基于石墨烯超材料表面等离子体激元共振的增强太赫兹调制（英文）

基于表面等离子体共振原理,采用石墨烯超材料设计了开口环结构,用于调制太赫兹波.增加石墨烯的费米能级,改变开口环的开口距离,叠加多层石墨烯以增强石墨烯超材料的共振强度,进而增强太赫兹波调制,调制频率范围包括低频段和高频段.由于石墨烯费米能级的可调谐性,单层结构在高低两个频段的调制深度分别为81%和68%,多层结构在高低两个频段的调制深度分别增加到93%和95%,为动态调制提供了可能.该设计为调制器、吸收体等太赫兹器件的设计提供了指导和借鉴.     

基于石墨烯互补超表面的可调谐太赫兹吸波体

通过在石墨烯超表面设计周期性切条,实现了基于石墨烯互补超表面的可调谐太赫兹吸波体.通过改变外加电压来改变石墨烯的费米能级,吸波体实现频率可调谐特性.研究了石墨烯费米能级、结构尺寸对超材料吸波体吸收特性的影响,并利用多重反射理论研究了其物理机理并且证明了模拟方法的可行性.研究结果表明:当石墨烯费米能级取0.6 eV,基底厚度13μm,石墨烯上切条长宽分别为2.9μm,0.1μm时,吸波体在1.865 THz可以实现99.9%的完美吸收;石墨烯费米能级从0.4 eV增大到0.9 eV,吸波体共振频率从1.596 THz蓝移到2.168 THz,且伴随共振吸收率的改变,吸收率在0.6 eV时达到最大;通过改变费米能级实现的最大吸收率调制度达84.55%.     

石墨烯巴比涅互补结构的太赫兹波透射行为

利用CST电磁场仿真软件模拟设计了基于石墨烯巴比涅互补结构的太赫兹超材料,分别研究了互补层间距、石墨烯费米能级、互补层数对太赫兹波透射谱的影响.模拟结果表明:互补层之间的强烈耦合作用使得太赫兹波的透射得到显著增强;在间距较小时,共振频率随着间距增大而发生蓝移;在间距较大时,共振频率随着间距增大而发生红移,并且透射峰值强度大幅减弱;透射峰频率随着石墨烯费米能级减小而单调减小;增加耦合的互补层数,可使得透射频宽变宽.所设计结构可作为可调控的太赫兹带通滤波器使用.     

臂型网格结构增强石墨烯电调制太赫兹透射

为提高单层石墨烯薄膜电控太赫兹调制器的调制深度,提出一种臂型金属网格微结构与石墨烯结合的太赫兹波透射调制器件.通过臂型金属网格结构激发的共振耦合场增强石墨烯与太赫兹波的相互作用,使石墨烯在外加电压调制下对太赫兹波透射幅度的调制深度获得大幅提升.通过有限元仿真分析了金属结构参数对石墨烯与太赫兹波相互作用增强规律的影响,理论结果表明,臂型网格结构使石墨烯对太赫兹波透射幅度调制深度从7.7%提升到了28.2%.在理论结果的基础上,基于光刻工艺完成了器件的结构制作,实验测试中获得了24%的太赫兹幅度调制深度,且调制深度曲线与理论仿真规律基本一致.     

图案化石墨烯/氮化镓复合超表面对太赫兹波在狄拉克点的动态多维调制

提出一种基于图案化石墨烯/氮化镓肖特基二极管与类电磁诱导透明超表面集成的新型太赫兹调制器.通过施加连续激光或偏置电压改变异质结肖特基势垒,进而致使石墨烯的费米能级在价带、狄拉克点与导带之间移动,使得异质结的电导率发生变化.在太赫兹时域光谱上表现出透射振幅的增减变化,并观察到在狄拉克点上的调制行为.因费米能级接近狄拉克点,对外加光电激励非常敏感,施加4.9—162.4 m W/cm~2的光功率或者0.5—7.0 V的偏压,调制深度先增加后减小,相位差线性增加,其中最大调制深度达90%,最大相位差为189°,该器件实现了太赫兹波的超灵敏多维动态调制.总之,该图案化石墨烯/氮化镓复合超表面调制器在超灵敏光学设备中存在潜在的应用价值.     

