负介电常数材料与负磁导率材料双层结构的透射特性

利用麦克斯韦方程组研究了负介电常数材料和负磁导率材料组成的双层结构的透射特性.电磁波在跨越负介电常数材料层和负磁导率材料层的界面时，由边界条件导致了电磁场的大部分能量局域在界面上，形成特殊的界面模式.研究结果表明，当入射角满足某个特定条件时，这些界面模可以演变为共振隧穿模，导致共振透射的发生.这种输运特性可以实现带通滤波. 关键词： 负介电常数材料 负磁导率材料 单负材料 带通滤波器     

异向介质材料的非线性研究进展

异向介质材料是由人工设计构造的、具有特异电磁特性的材料。其中同时具有负的介电常数ε及磁导率μ的称为左手材料或双负材料;仅有负的介电常数ε或负的磁导率口的称为单负材料。本文介绍了实现异向介质材料及其非线性特性的方法,重点综述了异向介质材料中SH产生、光孤子传输、波混频效应等方面的研究进展。     

异向介质材料的非线性研究进展

异向介质材料是由人工设计构造的、具有特异电磁特性的材料。其中同时具有负的介电常数ε及磁导率μ的称为左手材料或双负材料;仅有负的介电常数ε或负的磁导率μ的称为单负材料。本文介绍了实现异向介质材料及其非线性特性的方法,重点综述了异向介质材料中SH产生、光孤子传输、波混频效应等方面的研究进展。     

含单负材料三明治结构的电磁隧穿特性

在理论分析的基础上,结合实验研究了单负材料/正折射率材料(或单负材料)/单负材料三明治结构的电磁隧穿性质.这种结构的电磁隧穿来源于入射平面波与结构的表面或体极化激元的耦合,从理论上讨论并计算了正入射情况下这种结构中的极化激元的色散关系.发现:由单负材料作为边界而正折射率材料为中间层的三明治结构具有体极化激元,这种极化激元的共振频率随着中间层厚度的增加向低频移动;由不同性质的单负材料构成的三明治结构具有两条色散曲线,这两条色散曲线随着中间层厚度的增加而简并.随后基于L-C传输线技 关键词： 单负材料 极化激元 隧穿 L-C传输线')" href="#">L-C传输线     

负介电常数材料和负磁导率材料的双层结构中电磁波模式分析

研究了双层单负材料结构中电磁波的模式,主要分析了不同模式的产生条件,讨论了这些模式与材料参数之间的关系.当材料参数满足平均介电常数和磁导率为零时出现隧穿模式.当满足波导模产生条件时,波导模式的电磁波在材料两边的半无限真空中以消逝波存在,在双层单负材料的界面处也可以出现较强的局域场. 关键词： 单负材料 传播模式 隧穿模式 波导模式     

负介电常数材料和负磁导率材料的双层结构中电磁波模式分析

研究了双层单负材料结构中电磁波的模式,主要分析了不同模式的产生条件,讨论了这些模式与材料参数之间的关系.当材料参数满足平均介电常数和磁导率为零时出现隧穿模式.当满足波导模产生条件时,波导模式的电磁波在材料两边的半无限真空中以消逝波存在,在双层单负材料的界面处也可以出现较强的局域场.     

基于传输线的单负材料双层结构的隧穿性质

通过传输线方法实现了负介电常数(ENG)和负磁导率(MNG)材料,并在实验上研究了由两种单负材料组成的双层结构(ENG-MNG)的电磁隧穿性质.结果表明,两种单负材料均不支持电磁波的传播,然而ENG-MNG双层结构在结构的平均介电常数和平均磁导率分别为零的条件下,具有完全隧穿模,并且这一隧穿模不随着结构尺度的改变而改变.在隧穿频率点,通过对ENG-MNG双层结构中电场分布的模拟与测量,实验上观察到了倏逝场的指数放大.     

三层单负材料结构中电磁波模分析

本文分析了由负介电常数材料和负磁导率材料交替排列组成的一维三层结构中的电磁波模式,包括传播模及波导模.传播模对应于入射的行波模,着重研究了发生共振隧穿时场分布和透射谱随入射角度的变化关系,发现改变结构参数时共振隧穿频率会劈裂成两个,且这两个隧穿模的频率间距随着中间层厚度的减小而逐渐加大.波导模是指在结构两边的半无限真空中以倏逝场形式存在的电磁模式,分析了它的存在条件即色散关系,发现这种模在材料的交界面处会出现较强的局域场. 关键词： 单负材料 共振隧穿 传播模 波导模     

