渔网电磁超介质左手通带的超常透射及其电场增强效应的数值研究

本文利用电磁场数值模拟方法研究了分布矩形孔阵列的"金属-电介质-金属"三明治渔网电磁超介质在其左手通带发生的超常透射现象和不同模式激发下的电场增强效应。结果证实左手通带紧邻的超常光学传输峰源于波导共振模式,利用超常传输效应可以有效降低电磁超介质的损耗,提高左手性能;波导共振模和左手通带对应的反对称磁模能够分别在孔洞和金属夹层区域激发超过11倍的增强电场,因此渔网电磁超介质结构在表面增强光谱和传感等方面也具有潜在应用价值。     

一维带限Weierstrass分形分层地面与矩形截面导体柱复合电磁散射FDTD研究

运用时域有限差分方法研究一维带限分形分层粗糙地面与矩形截面导体柱的复合电磁散射,计算复合电磁散射的双站散射系数,得到复合散射系数随散射角的变化,讨论粗糙面高度起伏均方根、分维、中间层介质、下层介质及矩形截面导体柱的参数等对复合散射系数的影响.     

基于辅助电介质层的棱镜表面等离子体共振效应研究

研究了一种基于棱镜基底-辅助电介质层-金膜-待测介质四层结构的表面等离子体共振(surface plasmon resonance,SPR)效应激励模型.采用薄膜光学与波导理论,探索了由辅助电介质层与金膜复合而成共振薄膜对SPR效应的激励机理与调制特性.借助时域有限差分方法,数值模拟得到辅助电介质层属性与共振能量传输特性关系.在此基础上,构建了波长调制型棱镜辅助电介质层结构SPR激励系统.研究结果表明,当待测介质折射率相同时,相较基于棱镜基底-金膜-待测介质三层结构的Kretschmann激励模型,辅助电介质层激励模型共振光谱整体向长波方向偏移且半波宽度出现显著展宽效应.而当待测介质折射率增大时,辅助电介质层型激励模型的共振光谱不仅会向长波方向偏移,而且折射率响应灵敏度比棱镜Kretschmann三层激励模型高出75%.因此该模型能够为诸如高灵敏度检测、新型光学滤波与调制器件设计等领域的研究应用提供理论与实践储备.     

基于电子共振跃迁的光频本征型超常电磁介质

超常电磁介质因其异于普通材料的电磁性质而受到广泛关注,基于周期性谐振结构的超常介质(即超材料)到光频段以后会出现加工困难,且损耗明显,而基于材料本征性质的超常介质却表现出独特的优势.文章简要介绍了三类本征型超常电磁介质的形成机制,它们分别是强各向异性机制、自旋波和等离子体耦合机制以及电子共振跃迁机制.重点介绍了基于电子共振跃迁的超常介质.采用半经典理论分析了气态介质中二能级、三能级体系的电偶极跃迁和磁偶极跃迁过程,总结了极化率和磁化率的一般表达式,综述了基于二能级、三能级及多能级模型获得的气态超常电磁介质.此外,对凝聚态体系中的电子共振跃迁和超常电磁性质关系作了简要阐述.最后,对采用实验方法实现的这种本征型超常电磁介质进行了简要分析.     

基于全介质超表面的电磁诱导透明研究

设计了一种基于TiO2介质的全介质电磁诱导透明超表面模型,该结构由两根十字垂直交叉的介质棒和四个介质方块组成.在入射电磁场的作用下,介质棒中直接被入射电磁场激励的米氏电谐振通过相互耦合作用激发了介质方块中的磁共振,并产生谐振模之间的相消干涉,从而产生了类电磁诱导透明现象.利用电磁仿真软件和双谐振子耦合模理论,模拟计算和定量分析了类电磁诱导透明效应,结果表明:在电磁波正入射下,该结构在0.552THz处产生一透射率接近96%的透明窗口.由于其结构单元具有4度旋转对称性和多个暗模谐振元素,使得诱导透明效应出现较宽频带且呈现出对入射电场极化方向不敏感的特性.     

