadband performance, high extinction ratios, and high transmittance.