长波红外偏振探测器能够大幅提升对热成像目标的识别能力。受制于衍射极限的物理限制，目前的微线栅偏振片型长波红外偏振探测器的偏振消光比基本上只能做到最高10∶1左右。文中采用金属/介质/金属的等离激元微腔结构，将量子阱红外探测激活层相嵌在微腔之中。由于上、下金属之间的近场耦合形成了在双层金属区域的横向法布里-珀罗共振模式，构成等离激元微腔。文中利用微腔的模式选择特性及其与量子阱子带间跃迁的共振耦合，将量子阱子带跃迁不能直接吸收的垂直入射光耦合进入等离激元微腔并转变为横向传播，从而能够被量子阱子带吸收，实现了在长波红外13.5 μm探测波长附近偏振消光比大于100∶1的结果。相关工作为发展我国高消光比长波红外偏振成像焦平面提供了全新的物理基础和技术路径。

The long wavelength infrared polarimetric detector can greatly improve the recognition ability of thermal imaging. Owing to the physical limitation of the diffraction limit, the polarization extinction ratio of the current micro-grid polarizer-type long wavelength infrared polarimetric detectors can basically only be as high as about 10∶1. In this paper, a metal/dielectric/metal plasmonic microcavity structure has been fabricated, with the infrared detection active layer of the quantum wells being embedded inside the microcavity. Due to the near-field coupling between the upper grating and bottom reflector metals, a lateral Fabry-Perot resonance was established in the double-metal region, forming the plasmonic microcavity. Benefited from the mode selection characteristics of the microcavity and its resonant coupling with the quantum well intersubband transition, the normal incident light, which cannot be directly absorbed by the intersubband transition of the quantum wells, was coupled into the plasmonic microcavity, transforming its propagation direction into lateral and being absorbed by the quantum wells. The mechanism was confirmed by finite element simulation and the microcavity key parameters such as the grating width and the thicknesses were designed and optimized. Such a structure was applied to the detecting pixels sized at 27 × 27 μm, which was suitable for focal plane arrays. Resulting from the capture and confinement of the incident photons, the detectivity of the detecting pixels could be promoted by about one order of magnitude comparing to the un-structured 45^o edge facet coupled detector fabricated from the same epitaxy wafer. The polarization extinction ratio greater than 100∶1 at about 13.5 μm of detecting peak wavelength in the long wavelength infrared waveband was achieved, while the peak intensity dependence on the polarizer azimuth angle fitted Malus law very well. Such a work provides a novel physical foundation and technical route for the development of high extinction ratio long wavelength infrared polarimetric imaging focal planes.