利用含负折射率材料的光子晶体实现角度滤波器

利用光子晶体的共振隧穿效应，并结合由负折射材料引起的零平均折射率带隙，设计出一种新型的角度滤波器，使得对于某一频率范围内的入射电磁波仅在特定入射角度的波能够全透，而其他角度的波不能透过.这将在微波器件乃至光学器件上有广泛应用. 关键词： 光子晶体 负折射率材料 共振隧穿     

含单负介质层受阻全内反射结构的光子隧穿现象研究

利用稳定相位理论得到了光子穿越含单负介质层受阻全内反射结构的隧穿时间以及光子穿透光学势垒后产生的横向位移.分析结果表明，当势垒为单负介质时，光子隧穿可能表现出负的隧穿时间和负的横向位移.隧穿时间和横向位移存在Hartman效应，使得光子隧穿过程具有超光速性质.此外，基于TM波和TE波通过负介电常数介质和负磁导率介质势垒产生的横向位移的方向正好相反，得到了一种有效的区分两类单负介质的方法. 关键词： 光子隧穿 负折射 单负介质 超光速     

Comparison of tunneling times in isotropic and anisotropic media

We present a comparative analysis of the tunneling times of electromagnetic (EM) waves propagating in isotropic and anisotropic media. First, suitable expressions for the tunneling times in a layered periodic material, with anisotropic properties originating from its structure, are derived, followed by numerical calculations performed for a new type of anisotropic semiconductor metamaterial. In the first case, we have considered a layered structure which contains two differently doped In_0.53Ga_0.47As semiconductor layers. The second structure under investigation is made of alternately placed layers of doped In_0.53Ga_0.47As and undoped Al_0.48Ga_0.52As. The investigation of the dwell time as a function of incident wave frequency has revealed the existence of two peaks, one of which may be interpreted as a consequence of anisotropy, while the other one corresponds to the peak related to the absorption and the group delay. Both of these two peaks are affected by variations of layers?? doping densities. Furthermore, at increased incident angles of incoming EM waves, the dwell time peak occurs at the upper boundary of the frequency interval, for which the structure exhibits negative refractive index.     

基于双粒子耦合的单层介质柱阵列对电磁波的调控

基于Mie散射理论和多重散射理论探讨了亚波长介质柱阵列对电磁波的调控. 研究结果表明: 当在全反射的单层介质柱阵列中引入一个空位缺陷时会产生12%的透射; 如果在入射一侧再引入一合适的介质柱时, 其透射率可增加至36%, 为空位缺陷时的3倍; 当在出射一侧对称位置处引入另一完全相同的介质柱时, 可以调制透射电磁波的模式, 虽然总的透射率没有增加,但向前散射的电磁波能量明显增强. 采用这种双粒子耦合体系, 在金属柱的表面等离激元共振频率附近也可以实现类似的效果. 这些体系结构简单、易于在实验上实现, 这对于太赫兹甚至光频段的光子集成线路中的元件设计和光束调控很有意义.     

Controlling the phase delay of light transmitted through double-layer metallic subwavelength slit arrays

We demonstrate that the phase of light transmitted through double-layer subwavelength metallic slit arrays can be controlled through lateral shift of the two layers. Our samples consist of two aluminum layers, each of which contains an array of subwavelength slits. The two layers are placed in sufficient proximity to allow coupling of the evanescent fields at resonance. By changing the lateral shift between the layers from zero to half the period, the phase of the transmitted electromagnetic field is increased by pi, while the transmitted intensity remains high. Such a controllable phase delay could open new capabilities for nanophotonic devices that cannot be achieved with single-layer structures.     

Plasmonic planar lens based on stack of metal–insulator–metal waveguides with height tuning

We introduce a technique capable of focusing electromagnetic (EM) waves through plasmonic nanoslits symmetrically arranged along the indented semi-circular surface in silver background. The EM transports through the tuning slits in the form of surface plasmon polaritons (SPPs), and gets the required phase retardations to focus at the focal plane. Due to the subwavelength nature of planar metallic lens, we present the rigorous electromagnetic analysis by using two dimensional (2D) finite difference time domain (FDTD) method. These height-modulated slits with uniform width are demonstrated to have unique advantages in beam manipulation. In combination with previous studies, it is expected that our structure with small number of slits could lead to realization of optimum designs of plasmonic nano-lens.     

Electromagnetic tunneling through conjugated single-negative metamaterial pairs and double-positive layer with high-magnetic fields

We show that resonant tunneling of electromagnetic （EM） fields can occur through a six-layer structure con- sisting of two pairs of bilayer slabs： one＇being an epsilon-negative layer and the other being a mu-negative layer with a double-positive （DPS） medium and air. This type of tunneling is accompanied by high-magnetic field. The Poynting vector distributions and the material dissipation are studied. Our results demonstrate that the EM field in the structure is controlled flexibly by single-negative media and DPS slab. Therefore, this structure has potential applications in wireless energy transfer.     