基于石墨烯-金属混合结构的可调超材料吸波体设计

利用石墨烯与金属相结合的方法提出了一种新型超材料吸波体结构,通过改变外加偏置电压来改变石墨烯的费米能级,在微波段分别实现了单频和宽频的振幅可调性,并阐述了其电磁吸波及振幅可调的机理。对单一频段下的超材料结构进行了模拟仿真,结果表明,当结构参数不变时,吸波体的吸收强度随石墨烯费米能级的增加而不断减小,最大调制深度达到了58.6%。当石墨烯费米能级为0eV时,吸波体的中心频率随结构参数的改变而改变。基于多吸收峰叠加扩展带宽的原理,利用不同尺寸单元的排列实现了宽频吸波的特性,并通过仿真模拟证明了该宽频吸波体具有振幅可调的性质。     

基于石墨烯的光学控制窄带太赫兹开关（英文）

本文提出了一种光控太赫兹开关,该开关采用覆盖单层石墨烯的十字金属谐振器超表面。利用石墨烯表面电导率模型和有限元法计算了这种复合结构的光谱特性。模拟结果表明,在0.2 W/mm~2的光泵浦后,传输谱(调制深度为36.8%,Q-因子为250)出现了窄带共振衰减现象。另外,这种衰减的调制深度可以通过改变泵浦强度微调节。因此,光学可调谐太赫兹开关的设计将有助于太赫兹通信应用的功能组件开发。     

基于石墨烯的光学控制窄带太赫兹开关

本文提出了一种光控太赫兹开关,该开关采用覆盖单层石墨烯的十字金属谐振器超表面。利用石墨烯表面电导率模型和有限元法计算了这种复合结构的光谱特性。模拟结果表明,在0.2 W/mm²的光泵浦后,传输谱（调制深度为36.8%,Q-因子为250）出现了窄带共振衰减现象。另外,这种衰减的调制深度可以通过改变泵浦强度微调节。因此,光学可调谐太赫兹开关的设计将有助于太赫兹通信应用的功能组件开发。     

太赫兹波段电磁超材料吸波器折射率传感特性

太赫兹超材料吸波器作为一类重要的超材料功能器件,除了可以实现对入射太赫兹波的完美吸收外,还可以作为折射率传感器实现对周围环境信息变化的捕捉与监测.通常从优化表面金属谐振单元结构和改变介质层材料和形态两个方面出发,改善太赫兹超材料吸波器的传感特性.为深入研究中间介质层对太赫兹超材料吸波器传感特性的影响,本文基于金属开口谐振环阵列设计实现了具有连续介质层、非连续介质层和微腔结构的3款太赫兹超材料吸波器,并对其传感特性与传感机理进行了深入研究.结果表明,为了提高太赫兹超材料吸波器的折射率灵敏度、最大探测范围等传感特性,除了可以选用相对介电常数较小的材料作为中间介质层外,还可以改变中间介质层的形态,进而减小中间介质层对谐振场的束缚,增强谐振场与被测分析物之间的耦合.与传统的具有连续介质层的太赫兹超材料吸波器相比,具有非连续介质层和微腔结构的超材料吸波器具有更优越的传感特性,可应用于对待测分析物的高灵敏度、快速检测,在未来的传感领域具有更加广阔的应用前景.     

多功能太赫兹超表面偏振控制器

本文提出了一种“金属栅-开口环/硅环-金属栅”结构的透射式超表面偏振控制器, 研究了入射角度和抽运光对该器件传输及偏振态控制性能的影响. 研究结果表明, 当线偏振太赫兹波垂直入射时, 可对0.39-1.11 THz频段的太赫兹波实现偏振方向90°旋转, 偏振旋转效率为99%, 损耗为1 dB. 对于斜入射的情况, 偏振转换性能在0-60°范围内基本保持不变, 且透过率达到90%以上. 同时, 通过调控抽运光强度的方式, 该器件能够实现对透射与反射太赫兹光束的强度调制, 调制深度均达到90%, 且可以实现太赫兹波偏振分束功能. 该器件可以作为未来太赫兹空间光通信和信息处理的宽带、角度不敏感、可调谐的偏振转换器和分束器.     

