Twisted bilayer gratings for high-efficiency circular polarization detection in the infrared spectrum

Polarization detection imaging is a crucial technology that leverages the polarization characteristics of light to enhance imaging capabilities. Traditional circular polarization detection systems rely on bulky and costly optical elements, limiting their integration into compact focal plane detectors. In this work, we propose and analyze a twisted bilayer grating structure composed of silicon and aluminum (or silver) to achieve high circular polarization extinction ratio (CPER) in the infrared range of wavelength. Using FDTD simulations, we systematically optimize the structural parameters, including grating width, thickness, twisted angle, and interlayer spacing. Our results demonstrate that the CPER peak could be found in between wavelength of 4μm to 5μm for both aluminum-silicon and silver-silicon bilayer gratings with 1μm period.