基于拓扑优化的薄液晶灵活调控太赫兹波编码超表面  

Flexible Modulation of Terahertz-Wave-Coded Metasurface in Thin Liquid Crystals with Topological Optimization Design

作　　者：张亚杰 栾迦淇 李潮龙 陈羽 郜定山 赵茗 李培丽[1] Zhang Yajie;Luan Jiaqi;Li Chaolong;Chen Yu;Gao Dingshan;Zhao Ming;Li Peili(Faculty of Electronic and Optical Engineering,College of Flexible Electronics(Future Technology),Nanjing University of Posts and Telecommunications,Nanjing 210023,Jiangsu,China;Wuhan National Laboratory for Optoelectronics,Huazhong University of Science and Technology,Wuhan 430074,Hubei,China)

机构地区：[1]南京邮电大学电子与光学工程学院,柔性电子(未来技术)学院,江苏南京210023 [2]华中科技大学武汉光电国家研究中心,湖北武汉430074

出　　处：《光学学报》2024年第11期232-243,共12页Acta Optica Sinica

基　　金：武汉光电国家研究中心开放基金(2022WNLOKF012)。

摘　　要：提出并研究了一种基于拓扑优化设计的太赫兹薄液晶(LC)编码超表面。基于遗传算法对金属谐振图案进行拓扑优化,设计了一种薄厚度反射型2 bit LC编码超表面单元,LC层厚度仅为14μm,克服了利用多层LC或LC谐振切换机制实现多比特编码外部馈电系统复杂的缺点,同时具有较快的响应速率。基于设计的LC 2 bit编码超表面单元,利用遗传算法对阵列编码排布进行逆向设计,增强波束调控的主动性和灵活性,仿真实现了0.394 THz处波束赋形和涡旋波束的功能。结果表明:对于波束赋形,该超表面单元不仅可以实现俯仰角在0°~30°范围内、方位角在0°~360°范围内任意角度的单波束和多波束的调控,还可以对多波束的各个目标波束进行独立调控,同时扫描和跟踪多个目标,实现对太赫兹波束更优性能的调控;对于涡旋波束,该超表面单元可以产生拓扑荷数l=±1、±2、±3且模式纯度大于70%的涡旋波束,同时可实现俯仰角在0°~30°范围内、方位角在0°~360°范围内任意角度的单涡旋和多涡旋波束的灵活调控。Objective Encoding metasurfaces based on tunable materials can achieve dynamic control of terahertz beams with reconfigurability under the action of external control and are the main solutions to the design of encoding metasurfaces in terahertz bands.The liquid crystal(LC)is a more practical solution than other tunable materials because of its mature processing technology,low manufacturing cost,and simple driving scheme.However,most of the relevantly reported LCcoded metasurfaces employ one-bit encoding,inevitably producing symmetric beams and limiting the beam deflection efficiency to only 50%.Increasing the LC layer number and exploiting the resonance switching mechanism of LCs in different regions are two options to achieve multi-bit encoding,but will increase the complexity of the external voltage manipulation system.Meanwhile,since the corresponding rate of LC integrated devices is mainly related to the thickness of LCs,the design of thin LC multi-bit-coded metasurface cells with low voltage control based on simplifying the external voltage control has certain research significance and good application prospects.Additionally,for the encoding sequence design,under plane wave excitation,the traditional method is to adopt gradient phase encoding and complex encoding to independently regulate single and multiple beams.Meanwhile,there will be some limitations on the initiative,flexibility,and deflection accuracy of the design of the beam regulation encoding.Thus,we employ the genetic algorithm for the reverse design of the encoding sequence,which can overcome the shortcomings of traditional methods.Methods Compared to the optimization of the underlying shape and structural parameters,topological optimization by dividing the surface pattern into equal-sized pixel units is generally combined with optimization algorithms to increase the design freedom and yield better performance and has been widely applied to the design of various functional devices for metasurfaces.First,we aim at the achievable 2 bit encoding and

关 键 词：表面光学 编码超表面 拓扑优化 液晶 波束控制 涡旋波束 

分 类 号：O436[机械工程—光学工程]