基于群论的晶格扰动介质纳米孔阵列多重Fano共振机理及演变

基于全介质超构材料独特的电磁属性,提出了一种晶格扰动介质纳米孔阵列超构表面来激发近红外区域的多重Fano共振.结合群论深入探究了该超构表面在其原胞为方形晶格构型与方形晶格对称性被破坏两情况下多重Fano共振的形成机理及演变规律.研究表明,在方形晶格超构表面中,外部辐射连续体分别与由正入射平面波直接激发的双重简并模式共振干涉形成双重Fano共振,且该共振与原胞中是否含孔及孔的形状无关,在晶格扰动超构表面中,原本不耦合的非简并模式由正入射平面波激发出来并与外部辐射连续体干涉形成Q值更高的三重Fano共振.进一步探讨了正入射平面波的xy极化方向对上述五重Fano共振的影响,结果表明,双重简并模式Fano共振偏振无关,三重非简并模式Fano共振偏振依赖.本文将为利用方形晶格构型的超构表面实现多重Fano共振的激发及演变提供有效的理论参考.     

基于双电介质层的棱镜表面等离子共振传感的研究

为了提高表面等离子共振系统的分辨率,提出了一种五层结构的表面等离子共振效应的激励模型:棱镜基底-银膜-电介质层1-电介质层2-待测介质.采用薄膜光学和波导理论,讨论了银和双电介质层复合而成的共振薄膜对表面等离子共振效应的激励机理与调制特性的作用.借助有限元分析方法,数值模拟得到双电介质表面等离子共振激励模型的共振光谱.分析结果表明,当待测介质折射率相同时,双电介质表面等离子共振激励模型共振光谱的半峰宽约为传统棱镜表面等离子体共振的0.1倍,理论计算得到双电介质表面等离子共振激励模型的系统分辨率相较于传统棱镜表面提高了5.4倍.以乙二醇溶液为待测样本,分析得到传感器的灵敏度约为7.2°/RIU,品质因数约为465,证明了该结构设计的可行性,为设计高分辨率和高品质因数的传感系统提供了理论参考.     

光学-射频双光子耦合作用下的电磁诱导透明和电磁诱导吸收

在通常的Λ型三能级系统中,光学耦合场和探测场分别激发两个不同的光学跃迁,探测吸收谱呈现电磁诱导透明(EIT)特性.若将此系统拓展为光学-射频双光子耦合场和探测场共同作用下的准Λ型四能级系统,探测吸收谱呈现电磁诱导吸收(EIA)和EIT两种特性.通过求解系统的密度矩阵方程,分析了EIA和EIT的产生条件,并给出了相应的缀饰态解释.研究结果表明,在准Λ型四能级系统中,光学耦合场对EIA和EIT的形成起决定作用,共振时出现EIA,非共振时出现EIT,而且EIA和EIT的线宽随着光学耦合场拉比频率的增大而增加. 关键词： 电磁诱导透明 电磁诱导吸收 射频场 光学耦合场     

类氖氙离子LMn双电子复合模拟谱

在双电子复合过程发生的能量范围内,发射X光子的原子过程除双电子复合过程外还有辐射复合、共振激发、共振复合以及直接激发原子过程.本文使用相对论组态相互作用方法计算了这些过程的截面,比较了在双电子复合过程发生的能量范围内这些原子过程的截面与双电子复合过程截面,探讨了这些过程对双电子复合过程的影响.研究结果表明,辐射复合截面随入射电子束能量的增大迅速减小,在双电子复合能量范围内几乎为一常数,可以作为本底来处理;共振激发和共振复合过程对双电子复合过程的影响可以忽略不计;当入射电子束能量高于靶离子的第一激发能时,电子碰撞直接激发截面与高Rydberg态的截面连成一片,随着入射电子束能量的增加,电子碰撞直接激发截面越来越大,这时必须考虑直接激发过程.使用相对论组态相互作用方法计算了类氖氙离子的双电子复合截面,其结果与已有的部分实验和理论结果很吻合.     

