摘要
针对现有太赫兹手性超表面吸收器在工作频率单一、效率不足以及结构复杂性方面等问题,提出了一种基于温度响应的二氧化矾(VO_(2))材料的双波段太赫兹手性超表面吸收器。通过理论分析和电磁仿真,验证了超表面在1.93 THz和3.83 THz频率上的圆二色性(CD)分别达到0.91和0.82。利用温度调控VO_(2)的电导率,实现了对超表面CD的动态调节,展现了良好的调控灵活性。同时,通过调节顶层与金属衬底之间的法布里-珀罗共振,实现了CD从双波段到单波段的转换,并利用这一特性,该结构能够在两个频率下针对不同偏振光生成不同的成像信号,从而实现数字成像功能。此外,进一步解释了超表面产生手性响应的物理机制,并讨论了结构参数与入射角对超表面性能的影响。所提出的超表面不仅具有优异的性能,而且结构设计简单,在太赫兹波段的手性光探测、高灵敏度传感器以及其他光电集成系统中展现出广泛的应用潜力。
Objective With the rapid advancement of information technology and the increasing depth of research on metasurfaces,the static and uncontrollable nature of traditional metasurfaces has limited their further development.As a result,dynamically tunable chiral metasurfaces are in high demand across many application fields.Vanadium dioxide(VO_(2)),a novel two-dimensional material with dynamic tunability,offers significant potential in this regard.In recent years,the integration of metasurfaces with VO_(2) has led to the design of various dynamically tunable metasurfaces.However,most of the proposed tunable chiral metasurfaces feature complex unit structures,suffer from low efficiency in practical applications,and are limited to single-band functionality.Therefore,when designing new chiral metasurface devices,factors such as material loss,structural simplicity,and the tunability of achievable functionalities must be considered.These challenges have become a critical topic in current research on chiral metasurfaces.Methods The metasurface we designed consists of a three-layer unit cell(Fig.1).The bottom layer is a metallic reflective layer,the middle layer is a dielectric layer made of Topas(cyclic olefin copolymer),and the top layer is composed of a composite material of VO_(2) and gold.The top-layer resonant pattern comprises two sets of semicircular arcs and rectangular patches.Each semicircular arc,with a width of w,is connected to a rectangular patch with a length of l_(1) at its outer edge.Both sets of elements are made of gold and are arranged in a centrosymmetric configuration to form the overall resonant structure.The left gold rectangular patch is extended by a rectangular VO_(2) patch with a length of l_(2).Other parameters include period of P,representing the period of the unit cell.The bottom gold layer serves to suppress electromagnetic wave transmission,with its thickness set to 0.1μm to ensure that all incident electromagnetic waves are reflected.The dielectric layer is made of Topas,which has a relative permittivity of 2.57.Characterized by transparency,thermally stable,and exhibits excellent optical properties,this material demonstrates negligible absorption coefficient in the terahertz range.The thickness of the dielectric layer is h_(1).The top layer has a thickness of h_(2),with the ring’s width w,outer radius R,gold rectangular patch length l_(1),and VO_(2) rectangular patch length l_(2).Through simulation,the optimized geometric dimensions of the structure are as follows:l_(1)=10μm,l_(2)=6μm,R=14μm,w=5μm,h_(1)=15μm,h_(2)=1.5μm,P=50μm.In the simulations,we use CST Microwave Studio software to calculate the optical properties of the structure through full-wavesimulations in the frequency domain.Periodic boundary conditions are applied along the x-axis and y-axes for the basic unit cell,with the light source incident along the−z direction.Open boundary conditions are set along the z-axis.Results and Discussions We have proposed a dual-band terahertz chiral metasurface based on VO_(2) material.The designed structure achieves remarkable circular dichroism(CD)responses of up to 0.91 and 0.82 at 1.93 THz and 3.83 THz,respectively,demonstrating excellent dual-band performance(Fig.2).The dynamic tunability of the chiral response is enabled by the phase transition properties of VO_(2) between its insulating and metallic states(Fig.3).Additionally,leveraging the Fabry‒Pérot resonance effect between the top layer and the metallic bottom layer,the circular dichroism response can be switched from dual-band to single-band by adjusting the thickness of the dielectric layer(Fig.3).Based on this characteristic,we designed a multi-frequency circularly polarized wave detection and image encryption scheme.By combining single-band and dual-band metasurfaces,the system generates distinct imaging signals for different polarized waves at two frequencies(Fig.7),enabling multiplexed digital imaging functionality.Conclusions In summary,we have proposed a design for a dynamically tunable dual-band chiral metasurface absorber based on VO_(2) material.Theoretical results show that when VO_(2) is in its metallic state,the metasurface achieves left-circularly polarized(LCP)absorption rates of up to 98.56%and 93.90%at 1.93 THz and 3.83 THz,respectively,while the absorption rate for right-circularly polarized(RCP)is less than 12%across the 1‒4 THz.The CD values at the two resonant frequencies,1.93 THz and 3.83 THz,are 0.91 and 0.82,respectively.When VO_(2) is in its insulating state,the CD effect is significantly reduced.By adjusting the conductivity of VO_(2),the optical response of the metasurface can be effectively controlled,enabling selective absorption of circularly polarized light in different states.Additionally,due to the Fabry‒Pérot resonance,the CD response can be switched from dual-band to single-band by varying the thickness of the dielectric layer.Furthermore,based on terahertz near-field imaging,this structure shows potential applications in dual-frequency circularly polarized wave detection and image encryption.
作者
张艺心
邓仕杰
刘厚权
Zhang Yixin;Deng Shijie;Liu Houquan(Guangxi Key Laboratory of Optoelectronic Information Processing,Guilin 541004,Guangxi,China;School of Optoelectronic Engineering,Guilin University of Electronic Technology,Guilin 541004,Guangxi,China)
出处
《光学学报》
北大核心
2025年第9期297-304,共8页
Acta Optica Sinica
基金
广西自然科学基金(桂科AB23075134,2024GXNSFDA010062)
国家自然科学基金(62205079,62364006,U23A20282)
桂林电子科技大学研究生教育创新计划项目(2025YCXS231)。
关键词
圆二色性
超表面
可切换特性
吸收器
circular dichroism
metasurface
switchable feature
absorber
