类特异材料半导体复合结构中的电子Tamm态

通过选取具有特殊能带结构的半导体材料碲镉汞(Hg_1-xCd_xTe), 类比电磁体系得到了电子体系中的类单负材料、类双负材料等类特异材料, 然后将其组合成一维复合异质结构. 通过数值计算, 发现复合结构中存在新型电子Tamm态, 包括返向电子Tamm态和含类近零折射率材料复合结构中的电子Tamm态. 这些结果拓展了人们对电子Tamm态的认识.     

Surface-wave mechanism of subwavelength imaging by a flat left-handed superlens

We develop a theory describing the dynamics and interaction of electromagnetic surface waves (ESWs) resonantly excited by an external source in a slab of left-handed material (LHM) with identical negative (equal to −1) values of dielectric permittivity and magnetic permeability that makes up a so-called perfect lens, or a superlens. We show that subwavelength imaging by a superlens is associated with the degeneracy of the spectrum of eigen electromagnetic surface modes at the interfaces of the metamaterial slab, whereas the dynamic response of the superlens is completely determined by the dynamics of these modes and the dispersion properties of the metamaterial. We obtain conditions that enable one to find out when a superlens produces subwavelength images of an external source. We consider the cases of a stationary and a pulse source, as well as of a source that moves with constant velocity or oscillates in space.     

Omnidirectional reflection from the one-dimensional photonic crystal containing anisotropic left-handed material

We study the transmission properties in the one-dimensional photonic crystal containing alternate anisotropic left-handed material (LHM) layers and regular isotropic right-handed material (RHM) layers. For such an anisotropic case, the dispersion relation from the Bloch theorem is derived and the Bragg gaps of the periodic structure are observed. It is found that in the m=0 Bragg gap, there is an omnidirectionally reflectional (ODR) region, which is also invariant with a change of scale length, similar with the [`(n)]=0\bar{n}=0 gap in isotropic one-dimensional photonic crystal. With the aid of effective medium theory (EMT), the analytic expressions of all six elements of the effective electric permittivity tensor and magnetic permeability tensor are obtained. By using these results, we investigate the ODR region in the m=0 Bragg gap in all the possible cases of both TE and TM modes. We find that with different choices of parameters, the m=0 Bragg gap has different transmission properties, and the ODR region in it changes, consequently. The edges of the ODR region are given out in these cases. To one's interest, these results predict a complete reflection region in the m=0 Bragg gap, which is able to omnidirectionally reflect waves in both TE and TM modes.     

Propagation of p-polarized light in photonic crystal for sensor application

In this work, a comprehensive analytical study is presented on two-layer one- dimensional photonic crystal in which the first layer is considered to be an analyte layer and the second layer is assumed be left-handed material (LHM), dielectric or metal. The dispersion relation is derived for p- polarized wave (TM). The sensitivity of the effective index to any change in the analyte index is derived, plotted and analyzed. Our optimization shows that it is possible for photonic crystal sensor to achieve a sensitivity improvement of 714% compared to conventional waveguide sensor.     

Back-propagating surface polaritons of a one-dimensional photonic crystal containing single negative metamaterials

The existence of the surface polaritons at the interface separating a semi-infinite uniform left-handed metamaterial and a one-dimensional photonic crystal composed of alternating layers of two kinds of single-negative materials is theoretically investigated. The dispersion characteristics of the surface polaritons are analyzed and demonstrated that in the presence of metamaterial, the surface polaritons are sensitive to light polarization, so that there exist only backward TM-polarized (or TE-polarized) kind of the surface polaritons depending on the ratio of the thicknesses of the two periodic stacking layers. The existence regions of the surface polariton modes are determined for both TM-polarized and TE-polarized surface polariton modes.     

Tamm states and nonlinear surface modes in photonic crystals

We predict the existence of surface gap modes, known as Tamm states for electronic systems, in truncated photonic crystals formed by two types of dielectric rods. We investigate the energy threshold, dispersion, and modal symmetries of the surface modes, and also demonstrate the existence and tunability of nonlinear Tamm states in binary photonic crystals with nonlinear response.     

（3＋1）-dimensional nonlinear propagation equation for ultrashort pulsed beam in left-handed material

In this paper a comprehensive framework for treating the nonlinear propagation of ultrashort pulse in metamaterial with dispersive dielectric susceptibility and magnetic permeability is presented. Under the slowly-evolving-wave approximation, a generalized （3＋1）-dimensional wave equation first order in the propagation coordinate and suitable for both right-handed material （I~HM） and left-handed material （LHM） is derived. By the commonly used Drude dispersive model for LHM, a （3＋1）-dimensional nonlinear Schrodinger equation describing ultrashort pulsed beam propagation in LHM is obtained, and its difference from that for conventional RHM is discussed. Particularly, the self-steeping effect of ultrashort pulse is found to be anomalous in LHM.     