Dynamically Tunable and High-Contrast Graphene-Based Terahertz Electro-Optic Modulator

We propose and discuss terahertz(THz) electro-optic modulator induced by periodically patterned graphene microcavity. Due to the joint effect of graphene plasmon resonances and Fabry-Perot(F-P) oscillations, plasmon-induced transparency(PIT) effect is achieved and the operation frequency can be dynamically tuned by graphene Fermi energies and structural parameters. The results reveal that modulation depth(MD) larger than 80% is obtained across a wide frequency range from 4.2 THz to 9.4 THz, and the largest MD and Q factor reaches 95% and 15.8, respectively. In addition, operation frequency range and MD can also be tuned by optimizing the structure parameters. This investigation promises the development of high-performance widely tunable THz modulator in chip integrated photonic circuits.     

Metal–Graphene Hybrid Chiral Metamaterials for Tunable Circular Dichroism

In the field of optoelectronics, circular dichroism (CD) has caused great research interest because it is widely used in imaging and biosensing. A new method for dynamically controlling terahertz (THz) CD in metamaterials is proposed. By introducing chirality and graphene to metamaterials, a pair of chiral structures with completely opposite responses to left-handed circularly polarized (LCP) waves and right-handed circularly polarized (RCP) waves are designed. The influencing factors of CD are explored, including the gap of the structure, the linewidth of graphene, and the Fermi level of graphene. The largest CD (ΔR) is 77%. The CD can be actively modulated in a modulation range of 39–77% and the modulation depth is up to 38%. In addition, two-channel and four-channel chiral metasurfaces for near-field imaging are designed in this way. Good imaging effects and on (“1”) or off (“0”) effects of the multichannel metasurface are demonstrated. This work provides new ideas for the design of tunable metasurfaces and promotes the application of metasurfaces in THz dynamic imaging.     

Polarization-independent terahertz wave modulator based on graphene-silicon hybrid structure

In this study, we propose and demonstrate a broadband polarization-independent terahertz modulator based on graphene/silicon hybrid structure through a combination of continuous wave optical illumination and electrical gating.Under a pump power of 400 mW and the voltages ranging from-1.8 V to 1.4 V, modulation depths in a range of-23%–62% are achieved in a frequency range from 0.25 THz to 0.65 THz. The modulator is also found to have a transition from unidirectional modulation to bidirectional modulation with the increase of pump power. Combining the Raman spectra and Schottky current–voltage characteristics of the device, it is found that the large amplitude modulation is ascribed to the electric-field controlled carrier concentration in silicon with assistance of the graphene electrode and Schottky junction.     

Graphene field effect transistor-based terahertz modulator with small operating voltage and low insertion loss

In this work,we report a broadband terahertz wave modulator based on a top-gate graphene field effect transistor with polyimide as the gate dielectric on a PET substrate. The transmission of the terahertz wave is modulated by controlling the Fermi level of graphene via the polyimide as the top-gate dielectric material instead of the traditional dielectric materials. It is found that the terahertz modulator can achieve a modulation depth of ~20.9% with a small operating gate voltage of 3.5 V and a low insertion loss of 2.1 dB.     

基于石墨烯编码超构材料的太赫兹波束多功能动态调控

提出了一种基于石墨烯带的太赫兹波段的1 bit编码超构材料,可以实现太赫兹波束的数目、频率、幅度等参数多功能动态调控.该结构由金属薄膜、聚酰亚胺、硅、二氧化硅、石墨烯带组成.通过对石墨烯带施加两种不同的电压,可以实现一定频率范围内相位差接近180?的"0"和"1"数字编码单元,进而构成1 bit动态可控的编码超构材料.全波仿真结果表明,不同序列的编码超构材料能够实现波束数目从单波束、双波束、多波束到宽波束的调控.相同序列的编码超构材料,通过施加石墨烯带的不同电压能够实现宽频段波束频率的偏移.对于000000或者111111周期序列的编码超构材料,通过施加石墨烯带的不同电压还能够实现波束幅度的调控.因此这种基于石墨烯带的编码超构材料为灵活调控太赫兹波提供了一种新的途径,将在雷达隐身、成像、宽带通信等方面具有重要的意义.     

