Bright and dark spatial solitons in metallic nanowire arrays

We investigate the formation and propagation of bright and dark three-dimensional unstaggered spatial solitons with cylindrical symmetry in a nonlinear nanowire metamaterial. The metamaterial is formed by metallic nanowires embedded in a Kerr-type dielectric host and is modeled using an effective medium approach. Unlike conventional Kerr media, the metamaterial supports bright solitons when the host is a self-defocusing material and dark solitons when the host is a self-focusing material. Our numerical calculations show that the confinement of the spatial-solitons results from the interplay of the host nonlinear response strength and the hyperbolic dispersion of the photonic states in the nanowire array. Subwavelength solitary beams may be observed for sufficiently strong nonlinearities.     

Metamaterial with simultaneously negative bulk modulus and mass density

We report a metamaterial which simultaneously possesses a negative bulk modulus and mass density. This metamaterial is a zinc blende structure consisting of one fcc array of bubble-contained-water spheres (BWSs) and another relatively shifted fcc array of rubber-coated-gold spheres (RGSs) in epoxy matrix. The negative bulk modulus and mass density are simultaneously derived from the coexistent monopolar resonances from the embedded BWSs and dipolar resonances from the embedded RGSs. The Poisson ratio of the metamaterial also turns negative near the resonance frequency.     

Experimental demonstration of subwavelength focusing of electromagnetic waves by labyrinth-based two-dimensional metamaterials

We studied focusing in a two-dimensional metamaterial that was based on a labyrinth structure. We theoretically showed that the labyrinth-based metamaterial exhibits negative indices of refraction between 6 and 6.4 GHz. We experimentally studied the focusing effect by measuring electric field intensities on the output side of the metamaterial when the source was placed in front of the input side of the metamaterial. Our experimental results showed that it is in fact possible to focus the source field with half-widths as small as wavelength/4 by using the labyrinth-based metamaterial.     

Optical superradiance on cooperative transitions in metamaterials

The possibility of observing collective spontaneous emission upon a cooperative transition in an ensemble of interacting optical center pairs embedded in a metamaterial is investigated. It is shown that when the effective refractive index tends to zero, the relaxation rate of excited atomic states substantially decreases, allowing us to observe collective effects on weaker cooperative transitions.     

Doppler effects of a light source on a metamaterial slab: a rigorous Green's function approach

We apply a (rigorous) Green's function theory to study the Doppler effects of a light source placed on top of a metamaterial slab. When the receiver is in motion with the source and the slab, we find that, in addition to a conventional Doppler mode, there are several other frequency components that do not obey the standard frequency-shift rule. We show that such new effects are caused by the coupling between the radiated electromagnetic waves and the surface modes of the metamaterial slab, whose dispersion relation varies as a function of velocity in the moving reference frame.     

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.     

Dynamical Green's function theory to study the optical phenomena related to metamaterials

We combine a space–time Lorentz transformation with a dyadic Green's function technique to establish a general and rigorous dynamical theory, which can be employed to study the optical phenomena occurring in a moving environment. As the applications of this method, we studied the Doppler effects of a source moving near a metamaterial slab and the super imaging effect achieved by a moving metamaterial lens. Many interesting anomalous phenomena were discovered, induced typically by the interplays between the source and the surface waves of the metamaterial slab.     

An ultra-broadband metamaterial absorber based on the hybrid materials in the visible region

In this paper, an ultra-broadband metamaterial absorber is successfully designed in the visible region. The structure of the absorber is just obtained by the two-dimensional plane structure which rotate 90° along x-axis. Furthermore, the formation of the structure for the hybrid materials is based on the four U-shaped structure of the metal titanium is embedded in the semiconductor (indium antimonide). The simulated results show that the proposed metamaterial absorber can achieve an ultra-broadband absorption with greater than 90% from 252.2 to 822.3 THz, and the relative absorption bandwidth gets to 106.1%. Finally, the simulated electric field, surface current and power loss density distributions further illustrate the absorption mechanism of the metamaterial absorber. And we believe the metamaterial absorber will have many potential applications in energy harvesting and stealth devices.     

基于钛酸锶钡介电非线性效应的可调谐太赫兹人工电磁媒质

数值仿真研究了内嵌钛酸锶钡薄膜夹层的金属网格谐振单元人工电磁媒质的谐振行为. 垂直电磁波激励下, 电磁响应频率随着内嵌夹层钛酸锶钡薄膜介电常数的变大呈现红移, 调谐率为22.6%. 本文提出的人工电磁媒质调谐方法只需要以结构单元的上下两层金属图形本身作为电极对内嵌夹层钛酸锶钡薄膜施加电压, 极大地简化了可调谐人工电磁媒质的制备及应用, 在太赫兹人工电磁媒质调制器等方面具有潜在的应用. 关键词： 人工电磁媒质 钛酸锶钡薄膜 介电非线性 调谐     

Goos-Hänchen shift and time delay in dispersive nonlinear media

We present an analysis of the influence of the Goos-Hänchen effect on tunneling times, group delay and dwell time, of electromagnetic waves propagating through an obstacle made of left-handed metamaterial embedded in a dielectric which exhibits saturable type of nonlinearity. The derived equations show that only the group delay, is affected by the Goos-Hänchen shift without any impact on the dwell time. Besides the reduction of the group delay, the most remarkable result is the possibility for total reduction of the Goos-Hänchen shift for finite incident angles. These phenomena are observable in the frequency region for which metamaterial exhibits negative index of refraction.     

