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Terahertz (THz) wave has the advantages of high resolution, large information capacity, easy beam focusing, etc, and can be used in the fields of communication, radar, detection and others. Firstly, as a two-dimensional artificial electromagnetic metamaterial, the coding metasurface is proposed in the microwave band. It uses the digital coding of the electromagnetic wave phase to adjust electromagnetic waves. Subsequently, as an important way to regulate THz, the metasurface extends to terahertz frequency band and becomes a research hotspot. In this paper, we design a coding metasurface based on vanadium dioxide (VO2) with anisotropic characteristics. It is composed of three layers, with a metal cross structure embedded in VO2 at the top, polyimide in the middle, and pure metal at the bottom. The design of the cross shaped structure makes the coding metasurface unit anisotropic, which can provide complete and independent control of the orthogonally linearly polarized incident waves. The pure metal structure at the bottom can provide higher reflection amplitude for the incident wave. And VO2 is introduced into the coding metasurface. As a phase change material, VO2 can switch its properties between the insulating state and the metallic state, which further increases the flexibility of coding metasurface to regulate THz wave. Eight different coding metasurface units are designed in this work. They can be arranged according to a reasonable coding sequence to form a coding metasurface, which consisits of 20×20 metasurface units with an overall size of 2.4 mm × 2.4 mm. Its coding sequence will be changed with the phase of VO2, thus forming a corresponding 1 bit or 2 bit coding metasurface, and the generated beam form changes accordingly. The finite-difference time domain method is used for modeling and implementing simulation, and the results are as follows. The 1-THz orthogonal linearly polarized wave is vertically incident on the coding metasurface. When VO2 is in the insulating state, the designed metasurface can be regarded as an anisotropic 2 bit coding metasurface to generate dual-polarization orbital angular momentum (OAM) vortex beams. The x-polarized vortex wave has an OAM mode number of 2, and the y-polarized vortex wave possesses an OAM mode number of 1. When VO2 is in the metallic state, the designed metasurface can be regarded as an anisotropic 1 bit coding metasurface to generate dual-polarization symmetrical beams. Four reflected waves are generated by incident x-polarized waves, and two reflected waves are created by incident y-polarized waves. The proposed method of combining anisotropy material and phase change material realizes the function of generating multiple THz beams in different forms on the same metasurface. The present results provide a reference for the implementation of multi-functional coding metasurface that can be flexibly applied to multiple scenes.
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Keywords:
- terahertz /
- coding metasurface /
- VO2 /
- anisotropy
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He J W, Dong T, Zhang Y 2020 Infrared Laser Eng. 49 69
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[30] 张璋 2020 博士学位论文 (天津: 天津大学)
Zhang Z 2020 Ph. D. Dissertation (Tianjin: Tianjin University) (in Chinese)
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图 1 编码超表面单元结构 (a)俯视图; (b)侧视图; (c)底部
Figure 1. Schematic of the coding metasurface unit: (a) Top view; (b) side view; (c) bottom.
图 2 VO2处于绝缘态时, x极化波(a)和y极化波(b)单元的电流分布; VO2处于金属态时, x极化波(c)和y极化波(d)单元的电流分布
Figure 2. When VO2 is insulating state, surface current of x-polarized wave (a) and y-polarized wave (b) unit; when VO2 is metallic state, surface current of x-polarized wave (c) and y-polarized wave (d) unit.
图 3 (a)—(d) VO2处于绝缘态时, 单元在正交极化波垂直入射下的反射幅度和反射相位 (a), (b) x极化波; (c), (d) y极化波. (e)—(h) VO2处于金属态时, 单元在正交极化波垂直入射下的反射幅度和反射相位 (e), (f) x极化波; (g), (h) y极化波
Figure 3. (a)–(d) When VO2 is insulating state, the reflection amplitude and phase of the units under the vertical incidence of the orthogonal polarized wave: (a), (b) x-polarized wave; (c), (d) y-polarized wave. (e)–(h) When VO2 is metallic state, the reflection amplitude and phase of the units under the vertical incidence of the orthogonal polarized wave: (e), (f) x-polarized wave; (g), (h) y-polarized wave.
