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提出了一种基于双开口谐振环单元结构超表面的太赫兹宽带涡旋光束产生器. 该结构由金属-电介质两层构成, 位于顶层的是基于双开口谐振环单元结构的超表面, 底层为介质层. 对单元结构阵列进行数值仿真, 圆偏振的入射光可以被转换成相应的交叉偏振透射光, 通过旋转表层金属谐振环, 可以控制交叉偏振透射光具有相同的振幅和不同的相位. 这些单元结构按照特定的规律排列, 可以形成用以产生不同拓扑荷数的涡旋光束的涡旋相位板. 以拓扑荷数1和2为例, 设计了两种涡旋相位板, 数值分析了圆偏振波垂直入射到该涡旋相位板生成交叉圆偏振涡旋光束的特性. 结果表明, 在1.39—1.91 THz的频率范围内产生了比较理想的不同拓扑荷数的涡旋光束, 且透过率高于20%, 最高可达到24%, 接近单层透射式超表面的理论极限值.Terahertz vortex beam generators have potential applications in optical micro-manipulation, terahertz communications and many other fields. A broadband vortex beam generator in a terahertz frequency range is proposed based on the metasurface of double-split resonant rings’ array. The designed structure consists of two layers, i.e., the top layer, which is a metasurface of double-split resonant rings, and the bottom layer, which is the dielectric layer of polymide. The numerical simulation of the cell structure array is performed by using the CST microwave studio. In order to obtain the best performance, the structure parameters of metasurface are continuously optimized and a set of optimal geometric parameters is finally determined. The simulation results show that the circularly polarized incident light can be converted into corresponding cross-polarized transmitted light. By rotating the metal resonant ring on the top layer, the cross-polarized transmitted light can be controlled to have the same amplitude and correspondingly different phases. The relationship between the phase change and the angle of rotation conforms to the P-B phase principle. These cell structures are arranged according to a specific order and can form the vortex phase plates for generating the vortex beams with different topological charges. Taking the topological charge numbers 1 and 2 for example, two kinds of vortex phase plates are designed. The characteristics of the circularly cross-polarized vortex beams generated by a circularly polarized wave perpendicularly incident on the vortex phase plates are numerically analyzed. The results show that the ideal vortex beams with different topological charge numbers are generated. The characteristics of vortex beams appear to be consistent with those theoretical results. Moreover, the vortex beams can be generated in a frequency range from 1.39 THz to 1.91 THz. The operating bandwidth is much wider than the previously obtained result of the transmission terahertz vortex phase plates. The transmission is higher than 20%, and the maximum value of transmission can reach 24%, which is close to the theoretical limit value of the single-layered transmission-type metasurface. This work provides a reference for generating the terahertz vortex beams based on metasurface. It is expected to possess a practical application in generating the device of terahertz vortex beam.
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Keywords:
- terahertz /
- metasurface /
- broadband /
- vortex beam generation
[1] 寇宽, 赵国忠, 刘英, 申彦春 2015 中国激光 42 0815001
Kou K, Zhao G Z, Liu Y, Shen Y C 2015 Chin. J. Las. 42 0815001
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Google Scholar
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Google Scholar
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图 2 在左旋圆偏振波入射下不同旋转角度双开口谐振环单元结构的太赫兹透射特性模拟结果 (a)交叉偏振分量的透射系数; (b)交叉偏振分量的相位改变
Fig. 2. Transmission characteristic of the unit cells with different rotation angle of double-split resonant rings under the left circularly polarized incidence: (a) Transmission coefficients of the cross-polarized component; (b) phase shift of the cross-polarized component.
图 3 两种用于产生拓扑荷数分别为 (a) l = 1和(b) l = 2的涡旋光束超表面
Fig. 3. Schematic of two different designed metasurface for generating vortex beams with topological charges of (a) l = 1 and (b) l = 2
图 4 通过超表面产生拓扑荷数为1和2的涡旋光束的振幅和相位分布. 对于l = 1, 在z = –500 µm平面处的(a)振幅和(b)相位分布. 对于l = 1, 在z = –1000 µm平面处的(c)振幅和(d)相位分布. 对于l = 2, 在z = –500 µm平面处的(e)振幅和(f)相位分布. 对于l = 2, 在z = –1000 µm平面处的(g)振幅和(h)相位分布
Fig. 4. Distributions of the amplitude and phase of the two metasurfaces for generating vortex beams with topological charges of 1 and 2 at 1.7 THz: (a) Amplitude and (b) phase distributions at the plane of z = –500 µm for l = 1; (c) amplitude and (d) phase distributions at the plane of z = –1000 µm for l = 1; (e) amplitude and (f) phase distributions at the plane of z = –500 µm for l = 2; (g) amplitude and (h) phase distributions at the plane of z = –1000 µm for l = 2.