石墨烯基双曲色散特异材料的负折射与体等离子体性质

基于有效介质理论研究了石墨烯/介质周期结构的电磁性质, 研究发现这种复合结构的等频面在太赫兹和远红外波段为双曲线, 可用来实现石墨烯基双曲色散特异材料. 通过改变石墨烯的费米能级、介质层厚度和单元结构中石墨烯的层数, 可很容易地调节双曲色散存在的频段. 由于等频面的双曲色散特性, 石墨烯基双曲色散特异材料在远低于截止频率的范围内, 对斜入射的电磁波具有负的能量折射率和正的相位折射率, 并支持局域体等离子体模式. 基于衰减全反射结构, 研究了体等离子体的激发, 探索了体等离子体在可调的光学反射调制器中的应用.     

A tunable dual-band THz absorber based on graphene sheet and ribbons

A tunable terahertz dual band absorber consisted of graphene ribbon arrays and a graphene sheet with near-unity absorption is proposed and studied in this letter. With the coupling enhancement of graphene ribbon and graphene sheet, a perfect dual band absorber with absorption over 99% at 3.67 THz and 5.88 THz is achieved. Moreover, the principal of the coupling enhancement is analyzed. By optimizing the parameters of the structure, not only the absorption can be enhanced, but also the center of absorbing frequency could be shifted. Another approach to adjust the absorber–tuning the chemical potential of graphene which is more convenient and timely is investigated. Furthermore, the sensing of the refractive index is emulated by changing the refractive index of the medium on the top. Results show a broad application prospect of the absorber proposed in this paper.     

A polarization insensitive dual-band tunable graphene absorber at the THz frequency

A dual-band and polarization insensitive tunable graphene absorber for THz frequency has been proposed and investigated. The absorber consists of a square graphene ring with a slit at the middle of each side separated from a metallic mirror by a dielectric spacer. Two distinct absorption peaks of 99.87% and 97.82% are observed at 3.92 THz and 6.96 THz, respectively. In addition, the distributions of electric field intensity are also presented for well-recognized the physical origin of such perfect absorption phenomenon. Furthermore, the influence of geometric parameters on the dual-band absorption properties is studied in detail to provide a useful guidance for practical fabrication. The perfect dual-band absorption properties can also be dynamically tuned through the change of the Fermi energy along with large angle insensitivity, both are interesting for real application. The proposed tunable graphene absorber should found potential applications in areas including sensors, modulators, and detectors.     

Dynamically tunable terahertz passband filter based on metamaterials integrated with a graphene middle layer

The dynamic tunability of a terahertz(THz) passband filter was realized by changing the Fermi energy(E_F) of graphene based on the sandwiched structure of metal-graphene-metal metamaterials(MGMs). By using plane wave simulation, we demonstrated that the central frequency( f_0) of the proposed filter can shift from 5.04 THz to 5.71 THz; this shift is accompanied by a 3 dB bandwidth(? f) decrease from 1.82 THz to 0.01 THz as the EFincreases from 0 to 0.75 eV.Additionally, in order to select a suitable control equation for the proposed filter, the curves of ? f and f_0 under different graphene EFwere fitted using five different mathematical models. The fitting results demonstrate that the Dose Resp model offers accurate predictions of the change in the 3 dB bandwidth, and the Quartic model can successfully describe the variation in the center frequency of the proposed filter. Moreover, the electric field and current density analyses show that the dynamic tuning property of the proposed filter is mainly caused by the competition of two coupling effects at different graphene EF, i.e., graphene-polyimide coupling and graphene-metal coupling. This study shows that the proposed structures are promising for realizing dynamically tunable filters in innovative THz communication systems.