磁单负材料板附近的原子的自发辐射场分布

本文研究了磁单负材料板附近的两能级原子通过自发辐射激发的表面模式及场强分布. 磁单负材料是有效介电常数大于零而磁导率小于零的人工微结构材料. 根据麦克斯韦方程及边界条件, 这种材料板只支持TE极化的表面模式. 本文分析了具有不同磁导率和厚度的磁单负材料板所支持的表面模的性质, 如模式数目和模式的对称性, 进而讨论了这些特性对原子自发辐射场的空间分布的影响. 结果表明原子与磁单负材料板的距离可影响辐射场中表面模的比重, 当表面模起主要贡献时, 在材料板左表面上原子辐射场呈定向发射的分布. 而材料板右表面的辐射场分布取决于表面模的对称性和比重, 如果同时存在对称和反对称的表面模, 右表面的场很弱甚至完全消失, 而如果只存在对称或反对称的表面模, 右表面会有与左表面等强度的辐射场分布. 这些性质与原子在金属表面的辐射场分布明显不同, 我们的结果对原子辐射场的空间控制以及实现简单结构的单光子源有积极意义.     

Light-wave guidance through stratified photonic crystal metamaterials synthesized by superinductive layers of metallic nanostrips

The electrodynamic properties of a novel class of photonic-crystal metamaterial platform entirely synthesized by ultralow-refractive-index suspended nanostrips embedded in a dielectric matrix are described and investigated. The optical properties of the homogeneous metamaterial platform can be understood on the basis of equivalent distributed circuit extraction from an electromagnetic model that has negatively distributed superinductive properties. Low propagation loss, temperature-insensitive characteristics, and ultracompact size are the main advantages of the proposed technology, making this new type of metamaterial an excellent candidate for use in compact multilayer nanophotonic integrated systems.     

Taming the blackbody with infrared metamaterials as selective thermal emitters

In this Letter we demonstrate, for the first time, selective thermal emitters based on metamaterial perfect absorbers. We experimentally realize a narrow band midinfrared (MIR) thermal emitter. Multiple metamaterial sublattices further permit construction of a dual-band MIR emitter. By performing both emissivity and absorptivity measurements, we find that emissivity and absorptivity agree very well as predicted by Kirchhoff's law of thermal radiation. Our results directly demonstrate the great flexibility of metamaterials for tailoring blackbody emission.     

Relaxation mechanisms in three-dimensional metamaterial lens focusing

We study the transient behaviors in focusing a point source with a metamaterial lens (epsilon = mu = -1 + delta). We find the time evolutions of image formation are dictated by two relaxation mechanisms, namely, surface wave transport and absorption, determined, respectively, by Re(delta) and Im(delta). We show that image oscillations are inevitable in this three-dimensional configuration when Re(delta) double dagger 0 and establish relationships among the relaxation time, the resolution enhancement, and delta.     

Optical metamaterial absorber based on leaf-shaped cells

We present the model of an infrared metamaterial absorber composed of metallic leaf-shaped cells, dielectric substrate, and continuous metallic film. Numerical simulation confirms an absorptivity of 99.3% at the infrared frequency of 126.7 THz with this metamaterial model. The proposed metamaterial absorber could be fabricated with an electrochemical deposition technique. Our simulated results show the absorption feature of this metamaterial absorber could be well manipulated with different incident angles and radiation modes. The optical metamaterial absorber proposed in this paper has potential applications such as infrared imaging devices, thermal bolometers, wavelength-selective radiators, and optical bistable switches.     

Thermal broadband tunable Terahertz metamaterials

A thermally tunable metamaterial comprising a periodic array of metallic split-ring resonators with an embedded semiconductor has been proposed. The resonance frequencies of the metamaterial are demonstrated to be continuously tuned in the terahertz regime by increasing the temperature. The tunability is attributed to the temperature-dependent permittivity of the embedded semiconductor and well analyzed by an equivalent capacitor-inductor model. The proposed designs ensure broadband thermally tunable terahertz devices.     

Amplification of acoustic evanescent waves using metamaterial slabs

We amplified acoustic evanescent waves using metamaterial slabs with a negative effective density. For the amplifying effect of the slab to overcome the dissipation, it is necessary that the imaginary part of the effective density is much smaller than the real part, a condition not satisfied so far. We report the construction of membrane-based two-dimensional negative-density metamaterials which exhibited remarkably small dissipation. Using a slab of this metamaterial we realized a 17-fold net amplitude gain at a remote distance from the evanescent wave source. Potential applications include acoustic superlensing.     

Tunable I-shaped metamaterial by loading varactor diode for reconfigurable antenna

A tunable metamaterial by employing I-shaped metamaterial with loaded varactor diode is presented in this paper and the phase of emitting wave modulated by the varactor diode is demonstrated. We have proved that the energy loss is relatively low when the working frequency is chosen to be away from the resonance frequency of the I-shaped metamaterial. By using the metamaterial, a pattern reconfigurable antenna is designed based on arrayed antennas theory. Simulations results show that the radiation pattern can be tuned to different angles by properly arranging the linear phase difference of adjacent regions.     

Trapping of electromagnetic wave in single-negative metamaterial waveguides

We study the trapping properties of transverse magnetic (TM) waves in single-negative metamaterial waveguides including epsilon-negative (ENG) metamaterial and mu-negative (MNG) metamaterial. The relationship between effective refractive index and reduced core width is analyzed when the permittivities of ENG and MNG metamaterials are different, and the inflection on this curve can be regarded as the trapping point. Simulation results show that the properties in an ENG–MNG–ENG metamaterial waveguide are contrary to that in a MNG–ENG–MNG metamaterial waveguide. The sensitivity of trapping point to the change of permittivity makes the single-negative metamaterial waveguides to be an effective method to detect the permittivity variation and can be used as a new kind of waveguide sensor.