含左手材料光纤的表面模特性

在弱导条件下,利用Maxwell方程组,对纤芯是左手材料,包层是右手材料的光纤表面模进行了研究,得到了TE (TM)、 EH和 HE表面模的色散方程,.根据色散方程,画出了相应表面模和含左手材料光纤导模的色散曲线.比较这些色散曲线,发现了含左手材料光纤表面模一些新的特性.     

左手介质矩形波导的吸收特性

采用微扰法研究了左手介质矩形波导的吸收特性。由于色散方程的限制,左手介质波导不能传输基模,它的吸收特性也与右手介质矩形波导明显不同。结果发现, 模式的衰减系数随长宽比(a/b)的增加而减小,而在右手介质波导中结果恰恰相反。除此之外,当不同模式的光波在同一左手介质矩形波导中传输时,每一模式都对应着相邻很近的吸收峰和吸收谷。同时高阶模的衰减系数较低阶模的大。但是,当不同模式的光波在同一右手介质矩形波导中传输时,它们的衰减曲线随着波导宽度的增加而振荡的变化,并且趋近于芯层衰减系数。另外一方面,在右手波导中,高阶模式的衰减系数较低阶模式小。     

关于左手性介质几何光学的研究(二)

利用几何光学方法研究了由左手性介质制成的简单透镜的光学特性.推理分析了左手性介质透镜处球形界面的负折射规律,并依此表明了常用光学公式仍适用于左手性介质.指出了左手性介质透镜相对于用传统介质制作的普通透镜所具备的固有优点,最后证实了利用单块左手性介质透镜即可完全消球差,并相应提供了零球差左手性介质透镜的设计实例.     

Ternary photonic crystal with left-handed material layer for refractometric application

A ternary photonic crystal with left-handed material (LHM) layer is examined for refractometric applications. One of the layers is assumed to be air and treated as an analyte. The transmittance from the ternary photonic crystal is studied in details and the wavelength shift due to the change in the refractive index of the analyte is investigated. The transmittance is investigated with the parameters of the LHM. It is found that the wavelength shift can be significantly enhanced with the decrease of both real part of the LHM permittivity and thickness.     

Left-handed metamaterial based superlens for subwavelength imaging of electromagnetic waves

Lenses made of negative index materials have the ability to focus the propagating and evanescent components of electromagnetic waves. Such a possibility enables super resolution, in turn resulting in sharper, subwavelength size images. In this present work, we present subwavelength imaging that was obtained from a one-dimensional left-handed metamaterial (LHM) composed of alternating layers of split-ring resonators and thin wires. We investigated the effect of the thickness of LHM lenses on image size. The left-handed pass band within the negative permittivity and permeability region is shown experimentally and theoretically for different thicknesses of LHM slabs. We also studied the transmission-phase of LHMs with a different number of unit cells along the propagation direction. The phase decreases with the increasing thicknesses of LHM slabs, proving that the phase velocity is negative in the left-handed transmission band. PACS 42.25.-p; 41.20.Jb; 81.05.-t     

关于左手性介质几何光学的研究(一)

根据几何光学中的费马原理和完善成像原理研究了光线经过正负折射率界面时的传播特性,推导了单负折射率完善成像的曲面方程,讨论了单块负折射率透镜成像特性的一些缺陷及改进方案,依此指出了最短时间原理的适用范围的局限性和利用左手性介质制作光学器件的优越性,为进一步研究左手性介质的光学特性和相关光学器件设计提供了理论基础.     

Multi-band terahertz two-handed metamaterial based on the combined ring and cross pairs

We present the design of a Multiband two-handed metamaterial (MM) with the composite structure combined ring and cross pairs (RP + CP) in the terahertz regime. The dual-band left-handed and single-band right-handed transmission properties of this composite structure were explored by the FDTD method. The MM exhibits left-handed and right-handed transmission pass bands around the frequencies of 0.43 THz, 1.32 THz and 0.85 THz for the terahertz electromagnetic (EM) wave normal incidence, respectively. The surface currents distributions are demonstrated to discuss the physical mechanism of the left-handed properties of the proposed MM. The retrieved equivalent EM parameters and the refraction phenomenon based on a wedge-shaped model verify the left-handed properties. Furthermore, the dual-band left-handed transmission properties of RP + CP structure can be tunable individually by changing the structural parameters. The presented design of terahertz two-handed MM offers a flexibility for investigation of their novel EM properties, and important terahertz device applications.     