图 4 (a)各向异性编码超表面编码序列; (b)各向异性编码超表面示意图; (c), (d) VO2为绝缘态, x极化波(c)与y极化波(d)垂直入射时的编码序列; (e), (f) VO2为金属态, x极化波(e)与y极化波(f)垂直入射时的编码序列
Figure 4. (a) Anisotropic coding metasurface coding sequences; (b) diagram of anisotropic coding metasurface; (c), (d) VO2 is insulating state, the coding sequence when the x-polarized wave (c) and y-polarized wave (d) are incident vertically; (e), (f) VO2 is metallic state, the coding sequence when the x-polarized wave (e) and y-polarized wave (f) are incident vertically
图 5 模式l = 2的涡旋波 (a)远场方向图; (b)相位图. 模式l = 1的涡旋波 (c)远场方向图; (d)相位图
Figure 5. Vortex beam with mode l = 2: (a) Far-field diagram; (b) phase diagram. Vortex beam with mode l = 1: (c) Far-field diagram; (d) phase diagram.
图 6 (a) 对称的4束反射波; (b)对称的2束反射波
Figure 6. (a) Symmetrical four-beam reflected wave; (b) symmetrical two-beam reflected wave.
图 7 不同形式的远场波束
Figure 7. Different forms of far-field beams.
表 1 8个编码超表面单元结构参数
Table 1. Structure parameters of eight coding metasurface units.
单元 1A 1B 2C 2D 3A 3B 4C 4D X/μm 60 76 81 96 60 76 81 96 Y/μm 60 60 76 76 81 81 96 96 M/μm 76 76 96 96 76 76 96 96 N/μm 76 76 76 76 96 96 96 96 
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表 2 不同状态下的波束形式
Table 2. Beam form in different states.
正交极化波入射 x极化波入射 y极化波入射 VO2绝缘态 l = 2的涡旋波 l = 1的涡旋波 VO2金属态 对称的4束反射波 对称的2束反射波
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[1] Kleine Ostmann T, Nagatsuma T 2011 J. Infrared Milli. Terahz Waves 32 143
Google Scholar
[2] Tonouchi M 2007 Nature Photon. 1 97
Google Scholar
[3] Yang X, Pi Y M, Liu T, Wang H J 2018 IEEE Sens. J. 18 1063
Google Scholar
[4] Yang Q, Qin Y, Zhang K, Deng B, Wang X, Wang H 2017 Microw. Opt. Technol. Lett. 59 2048
Google Scholar
[5] Nagel M, Haring B P, Brucherseifer M, Kurz H, Bosserhoff A, Büttner R 2002 Appl. Phys. Lett. 80 154
Google Scholar
[6] 贺敬文, 董涛, 张岩 2020 红外与激光工程 49 69
He J W, Dong T, Zhang Y 2020 Infrared Laser Eng. 49 69
[7] Yu N, Genevet P, Kats M A, Aieta F, Tetienne J, Capasso F, Gaburro Z 2011 Science 334 333
Google Scholar
[8] Cui T J, Qi M Q, Wan X, Zhao J, Cheng Q 2014 Light-sci. Appl. 3 e218
Google Scholar
[9] 白毅华, 吕浩然, 付鑫, 杨元杰 2022 中国光学快报 20 012601
Google Scholar
Bai Y H, Lü H R, Fu X, Yang Y J 2022 Chin. Opt. Lett. 20 012601
Google Scholar
[10] Huang H F, Xie S H 2021 OSA Continuum. 4 2082
Google Scholar
[11] 李佳辉, 张雅婷, 李吉宁, 李杰, 李继涛, 郑程龙, 杨悦, 黄进, 马珍珍, 马承启, 郝璇若, 姚建铨 2020 物理学报 69 228101
