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多频点多波束可调的全空间太赫兹编码超表面

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提出了一种通过改变二氧化钒的相变状态,实现太赫兹波在透射、反射之间灵活切换且多频点多波束可调的全空间太赫兹编码超表面。仿真结果表明:当二氧化钒处于绝缘态时,在频率f1=0。6 THz的左旋圆极化波(LCP)垂直入射下,设计的编码超表面可以视为3-bit Pancharatnam-Berry(PB)几何相位编码超表面,产生透射的拓扑荷数为1的涡旋波;当二氧化钒处于金属态时,设计的编码超表面可以视为双频点独立可调的1-bit各向异性反射型编码超表面。频率f2= 0。5 THz的正交线极化波(x与y极化波)垂直入射时,该编码超表面可以产生两种不同形式的对称波束;频率f3= 0。85 THz的正交线极化波垂直入射时,可以实现雷达散射缩减和对称波束。这对设计多功能的太赫兹波束调控器件有一定的借鉴意义。
Multi-Frequency and Multi-Beam Tunable Terahertz Coding Metasurface in Full Space
Objective Terahertz waves refer to electromagnetic waves between microwave and infrared wave,which can be applied in different fields such as communication,sensing,radar,and imaging.Terahertz coding metasurface,as an important device for modulating terahertz waves,has the advantages of simple structure,small size,low cost,low loss,and high efficiency.The coding metasurface units are arranged according to a certain coding sequence,and by changing the phase difference between the units,the flexible modulation of terahertz waves can be achieved to generate various forms of beams.However,when the design of a general terahertz coding metasurface is completed,the function and operating frequency are relatively single.In order to fully utilize the coding metasurface,an anisotropic metasurface is proposed,which can regulate the incident orthogonal polarized waves separately.And a frequency independent coding metasurface has been proposed,which can separately regulate the incidence waves at different frequency points to generate different forms of beams.In addition,the phase change materials such as vanadium dioxide(VO2)were used to achieve the switching of transmission and reflection modes of terahertz waves,thereby achieving the goal of full spatial modulation of electromagnetic waves.The above methods improve the ability of the coding metasurface to regulate terahertz waves,but the integration level still needs to be improved.Therefore,we integrate these technologies to achieve multi-frequency and multi-beam tunable terahertz coding metasurface in full space,greatly improving its ability to regulate terahertz waves.Methods In this paper,a coding metasurface which can regulate the circular polarized waves and orthogonal polarized waves separately is proposed by combining the principle of PB geometrical phase as well as the frequency independence and anisotropy of double crosses.In addition,introducing the phase change material VO2,flexible switching of terahertz waves between transmission and reflection is achieved by changing its phase change state.The details are as follows.When VO2 is in an insulating state,the designed coding metasurface is a single-frequency-point 3-bit PB geometrical phase transmitting coding metasurface,which generates transmission-type vortex waves with topological charge number of 1.When VO2 is in a metallic state,the designed coding metasurface is a dual-frequency-point independently adjustable 1-bit anisotropic reflective coding metasurface,which generates four symmetric beams,of which two symmetric beams on the xoz plane with RCS reduction and two symmetric beams are on the yoz plane,respectively.Results and Discussions The designed coding metasurface units(Fig.1)with identical metallic split-ring structures in the third,fifth,and seventh layers are rotated from 0° to 157.5° in a step of 22.5° to obtain a total of eight coding metasurface units(Fig.2).When VO2 is in an insulating state and a circularly polarized wave with f1 =0.6 THz is incident,the units maintain a high transmission amplitude and strictly satisfy a phase difference of 45°.The design conditions for a 3-bit transmission type coding metasurface unit are met.Arranging them according to a certain coding sequence[Fig.4(b)]can produce transmission-type vortex waves with topological charge number of 1(Fig.5).When VO2 is in a metallic state and the orthogonal polarized waves of f2 =0.5 THz and f3 =0.85 THz are incident,a dual-frequency and anisotropic 1-bit reflective-type coding metasurface unit(Fig.3)is designed by using the two cross structures.After arranging them according to a certain coding sequence[Figs.4(c)-(f)],the perpendicular incidence of y-polarized wave with f2=0.5 THz on the xoz plane produces two symmetric beams[Figs.6(a)and 6(b)].When a y-polarized wave with f3=0.85 THz is incident vertically,two symmetric beams are generated on the yoz plane[Figs.6(c)and 6(d)].When a x-polarized wave with f2 =0.5 THz is incident vertically,four symmetrical beams are generated[Figs.7(a)and 7(b)].When a x-polarized wave with f3 =0.85 THz is incident vertically,a diffuse scattering beam can be generated[Figs.8(a)and 8(b)],realizing RCS reduction.The results show that with the rational design of the coding metasurface combined with the phase transition state of VO2,the frequency of the incident wave source,and the polarization state,the full space regulation of terahertz wave's reflection and transmission can be realized and five beam forms on the same coding metasurface can be obtained.Conclusions In this paper,a coding metasurface with full space multi-frequency and multi-beam tunability is designed by changing the phase transition state of VO2,combining the principle of PB geometrical phase and the cross unit structure with dual-frequency anisotropy.A 3-bit transmission coding metasurface with an operating frequency of f1 =0.6 THz is designed to produce a transmitted vortex beam.And a dual-frequency 1-bit anisotropic reflective coding metasurface with operating frequencies of f2 =0.5 THz and f3 =0.85 THz is designed to produce various forms of symmetric and scattered beams.This coding metasurface,which introduces phase change material and realizes full space multi-frequency multi-beam regulation by transmission and reflection,is important for designing multifunctional terahertz beam modulation devices.

optics at surfacesterahertzfull spacetunabilitycoding metasurfacemulti-beam

杨志雄、汪静丽、孙文俊、尹亮、董先超、万洪丹、陈鹤鸣、钟凯

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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

南京邮电大学贝尔英才学院,江苏 南京 210023

天津大学精密仪器与光电子工程学院,教育部光电信息技术重点实验室,天津 300072

表面光学 太赫兹 全空间 可调 编码超表面 多波束

国家自然科学基金国家自然科学基金江苏省自然科学基金江苏省自然科学基金武汉光电国家研究中心开放基金横向课题多功能太赫兹天线的研究资助项目

1217419961571237BK20221330BK201515092022WNLOKF0122021外323

2024

光学学报
中国光学学会 中国科学院上海光学精密机械研究所

光学学报

CSTPCD北大核心
影响因子:1.931
ISSN:0253-2239
年,卷(期):2024.44(4)
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