Full-Polarization-Sensing MCT Photodetector Enabled by a High-Efficiency Bilayer Plasmonic Metasurface

Mercury Cadmium Telluride (MCT) photodetectors operating in the long-wave infrared (LWIR) band play an indispensable role in infrared sensing and imaging. However, conventional MCT detectors respond only to the intensity of incident light and lack the ability to resolve polarization information—polarization being a critical dimension of the electromagnetic field essential for target recognition and scene understanding in complex environments. We overcome this fundamental limitation by monolithically integrating a compact module composed of six individual bilayer metallic metasurfaces onto a planar junction MCT detector, enabling full-state detection of the polarization state of incident light. The metasurface module includes four linear polarization filters with a peak transmission efficiency of 83% and extinction ratios up to 74 dB, as well as two circular polarization filters achieving a transmission efficiency of 94% and an extinction ratio of 36 dB. The circular polarization functionality is realized by tuning the twist angle between the upper cross-shaped metal nanoparticles and the lower trapezoidal structures, thereby breaking spatial symmetry and inducing strong chiral optical responses. The observed ultra-high efficiency arises from the hybridized coupling between localized surface plasmon resonances (LSPRs) supported by the two metal layers. This fully polarimetric MCT photodetector offers both high efficiency and a compact architecture, demonstrating considerable potential for polarimetric infrared imaging, target detection, and quantum information processing.