Google Scholar
Li J H, Zhang Y T, Li J N, Li J, Li J T, Zheng C L, Yang Y, Huang J, Ma Z Z, Ma C Q, Hao X R, Yao J Q 2020 Acta Phys. Sin. 69 228101
Google Scholar
[12] Pan Y B, Lan F, Zhang Y X, Zeng H X, Wang L Y, Song T Y, He G J, Yang Z Q 2022 Photonics Res. 10 416
Google Scholar
[13] Liu S, Cui T J, Xu Q, Bao D, Du L L, Wan X, Tang W X, Ouyang C M, Zhou X Y, Yuan H, Ma H F, Jiang W X, Han J G, Zhang W L, Cheng Q 2016 Light Sci. Appl. 5 e16076
Google Scholar
[14] Yu S X, Li L, Shi G M 2016 Appl. Phys. Express 9 082202
Google Scholar
[15] Li Z L, Wang W, Deng S X, Qu J, Li Y X, Lü B, Li W J, Gao X, Zhu Z, Guan C Y, Shi J H 2022 Opt. Lett. 47 441
Google Scholar
[16] Li J S, Li S H, Yao J Q 2020 Opt. Commun. 461 125186
Google Scholar
[17] Yasir Saifullah, 杨国敏, 徐丰 2021 雷达学报 10 382
Google Scholar
Yasir S, Yang G M, Xu F 2021 J. Radars 10 382
Google Scholar
[18] 唐小燕, 柯友煌, 井绪峰, 别寻, 李晨霞, 洪治 2021 光子学报 50 150
Tang X Y, Ke Y H, Jing X F, Bie X, Li C X, Hong Z 2021 Acta Photon. Sin. 50 150
[19] Wang H, Ling F, Zhang B 2020 Opt. Express 28 36316
Google Scholar
[20] Li C Q, He C H, Song Z Y 2022 IEEE Photon. J. 14 1
Google Scholar
[21] 杨欢欢, 曹祥玉, 高军, 李桐, 李思佳, 丛丽丽, 赵霞 2021 雷达学报 10 206
Google Scholar
Yang H H, Cao X Y, Gao J, Li T, Li S J, Cong L L, Zhao X 2021 J. Radars 10 206
Google Scholar
[22] Bai X D 2020 Results in Phys. 18 103334
Google Scholar
[23] Li J S, Chen Y 2022 Appl. Opt. 61 4140
Google Scholar
[24] 闫昕, 梁兰菊, 张雅婷, 丁欣, 姚建铨 2015 物理学报 64 158101
Google Scholar
Yan X, Liang L J, Zhang Y T, Ding X, Yao J Q 2015 Acta Phys. Sin. 64 158101
Google Scholar
[25] Li J H, Zhang Y T, Li J N, Li J, Yang Y, Huang J, Ma C Q, Ma Z Z, Zhang Z, Liang L J, Yao J Q 2020 Opti. Commun. 458 124744
Google Scholar
[26] Ren Z R, Liu Y Q, Wang Y, Lu L, Qi K N, Yin H C 2022 IEEE Access 10 50479
Google Scholar
[27] Wu L W, Ma H F, Gou Y, Wu R Y, Wang Z X, Xiao Q, Cui T J 2022 Nanophotonics 11 2977
Google Scholar
[28] 封覃银, 裘国华, 严德贤, 李吉宁, 李向军 2022 中国光学 15 387
Feng T Y, Qiu G H, Yan D X, Li J N, Li X J 2022 Chin. Opt. 15 387
[29] Liu X B, Wang Q, Zhang X Q, Li H, Xu Q, Xu Y H, Chen X Y, Li S X, Liu M, Tian Z, Zhang C H, Zou C W, Han J G, Zhang W L 2019 Adv. Opt. Mater. 12 1900175
[30] 张璋 2020 博士学位论文 (天津: 天津大学)
Zhang Z 2020 Ph. D. Dissertation (Tianjin: Tianjin University) (in Chinese)
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