高消光比偏振焦平面像元的腔模亚波长临界耦合结构研究

Aiming at the difficulty in the conventional wire grid micro-polarizers in long-wavelength infrared band that the highest extinction ratio can reach only 10:1 due to the limit of diffraction effect and is hard to meet the requirements of high polarization resolution detection, this project proposes a cavity-mode subwavelength critical optical coupling structure constructed on the detecting pixels for breaking through the diffraction limit and to achieve high extinction ratio detection capability due to the suppression of the influence of diffraction by the highly-selective coupling characteristics of cavity modes. Based on the previous accumulations of polarization detection research in non-diffraction regime, by embedding the quantum well photoelectric conversion medium in the microcavity to directly detect the cavity mode, the impact of diffraction effects on cavity mode behavior will be revealed during the progress of reducing the pixel size gradually from 200 microns down to 10 microns to approaching the diffraction limit. The influence of pixel-cavity on polarization-cavity, as well as the coupling efficiency under the combined actions of multi-cavity modes and the impedance matching properties of optical propagation, will be investigated. The characteristics of high-polarization selective coupling will be optimized by the fine plasmonic modulation and the optical-electrical combinatorial manipulation. A quantitative model will be established for optimizing the design of polarization and photo-responsivity under high extinction ratio of 30:1, meeting the technical requirement of focal plane arrays. The attempt of fabricating a prototype device of the polarization imager will be made. The project will provide new physics and design rules for developing the staring type all-solid-state integrated long-wavelength infrared quantum well polarization detection focal plane array imagers. The related results will provide the physical basis for our country to form leading edge in high-sensitivity target recognition and situational awareness.

本项目面向长波红外偏振成像的国家重大需求，针对常规线栅微偏振片衍射限制的最高消光比10:1难以满足高偏振分辨要求的难点，基于前期无衍射限制的偏振探测研究积累，利用腔模高选择性耦合特性对衍射效应影响的抑制来实现高消光比探测，构建突破衍射限制的高偏振选择性像元的腔模亚波长临界光耦合结构。通过微腔中量子阱对腔模的直接探测，研究光敏元尺寸在200~10微米之间逐渐减小到衍射极限的过程中腔模的演变规律、像元腔对偏振腔的影响规律、多重腔共同作用对耦合效率的影响及光传播的阻抗匹配性等特性。采用等离激元光子态深化调控和光-电联合调控对高消光比进行优化，建立定量化模型，完成高消光比30:1下偏振和光响应优化设计，满足焦平面阵列工艺要求，并尝试原理型器件，为发展凝视型全固态集成长波红外偏振成像探测器提供全新的物理机理和设计规则。相关成果将为我国在高灵敏度目标识别和态势感知方面形成领先优势提供器件的物理基础。

本项目面向长波红外偏振成像的国家重大需求，利用腔模高选择性耦合特性对衍射的抑制来实现高消光比探测，构建突破衍射限制的像元腔模亚波长临界耦合结构。完成的研究内容和取得的研究成果如下：..1) 制备成功中心距30x30微米的等离激元微腔量子阱偏振探测超像元，峰值波长在13.5微米附近，偏振消光比高达136:1，成为迄今红外长波集成固态偏振探测像元消光比所报道的最高实验值。该成果突破了衍射极限，确证了像元尺寸下高偏振选择性来自于金属/介质/金属MIM结构微腔的临界耦合特性。排除了像元台面介质腔模对响应线形的干扰，确证了局域表面等离激元模式在像元台面尺度下的唯一性。..2) 利用局域表面等离激元模式进行响应波长调控，不改变电子态，将波长从本征截止波长14.8 微米拓展到16.3微米，10.1%的拓展是已知的光场调控拓展的最大幅度，同时揭示了共振峰值波长与上层金属线宽之间的对应关系。发现移除微腔之间的介质可提升微腔的品质因子，使响应线形变窄同时响应率提升，为光-电联合调控实现更高光谱分辨率和多光谱探测像元集成焦平面提供了物理基础。发现在MIM临界耦合结构中存在与升温过程相关的光电响应淬灭现象，归结为缺陷俘获，其对制定此类探测器的工作条件具有重要的指导意义。..3) 将一维线栅直接做在量子阱介质光栅焦平面像元背面，获得最大像元消光比为47.8。其探测率D*为1.27E10 cm•Hz1/2/W，动态范围为69dB，已能够满足基本的应用需求。..本项目通过上述成果，实现了超高消光比的长波集成超像元红外探测器，掌握了等离激元微腔模式机理及其与量子阱子带跃迁模式之间的耦合规律、光学-电学联合调控突破衍射极限的偏振像元设计规律和优化方法，形成了原理型器件，为发展高性能凝视型全固态集成长波红外偏振成像探测器提供了全新的物理机理和设计规则。相关成果将为我国在高灵敏度目标识别和态势感知方面形成领先优势提供器件的物理基础。