Hyperbolic metamaterial using chiral molecules

We theoretically investigate the intra-band transitions in Mobius molecules.Due to the weak magnetic response,the relative permittivity is significantly modified by the presence of the medium while the relative permeability is not.We show that there is hyperbolic dispersion relation induced by the intra-band transitions because one of the eigen-values of permittivity possesses a different sign from the other two,while all three eigen-values of permeability are positive.We further demonstrate that the bandwidth of negative refraction is 0.165 eV for the H-polarized incident light,which is broader than the ones for inter-band transitions by 3 orders of magnitude.Moreover,the frequency domain has been shifted from ultra-violet to visible domain.Although there is negative refraction for the E-polarized incident light,the bandwidth is much narrower and depends on the incident angle.     

Negative refraction and energy flow

The conditions for negative refraction are examined in a medium with complex permittivity and permeability. The direction of the wave is taken to be in the direction of the Poynting vector, and it is shown that the condition for negative refraction is that the real part of the permeability must be negative. PACS 41.20.Jb; 42.15.Dp     

The influence of EIT effect with double windows on electromagnetic characteristics of quasi-Λ-four-level atomic system

In this paper, the electromagnetic characteristics of quasi-Λ-four-level atomic system influenced by electromagnetically induced transparency (EIT) effect with double windows are investigated theoretically. It is shown that the permittivity can get two negative extreme values in transparent window extents and the permeability can realize negative value. Consequently, the atomic system can obtain the negative refraction in discontinuous probe detuning frequency ranges. EIT effect with double transparent windows would extend the tuning frequency range of realizing left handedness in atomic system. Furthermore, due to the strong magnetic transition, the real part of the refractive index and the absorption of atomic system can obtain negative values in the same certain frequency band. Such left-handed quasi-Λ-four-level atomic system may become an active medium.     

负折射率材料对Casimir效应的影响

研究了负折射率材料介质板间的Casimir效应.对于负折射率材料中由Drude-Lorentz型色散关系描述的介电常数和磁导率，色散曲线中负值频带的曲线结构由各色散吸收参数所决定，色散曲线负值频带宽度和负区域的深度等性质的变化影响了介质材料板的反射特性，进而对两材料板间的Casimir效应强弱起着重要的作用.     

Study of group velocity in the negative refractive index region in three level closed Λ system via spontaneously generated coherence

A new approach is suggested to realize simultaneous negative permittivity and permeability in a three level closed system with incoherent pumping via spontaneously generated coherence (SGC). In this system the negativity of the real part of magnetic permeability can be achieved in the presence of SGC whereas in the absence of SGC it is positive. Thus the SGC makes the system a negative index medium (NIM) in a band of frequency range. The position and the band of the frequency region of negative refraction can be manipulated by controlling the incoherent pump rate. We achieve FOM?=?7.91165. We have studied the group index in the negative refractive index region and have shown that the group velocity switches from superluminal to subluminal mode in this region of negative refraction. We have shown that the negative refractive index can be realized in a heteronuclear molecule.     

Negative refraction and imaging beyond the diffraction limit by a two-dimensional left-handed metamaterial

We report our experimental results on two-dimensional left-handed metamaterials (LHM) exhibiting negative refraction and subwavelength imaging. Transmission and reflection spectra of LHM are studied and a left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are negative. Impedance matching is verified both with the experiments and simulations. The two-dimensional LHM structure is verified to have a negative refractive index. We employed three different methods to observe negative refraction; refraction through prism-shaped LHM, beam shifting method, and phase shift experiments. We further demonstrated subwavelength imaging and resolution using LHM superlenses. The effect of thickness on the resolving power is investigated experimentally.     

Tunable beam splitting and negative refraction in heterostructure with metamaterial

The dispersion characteristics of one-dimensional heterostructure with metamaterial is presented. We give a theoretical analysis and numerical simulations for tunable beam splitting and negative refraction. By adjusting the lattice constant of the heterostructure or the permeability of the metamaterial, the splitting angle can be tuned. Interestingly, if both the average permittivity and permeability are zero, the splitting angle will be 180 degrees. Moreover, when the permeability of metamaterial is small enough, the light cannot propagate in the heterostructure if the incident angle is less than the critical angle. And as soon as the incident angle is larger than the critical angle, negative refraction will occur. In addition, the negative refraction can also be tuned.     

Anisotropy of electromagnetically induced left-handedness in atomic three-level media based upon bianisotropic polarizabilities and tensor character

A three-level atomic system, configured as either a gaseous medium or a solid state material, with a driving field establishing a Rabi frequency of control, is tested by a probe field. The medium has bianisotropic microscopic polarizability and magnetizability, from which the permittivity and permeability tensors are derived. Non-isotropy and polarization dependence for left-handedness (negative index of refraction) is demonstrated through examination of tensor components in the detuning frequency spectrum. These results have important implications for use in optical or electronic devices.     