类氖氙离子LMn双电子复合模拟谱

在双电子复合过程发生的能量范围内,发射X光子的原子过程除双电子复合过程外还有辐射复合、共振激发、共振复合以及直接激发原子过程. 本文使用相对论组态相互作用方法计算了这些过程的截面,比较了在双电子复合过程发生的能量范围内这些原子过程的截面与双电子复合过程截面,探讨了这些过程对双电子复合过程的影响. 研究结果表明,辐射复合截面随入射电子束能量的增大迅速减小,在双电子复合能量范围内几乎为一常数,可以作为本底来处理;共振激发和共振复合过程对双电子复合过程的影响可以忽略不计;当入射电子束能量高于靶离子的第一激发能时,电子碰撞直接激发截面与高Rydberg态的截面连成一片,随着入射电子束能量的增加,电子碰撞直接激发截面越来越大,这时必须考虑直接激发过程. 使用相对论组态相互作用方法计算了类氖氙离子的双电子复合截面,其结果与已有的部分实验和理论结果很吻合.     

Exploring electromagnetic response of tellurium dielectric resonator metamaterial at the infrared wavelengths

We numerically investigate the electromagnetic properties of tellurium dielectric resonator metamaterial at the infrared wavelengths. The transmission spectra, effective permittivity and permeability of the periodic tellurium metamaterial structure are investigated in detail. The linewidth of the structure in the direction of magnetic field W x has effects on the position and strength of the electric resonance and magnetic resonance modes. With appropriately optimizing the geometric dimensions of the designed structure, the proposed tellurium metamaterial structure can provide electric resonance mode and high order magnetic resonance mode in the same frequency band. This would be helpful to analyze and design low-loss negative refraction index metamaterials at the infrared wavelengths.     

Higher-order optical resonance node detection of integrated disk microresonator

We have demonstrated higher-order optical resonance node detection by using an integrated disk microresonator from through port of the coupling bus waveguide. In addition to the fundamental mode, the disk resonator has higher-order whispering gallery modes. The excited second-order higher-order mode has a node at the position where the electromagnetic energy of the fundamental mode is close to a maximum. This high resolution measurement of optical resonance mode profile has a variety of applications for optical sensing and detection. The self-referencing characteristics of the two optical resonance modes have potential to achieve optical detection independent of external perturbation, such as temperature change.     

Electric and magnetic dipole couplings in split ring resonator metamaterials

In this paper, the electric and the magnetic dipole couplings between the outer and the inner rings of a single split ring resonator (SRR) are investigated. We numerically demonstrate that the magnetic resonance frequency can be substantially modified by changing the couplings of the electric and magnetic dipoles, and give a theoretical expression of the magnetic resonance frequency. The results in this work are expected to be conducive to a deeper understanding of the SRR and other similar metamaterials, and provide new guidance for complex metamaterials design with a tailored electromagnetic response.     

Electromagnetic characteristics of Hilbert curve-based metamaterials

As the typical building blocks of metamaterials, the cut wire and the split ring resonator have been extensively studied in recent years. Besides them, the space-filling curve-based metamaterials are receiving great attentions because of their intrinsic subwavelength and multi-bands characteristics. In this work, we have investigated experimentally and numerically the electromagnetic characteristics of such Hilbert curve metamaterial in the microwave frequency regime and found a deeply subwavelength magnetic resonance supported by the fractal pattern and featuring the wavelength-to-size ratio more than 20. The subwavelength electromagnetic properties of the Hilbert curve will be beneficial to realize high-performance metamaterials.     

Electrothermal automodulation in incipient ferroelectric whispering-gallery microwave resonators at 4.2 K

Threshold conditions for electrothermal automodulation instability in high-Q ferroelectric microwave cryogenic resonators operating in the two-mode regime are investigated. The dependence of the electrothermal automodulation frequency on the numbers of interacting modes for different combinations of thermal modes and surface electromagnetic whispering-gallery modes is presented. The threshold power exciting the electrothermal automodulation of the oscillation of the partial mode electromagnetic amplitudes is compared with the threshold power of strictional parametric excitation of acoustic oscillations in the resonator. It is shown that the electrothermal automodulation in the two-mode regime may take place at an excitation power from 10 to 120 μW depending on the combination of interacting thermal and electromagnetic surface modes. Calculated threshold powers are low, which makes it possible to apply the electrothermal automodulation for improving the sensitivity of resonance bolometers and distributed microwave antennas with basic elements built around nonlinear microwave resonators. In addition, the electrothermal automodulation could be applied in developing novel microwave metamaterials. Nonlinear microwave whispering-gallery cryogenic resonators can be used as elements increasing the sensitivity of EPR spectroscopy methods.     

