基于超表面的多波束多模态太赫兹涡旋波产生  

Multi-beam multi-mode vortex beams generation based on metasurface in terahertz band

作　　者：李国强[1,2] 施宏宇[1,2] 刘康 李博林 衣建甲 张安学[2] 徐卓[1,4] Li Guo-Qiang;Shi Hong-Yu;Liu Kang;Li Bo-Lin;Yi Jian-Jia;Zhang An-Xue;Xu Zhuo(MOE Key Laboratory for Multifunctional Materials and Structures,Xi’an Jiaotong University,Xi’an 710049,China;School of Information and Communications Engineering,Faculty of Electronic and Information Engineering,Xi’an Jiaotong University,Xi’an 710049,China;College of Electronic Science and Technology,National University of Defense Technology,Changsha 410073,China;Electronic Materials Research Laboratory,Key Laboratory of the Ministry of Education,Xi’an Jiaotong University,Xi’an 710049,China)

机构地区：[1]西安交通大学,多功能材料和结构教育部重点实验室,西安710049 [2]西安交通大学电子与信息学部信息与通信工程学院,西安710049 [3]国防科技大学电子科学学院,长沙410073 [4]西安交通大学,电子陶瓷与器件教育部重点实验室,西安710049

出　　处：《物理学报》2021年第18期353-359,共7页Acta Physica Sinica

摘　　要：太赫兹涡旋波束可以被用于高速通信及高分辨率成像,其产生方式近年来受到了越来越多的关注.本文提出了一种反射型超表面,它可以在太赫兹频段产生四种不同模态的涡旋波束.超表面单元结构基于几何相位原理,由三层结构组成,上下两层为金属结构,中间层为介质,其上层金属结构由圆环及椭圆贴片构成.利用几何相位对圆极化波的调控作用,可以实现由线极化波到圆极化波的分解,并实现对不同圆极化波的灵活调控.为了同时调控反射波的偏转方向,本文利用平面反射阵列原理来计算每个超表面单元所需的相位补偿.通过相位叠加原理,在不同传播方向的波束中叠加不同模态的轨道角动量,较好地实现了太赫兹频段复杂波束的调控效果.仿真及测试结果表明设计的超表面能够在太赫兹频段产生带有±1和±2模态的4个波束,在无线通信及高分辨率成像等方面有潜在应用价值.The generating of vortex beams in the terahertz(THz)band attracts significant attention due to their applications in high-speed communication and high-resolution imaging.In this article,a novel reflective metasurface working in the THz band is designed to generate four vortex beams with different topological charges in different directions.The unit cell is designed based on the geometric phase,and it consists of two metallic(gold)layers and one dielectric layer in between.The top layer of the unit cell includes an elliptic patch and a circular ring,and the bottom layer of the unit cell is a metallic ground.The reflection efficiency of the unit cell is very high due to the presence of metallic ground.To break through the limitations of traditional methods,the metasurface is a good choice to generate beams that carry orbital angular momentum(OAM).Using the concept of geometric phase,the reflection phase of reflective circular polarization(CP)electromagnetic waves can be controlled in an ingenious way.Owing to the property of the geometric phase,inverse phase shift can be achieved for left-handed circular polarization and right-handed circular polarization waves.By utilizing this trait of geometric phase,one can decompose a linear polarization wave into two orthogonal circular polarization waves and control their properties respectively.By rotating the top layer of the unit cell,360-degree phase shift and the phase distribution satisfying the requirement for generating the multi-beam multi-mode vortex beam can be achieved.In order to control the direction and the topological charge of each beam,based on the geometric phase,the theory of reflectarray and the phase composition principle,the phase distribution of the reflective metasurface is calculated to provide the phase compensation to make the vortex beams point to certain directions.It is worthwhile to point out that the method presented in this paper provides a way to generate complex multi-mode vortex beams in the THz band.The simulations and measurements show

关 键 词：太赫兹涡旋 波束调控 超表面 

分 类 号：O441.4[理学—电磁学] TB34[理学—物理]