New assembly route for three-dimensional metamaterials obtained through effective medium theory

In this study,we illustrate the effective medium theories in the designs of three-dimensional composite metamaterials of both negative permittivity and negative permeability.The proposed metamaterial consists of random coated spheres with sizes smaller compared to the wavelength embedded in a dielectric host.Simple design rules and formulas following the effective medium models are numerically and analytically presented.We demonstrate that the revised Maxwell-Garnett effective medium theory enables us to design three-dimensional composite metamaterials through the assembly of coated spheres which are random and much smaller than the wavelength of the light.The proposed approach allows for the precise control of the permittivity and the permeability and guides a facile,flexible,and versatile way for the fabrication of composite metamaterials.     

Negative refraction with low absorption using EIT in a four-level left-handed atomic system

We suggest a scheme for obtaining negative refraction with low absorption in a left-handed atomic system. Under the appropriate conditions, the atomic system displays negative refraction with negative permittivity and permeability (left-handedness) in a common frequency range, simultaneously. And the imaginary parts of permittivity and permeability show transparently propagate in the same frequency range. Finally, the negative refraction show low absorption due to the EIT effect, and the figure of merit demonstrated this in this resonant atomic system.     

十字环型左手材料单元结构设计与仿真

提出了一种新型十字环型左手材料结构单元.该结构只需在介质板单侧蚀刻, 即可在二维方向上产生等效负介电常数和等效负磁导率.通过理论分析, 提出场-路结合的等效源分析法以计算等效介电常数、磁导率, 并据此对十字环型结构单元的左手特性激发机理进行了论证. 后采用Nicolson-Ross-Weir 等效参数法提取了十字环型单元阵列的相对介电常数和相对磁导率, 并通过棱镜实验对材料的负折射特性进行了验证.实验表明, 该左手材料在6.8-6.9 GHz频段具有二维入射左手特性. 此种左手材料制作工艺相对简单, 为左手材料在微波器件领域的应用提供了一种较为实用的设计方案.     

含负折射率材料的一维光子晶体的光学传输特性

采用光学传输矩阵方法,模拟研究了由正折射率材料和负折射率材料交替组成的一维光子晶体的光学传输特性.计算了这种含负折射率材料的一维光子晶体的透射谱和色散关系.结果表明,在正入射时,含负折射率材料的光子晶体的带隙要比传统的光子晶体要大得多,并具有狭窄的透射带,从光学薄膜理论的色散关系出发解释了形成上述现象的原因.讨论了在不同的偏振模式下,光以中心波长入射时,反射率随着入射角度的变化关系.发现含负折射率材料的一维光子晶体具有更好的角度特性,可以用来实现对中心波长的全方位反射.     

Possible negative refraction in two dimensional ferromagnetic wire lattice

In this paper, we present theoretical and experimental results for the indication of negative refraction in ferromagnetic metallic wire lattice. We have studied microwave transmission through a two dimensional wire lattice made of ferromagnetic metallic wires under the applied static magnetic field. We have found that, the microwave transmission were significantly changed at ferromagnetic resonance frequency region. Thus the magnetic permeability can be tuned by external dc magnetic field. Since the dielectric permittivity of metallic wire lattice is negative and can take a value close to unity then the crystal exhibits negative index of refraction at microwave region under the external magnetic field.     

Effect of spiral left-handed material with near-zero index on rectangular microstrip antenna

In this paper, spirals are arranged periodically on the surface of the substrate, making a left-handed material (LHM) with a near-zero index of refraction. A radiation patch is etched on the surface of this substrate, making an antenna. The finite difference time domain method is used to study the effect of this LHM with a near-zero index of refraction on the microstrip. At f=13.78 GHz, the equivalent permittivity and permeability of the proposed spiral materials are both negative; at f=28.02 GHz, the equivalent permittivity and permeability are both negative and the refraction index is near zero. Compared with conventional microstrip antenna, the radiation gain of the antenna is much higher and the return loss is much lower due to the near-zero-index effect.     

Negative refraction in ferromagnet-superconductor superlattices

Negative refraction, which reverses many fundamental aspects of classical optics, can be obtained in systems with negative magnetic permeability and negative dielectric permittivity. This Letter documents an experimental realization of negative refraction at millimeter waves, finite magnetic fields, and cryogenic temperatures utilizing a multilayer stack of ferromagnetic and superconducting thin films. In the present case the superconducting YBa2Cu3O7 layers provide negative permittivity while negative permeability is achieved via ferromagnetic (La:Sr)MnO3 layers for frequencies and magnetic fields close to the ferromagnetic resonance. In these superlattices the refractive index can be switched between positive and negative regions using external magnetic field as tuning parameter.     

