Large circular dichroic long-wave infrared polarization photodetector based on rotationally operated chiral metasurfaces

Abstract

A long-wave HgCdTe (MCT) detector, akin to the human eye, cannot inherently discern light polarization. Therefore, a miniature polarization filter needs to be placed in front of the image sensor, which defines the intensity of the different polarization modes. However, the circular dichroism and circular polarization extinction ratios of these miniature polarization detectors are typically not very high in the mid and long wavelength bands, which severely limits the polarization resolving power of the pixels. We numerically simulate a circularly dichroic metasurface based on the silicon material, gradually break the spatial symmetry through displacement and rotation operations of the unit cell of metasurface, and analyze the cause of the large chiral symmetry based on the FP mode and near-field map of the electric field intensity. The resulting high-quality chiral metasurface-based photodetector achieves remarkable circular dichroism and circularly polarized extinction ratios of 0.97 and 20 dB, respectively, promising advancements in microdetector technology from intensity to polarization detection. Last but not least, the use of silicon materials aligns with established silicon-based processes, reducing theoretical process preparation challenges.