基于蘑菇型结构的双入射超宽带复合媒质材料设计与分析

通过设计一定的单元结构, 可以实现超宽带人工电磁材料. 基于蘑菇型金属结构, 提出了一种同时具有左右手通带无缝结合的超宽带双入射型复合媒质材料结构单元. 该结构由嵌入到介质板的两个反向对称的蘑菇型金属结构组成, 能够同时引发电谐振和磁谐振而得到左手通带. 通过利用CST软件仿真、等效电磁参数提取、折射率计算以及建立等效磁谐振电路模型等方法, 分析验证了该结构的双入射特性和左手特性. 仿真结果表明, 在电磁波垂直于介质板和平行于介质板入射两种情况下, 在X波段均表现出左手通带特性, 并具有1 GHz以上的左手带宽. 当电磁波垂直于介质板入射时, 在7.2 GHz-9.3 GHz频段为右手通带, 在9.3 GHz-11 GHz频段为左手通带; 当电磁波平行于介质板入射时, 在7.0 GHz-9.0 GHz频段为右手通带, 在9.0 GHz-10 GHz频段为左手通带. 在两种情况下分别于9.3 GHz与9.0 GHz处得到了零折射率, 从而构造了一种正-零-负复合媒质材料, 实现了具有3 GHz带宽的双入射超宽带平衡结构.     

Nonlinear Tamm states in layered metal–dielectric metamaterials

We study nonlinear surface modes at the edge of metal–dielectric nanostructured metamaterial with a nonlinear surface layer. We demonstrate that such semi‐infinite structures can support transverse electric (TE) polarized surface states with subwavelength localization near the surface, an optical analogue of the Tamm states, even in the cases when the surface modes do not exist in the linear regime. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical Tamm states at the interface between a photonic crystal and a nanocomposite with resonance dispersion

Optical Tamm states localized at the edges of a photonic crystal bounded from one or both sides by a nanocomposite have been studied. The nanocomposite consists of metallic nanoinclusions, which have a spherical or orientationally ordered spheroidal shape and are dispersed in a transparent matrix, and is characterized by the resonant effective permittivity. The transmission, reflection, and absorption spectra have been calculated for waves with longitudinal and transverse polarizations in such structures at the normal incidence of light. The spectral manifestation of Tamm states that is due to the existence of negative values of the real part of the effective permittivity has been analyzed for the visible spectral range. It has been established that the characteristics of Tamm states localized at the edge of the photonic crystal depend strongly both on the concentration of nanoballs in the nanocomposite film and on its thickness. Modes formed by two coupled Tamm plasmon polaritons localized at the edges of the photonic crystal adjacent to two nanocomposite layers have been examined. It has been shown that, in the case of the anisotropic nanocomposite layer adjacent to the photonic crystal, each of two orthogonal polarizations of the incident wave corresponds to a specific frequency of the Tamm state localized at the edge; owing to this property, the transmission spectra of such a structure are polarization sensitive.     

左手系材料界面上的非线性TE电磁波

针对电磁波在非线性左手系材料中的传播性质, 分别研究了左、右手系材料界面以及两左手系材料界面上非线性TE表面波的传播行为讨论了导波的频率特性、色散关系以及群速度随频率的变化规律分析表明,两种界面上的非线性TE表面波均存在频率通带和禁带,且带宽是传播功率的函数揭示了在一定条件下,左、右手系材料界面上既可以支持正向传播的非线性TE表面波,也可以支持反向传播的非线性TE表面波;两左手系材料界面上表面波的传播性质因材料参量的变化差异较大,一定参量条件下,该界面上仅支持反向传播的非线性TE表面波.     

含奇异材料的掺杂一维光子晶体色散关系和空间局域度理论

给出了描述掺杂的一维光子晶体结构缺陷态的变化规律及其空间局域度特性的理论表达式.该式对由具有任意色散关系材料组成的、中间掺杂、两边对称的一维光子晶体结构均成立.通过研究含奇异材料的光子晶体组态发现，当缺陷层材料为右手材料时，光子带隙中缺陷态的频移方向随缺陷层厚度的增大而红移；当缺陷层材料是左手材料时，频移方向刚好相反，表现为蓝移.该缺陷态的空间局域度只与两边对称结构有关.两边对称结构含奇异材料的光子晶体的缺陷态比传统右手材料的结构具有更强的空间局域度.     

Controlled switching of surface waves in 1D photonic crystals by a thin nonlinear cap layer

In this paper, we investigate the electromagnetic surface waves localized at the interface of the homogeneous dielectric medium and a semi-infinite one-dimensional photonic crystal (1D PC), theoretically. The semi-infinite 1D PC is made of alternative layers of left-handed (LH) and right-handed (RH) materials in the presence of a thin nonlinear cap layer. We consider magnetic permeability and electric permittivity of LH layers being dispersive and non-dispersive. We used an analytical direct matching procedure within the Kronig-Penny model to analyze the dispersion behavior of surface waves with controllable localization. It is shown that the thin nonlinear cap layer acts as a tool to change the backward surface waves to forward ones and vice versa and it plays an important role on the localization of them. Also we show that when the LH layers are chosen dispersive, negative dispersion of surface waves are obtained in a wide range of radiation angle and frequency, and we propose an approach to calculate the applied electric field intensity that leads to switching of surface waves from backward to forward and creating a surface mode with maximum localization.