Optical bistability in a defect slab with a negative refractive quantum dot nanostructure

We demonstrate optical bistability (OB) in a defect slab doped V-type four-level InGaN/GaN quantum dot nanostructure in the negative refraction frequency band. It has been shown that the OB behavior of such a quantum dot nanostructure system can be controlled by the amplitude of the driving fields and a new parameter for controlling the OB behavior as thickness of the slab medium in the negative refraction band. Meanwhile, we show that the negative refraction frequency band can be controlled by tuning electric permittivity and magnetic permeability by the amplitude of the driving fields and electron concentration in the defect slab doped. Under the numerical simulations, due to the effect of quantum coherence and interference, it is possible to switch bistability by adjusting the optimal conditions in the negative refraction frequency band, which is more practical in all-optical switching or coding elements, and technology based nanoscale devices.     

Negative and positive Goos–Hänchen shifts of a light beam transmitted from an indefinite medium slab

We study the lateral shift of a light beam transmitted from an indefinite medium slab. The analytic expressions for the transmission coefficient and the lateral shift are obtained by using the stationary-phase method, and different conditions for the occurrence of a negative lateral shift are deduced. It is shown that the thickness of the indefinite medium strongly affects the properties of the lateral shift. For a larger thickness, the sign of the lateral shift depends only on the signs of the permittivity and permeability, while, for a smaller thickness, the sign of the lateral shift is determined by the combined effect of the incident angle of the light, the signs of the permittivity and permeability, and the thickness of the indefinite medium slab. In addition, the lateral shift at the transmitted resonance points is found to be enhanced greatly, and the sign of the lateral shift around the transmitted resonance points is strongly dependent on the permittivity and permeability of the indefinite medium. Some examples are given to validate the obtained theoretical results. PACS 41.20.Jb; 42.25.Gy; 42.25.Bs; 78.20.Ci; 78.68.+m     

Spectral response and far-field pattern of a dipole nano-antenna on metamaterial substrates having near-zero and negative indices of refraction

In this work the resonance, frequency response, and far-field patterns of an optical nano-antenna placed on an interface between air and a metamaterial substrate is obtained through finite element calculations. The metamaterial is characterized by an effective, macroscopic index of refraction which can take negative and near-zero values, or by published values of the effective permittivity and permeability for metamaterials. The results show that the resonant wavelength and response can be fitted to analytical functions that are even functions of the index of refraction, this is consistent with the knowledge that negative indices of refraction allows for wave propagation in the same magnitude but opposite direction observed with positive indices of refraction. The simulations also show that substrates with near-zero index of refraction will enhance the antenna response by 62% compared to substrates with n > 1. Lossy metamaterials are also considered in the simulations. The far-field pattern of the antenna, obtained through a near-field to far-field transformation, behaves the same independently of the sign of the index of refraction, also the far-field pattern for the emission towards near-zero substrates is nearly constant and independent of the angle for the evaluated angular range.     

1.7—2.7GHz宽频带小单元异向介质设计及其介质参数提取

提出一种单元电尺寸小、工作频带宽、损耗小、结构简单的异向介质设计方案，在1.7—2.7 GHz上所设计的异向介质结构单元电尺寸小于0.035，相对带宽达到45.5%，在整个工作频带上单个结构单元传输损耗小于0.75 dB.对由上述异向介质单元构成的半无限大异向介质平板的电磁波反射、透射特性进行了数值仿真分析，并提取出了电磁波在该异向介质平板中传播时的波数、相速、折射率以及该异向介质平板的有效介电常数和有效磁导率等一系列电磁特性参数，仿真与计算结果表明复波数的实部、相速以及折射率的实部在1.7—2.7 GHz的范围上为负值，并且在相同频带上，有效介电常数和有效磁导率的实部同时为负值，从而有效地验证了“后向行波效应”、“负折射效应”、“双负效应”等异向介质特有的电磁特性，对上述异向介质的存在性给予有力证明. 关键词： 异向介质 宽频带 小单元 介质参数     

Negative-refractive bicrystal with broken symmetry produces asymmetric electromagnetic fields in guided-wave heterostructures

Heterostructure arrangements of uniaxial bicrystals have been discovered to produce electromagnetic fields with asymmetric distributions in guide wave structures. The property behind this remarkable phenomenon is the broken crystalline symmetry which allows the new physics to be seen in unsymmetric distributions. Here the theory behind this phenomenon is presented, numerical calculations are performed using an ab initio anisotropic Green's function approach, and the results provided at 10 GHz for a realistic crystal system with nominal permittivity of 5. Asymmetric distributions seen here are one facet of the broken symmetry property which generates negative refraction for impinging waves on a bicrystal.