图 5 超表面产生拓扑荷数为1的涡旋光束的振幅和相位分布. 在1.4 THz下, 对于l = 1, 在z = –500 µm平面处的(a)振幅和(b)相位分布; 在1.9 THz下, 对于l = 1, 在z = –500 µm平面处的(c)振幅和(d)相位分布
Fig. 5. Distributions of the amplitude and phase of metasurface for generating vortex beam with topological charge of 1: (a) Amplitude and (b) phase distributions at the plane of z = –500 µm for l = 1 at 1.4 THz; (c) amplitude and (d) phase distributions at the plane of z = –500 µm for l = 1 at 1.9 THz.
表 1 双开口谐振环单元结构仿真优化后的结构参数
Table 1. Optimized parameters of structure based on the double-split resonant rings.
结构参数 结构参数意义 优化值/µm p 单元结构周期 90 a 表层金属谐振环边长 58 d 开口谐振环的开口宽度 11 w 双开口谐振环的金属线宽 11 t1 顶层金属层厚度 0.2 t2 底层介质层厚度 50 
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[1] 寇宽, 赵国忠, 刘英, 申彦春 2015 中国激光 42 0815001
Kou K, Zhao G Z, Liu Y, Shen Y C 2015 Chin. J. Las. 42 0815001
[2] Jansen C, Wietzke S, Peters O, Scheller M, Vieweg N, Salhi M, Krumbholz N, Jördens C, Hochrein T, Koch M 2010 Appl. Opt. 49 E48
Google Scholar
[3] Zhou X D, Li L J, Zhao D, Ren J J 2016 Infrared and Laser Engineering 45 0825001−1
Google Scholar
[4] Wang W, Guo Z Y, Sun Y X, Shen F, Li Y, Liu Y, Wang X S, Qu S L 2015 Opt. Commun. 355 321
Google Scholar
[5] Tan Y H, Li Y L, Ruan H X 2015 Microwave Opt. Technol. Lett. 57 1708
Google Scholar
[6] Karimi E, Schulz S A, Leon I D, Qassim H, Upham J, Boyd R W 2014 Light-Sci. Appl. 3 1
[7] Skidanov R V, Ganchevskaya S V 2016 Proc. SPIE Saratov, September 26-30, 2016 103370R-1
[8] Kirilenko M S, Khonina S N 2013 Optical Memory and Neural Networks 22 81
Google Scholar
[9] Lee W M, Yuan X C, Cheong W C 2004 Opt. Lett. 29 1796
Google Scholar
[10] Ostrovsky A S, Rickenstorff-Parrao C, Arrizón V 2013 Opt. Lett. 38 534
Google Scholar
[11] Liu Y J, Sun X W, Wang Q, Luo D 2007 Opt. Express 15 16645
Google Scholar
[12] Zhou H L, Dong J J, Yan S Q, Zhou Y F, Zhang X L 2014 IEEE Photonics J 6 5900107
[13] Zhang H F, Zhang X Q, Xu Q, Wang Q, Xu Y H, Wei M G, Li Y F, Gu J Q, Tian Z, Ouyang C M, Zhang X X, Hu C, Han J G, Zhang W L 2018 Photonics Res. 6 24
Google Scholar
[14] He J W, Wang X K, Hu D, Ye J S, Feng S F, Kan Q, Zhang Y 2013 Opt. Express 21 20230
Google Scholar
[15] 李瑶, 莫伟成, 杨振刚, 刘劲松, 王可嘉 2017 激光技术 41 644
Google Scholar
Li Y, Mo W C, Yang Z G, Liu J S, Wang K J 2017 Laser Technol. 41 644
Google Scholar
[16] Shi Y, Zhang Y 2018 IEEE Access 6 5341
Google Scholar
[17] Genevet P, Yu N F, Aieta F, Lin J, Kats M A, Blanchard R, Scully M O, Gaburro Z, Capasso F 2012 Appl. Phys. Lett. 100 013101−1
[18] Ding X M, Monticone F, Zhang K, Zhang L, Gao D L, Burokur S N, Lustrac A D, Wu Q, Qiu C W, Alù A 2015 Adv. Mater. 27 1195
Google Scholar
[19] Ding X M, Yu H, Zhang S Q, Wu Y M, Zhang K, Wu Q 2015 IEEE Trans. Magn. 51 1
[20] Hasman E, Kleiner V, Biener G, Niv A 2003 Appl. Phys. Lett. 82 328
Google Scholar
[21] Xu H X, Liu H W, Ling X H, Sun Y M, Yuan F 2017 IEEE Trans. Antennas Propag. 65 7378
Google Scholar
[22] Wang W, Li Y, Guo Z Y, Li R Z, Zhang J R, Zhang A J, Qu S L 2015 J. Opt. 17 045102−1
Google Scholar
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