Surface plasmon-polaritons wave fields in the vicinity of a metallic nanohole

It is shown that metal surface with a nanohole can support surface plasmon-polaritons (SPP), whose wave fields are described by Hankel functions. These plasmons can be excited by an electromagnetic wave incident at the metal surface. The optical transmission through subwavelength holes in metal films can essentially be enhanced by interaction of the incident light with surface plasmons. Dependence of excitation of the wave field of SPP on the incidence angle and on the wavelength of incident light is considered.     

Transmission through array of subwavelength metallic slits curved with a single step or mutli-step

The transmission of normally incident plane wave through an array of subwavelength metallic slits curved with a sin- gle step or mutli-step has been explored theoretically. The transmission spectrum is simulated by using the finite-difference time-domain method. The influences of surface plasmon polaritons make the end of finite long sub-wavelength metallic slit behaves as magnetic-reflecting barrier. The electromagnetic fields in the subwavelength metallic slits are the superpo- sition of standing wave and traveling wave. The standing electromagnetic oscillation behaves like LC oscillating circuit to decide the resonance wavelength. Therefore, the parameters of adding step may change the LC circuit and influence the transmission wavelength. A new explanation model is proposed in which the resonant wavelength is decided by four factors： the changed length for electric field, the changed length for magnetic field, the effective coefficient of capacitance, and the effective coefficient of inductance. The effect of adding step is presented to analyze the interaction of two steps in slit with mutli-step. This explanation model has been proved by the transmission through arrayed subwavelength metallic slits curved with two steps and fractal steps. All calculated results are well explained by our proposed model.     

Magnetoelectric Energy in Electrodynamics: Magnetoelectricity,Bi(an)isotropy,and Magnetoelectric Meta-Atoms

Magnetoelectricity denotes the relationship between electric polarization and magnetization. In materials with an intrinsic magnetoelectric (ME) effect, the energy density comprises the polarization, magnetization, and ME energy densities. These three components of energy define local (subwavelength) characteristics of electromagnetic (EM) responses in multiferroic materials. In a subwavelength domain, coupling between the electric and magnetic dipole oscillations forms the ME field structures that are characterized by the violation of both spatial and temporal symmetry. Unlike multiferroics, bi(an)isotropic metamaterials are associated with an EM response characterized only by spatial symmetry breaking. This also applies to chiral materials. Since no “intrinsic magnetoelectricity” is assumed in such structures, any concepts about the stored ME energy are not applicable. This clearly points to the effect of nonlocality. That is why the basic concepts of bi(an)isotropy can only be analyzed by the EM far-field characteristics. In this paper, it is argued that in the implementation of local (subwavelength) ME meta-atoms and systems for near-field probing of chirality, the concept on ME energy is crucial. Real ME energy can occur when ME fields in a singular subwavelength domain are characterized by a violation of both the symmetry of time reversal and spatial reflection.     

Reflection and transmission of strongly focused vector beams at a dielectric interface

The reflection and transmission of tightly focused azimuthally and linearly polarized electromagnetic wave beams with subwavelength spot size at a dielectric interface are investigated. A substantial increase of the reflectance of a light beam that is normally incident from a higher-index medium to a lower-index medium and a decrease of the reflectance of a beam that is incident from a lower-index medium to a higher-index dielectric medium in comparison with the Fresnel reflectance are predicted.     

飞秒光丝阵列对10 GHz电磁波的吸收特性

为了研究飞秒光丝阵列对10 GHz电磁波的吸收特性,建立了飞秒光丝阵列吸收电磁波的有限元模型,研究了光丝内电子温度、电子数密度、光丝直径和电磁波的极化等参数对吸收系数的影响。研究结果表明:当电磁波偏振方向与光丝轴向垂直时,阵列对电磁波是透明的;增加光丝内电子数密度或提高电子温度,吸收系数先增大后减小;当光丝直径与电磁波趋肤深度相等时,吸收系数达到最大值。对于S极化电磁波,当光丝直径为50 μm时,吸收系数随入射角的增大而变大;当光丝直径为100~200 μm时,在入射角较小时,吸收系数随入射角的增大而变大;在入射角较大时会出现吸收峰值,最高可达0.45,且光丝直径越大,吸收峰值对应的入射角就越小;对于P极化电磁波,吸收系数随入射角增大而降低。