Meta材料谐振行为的因果性研究

分析了横电磁波作用下开口谐振环双各向异性Meta材料,揭示了虚波数引起Meta材料谐振行为的事实.利用Floquet模将开口谐振环周期性结构的场分布展开,从电磁波传播角度得出了凋落模是引起Meta材料谐振行为的原因.对于来自主平面上的入射波,具有相同极化方式的Floquet透射模将发生谐振,并且电谐振和磁谐振将随着入射角的不同而改变.     

异向介质谐振响应的Floquet模分析

将开口谐振环单元的场分布利用Floquet模展开,从电磁波传播角度揭示了凋落模引起异向介质谐振响应的事实.数值计算了任意平面电磁波照射下异向介质的传输特性.研究表明,对于来自主平面上的垂直或平行极化的入射波,具有相同极化方式的Floquet透射模将发生谐振,并且磁谐振和电谐振将随着入射角的不同而改变.而对于来自其他入射平面的电磁波,两种极化的Floquet透射模将共同发生谐振. 关键词： 开口谐振环 异向介质 Floquet模 谐振     

Achieving a multi-band metamaterial perfect absorber via a hexagonal ring dielectric resonator

A multi-band absorber composed of high-permittivity hexagonal ring dielectric resonators and a metallic ground plate is designed in the microwave band.Near-unity absorptions around 9.785 GHz,11.525 GHz,and 12.37 GHz are observed for this metamaterial absorber.The dielectric hexagonal ring resonator is made of microwave ceramics with high permittivity and low loss.The mechanism for the near-unity absorption is investigated via the dielectric resonator theory.It is found that the absorption results from electric and magnetic resonances where enhanced electromagnetic fields are excited inside the dielectric resonator.In addition,the resonance modes of the hexagonal resonator are similar to those of standard rectangle resonators and can be used for analyzing hexagonal absorbers.Our work provides a new research method as well as a solid foundation for designing and analyzing dielectric metamaterial absorbers with complex shapes.     

Plasmon-induced transparency effect in hybrid terahertz metamaterials with active control and multi-dark modes

We numerically demonstrate a photo-excited plasmon-induced transparency (PIT) effect in hybrid terahertz (THz) metamaterials. The proposed metamaterials are regular arrays of hybrid unit cells composed of a metallic cut wire and four metallic split-ring resonators (SRRs) whose gaps are filled with photosensitive semiconductor gallium arsenide (GaAs) patches. We simulate the PIT effect controlled by external infrared light intensity to change the conductivity of GaAs. In the absence of photo excitation, the conductivity of GaAs is 0, thus the SRR gaps are disconnected, and the PIT effect is not observed since the dark resonator (supported by the hybrid SRRs) cannot be stimulated. When the conductivity of GaAs is increased via photo excitation, the conductivity of GaAs can increase rapidly from 0 S/m to 1×10⁶ S/m and GaAs can connect the metal aluminum SRR gaps, and the dark resonator is excited through coupling with the bright resonator (supported by the cut wire), which leads to the PIT effect. Therefore, the PIT effect can be dynamically tuned between the on and off states by controlling the intensity of the external infrared light. We also discuss couplings between one bright mode (CW) and several dark modes (SRRs) with different sizes. The interference analytically described by the coupled Lorentz oscillator model elucidates the coupling mechanism between one bright mode and two dark modes. The phenomenon can be considered the result of linear superposition of the coupling between the bright mode and each dark mode. The proposed metamaterials are promising for application in the fields of THz communications, optical storage, optical display, and imaging.