Experimental verification and simulation of negative index of refraction using Snell's law

We report the results of a Snell's law experiment on a negative index of refraction material in free space from 12.6 to 13.2 GHz. Numerical simulations using Maxwell's equations solvers show good agreement with the experimental results, confirming the existence of negative index of refraction materials. The index of refraction is a function of frequency. At 12.6 GHz we measure and compute the real part of the index of refraction to be -1.05. The measurements and simulations of the electromagnetic field profiles were performed at distances of 14lambda and 28lambda from the sample; the fields were also computed at 100lambda.     

Experimental study of quasi-one-dimensional comb-like photonic crystals containing left-handed material

Quasi-one-dimensional comb-like photonic crystals with backbone waveguide made of left-handed material are physically fabricated by using transmission lines. The transmission properties are experimentally investigated and it is found that the structures possess a special band gap. The gap does not originate from the conventional Bragg scattering mechanism in that it is invariant with the change of scale length. Moreover, the experimental results indicate that the gap-edges are determined by zero-average permittivity of the branch and backbone and zero permeability of backbone, respectively. Because of the characteristics, it will be convenient to realize a special gap using in microwave and optical engineering.     

Snell's law of refraction observed in thermal frontal polymerization

We demonstrate that Snell's law of refraction can be applied to thermal fronts propagating through a boundary between regions that support distinct frontal velocities. We use the free-radical frontal polymerization of a triacrylate with clay filler that allows for two domains containing two different concentrations of a peroxide initiator to be molded together. Because the polymerization reaction rates depend on the initiator concentration, the propagation speed is different in each domain. We study fronts propagating in two parallel strips in which the incident angle is 90 degrees. Our data fit Snell's law v(r)/v(i)=sin theta(r)/sin theta(i), where v(r) is the refracted velocity, v(i) is the incident velocity, theta(r) is the angle of refraction, and theta(i) is the incident angle. Further, we study circular fronts propagating radially from an initiation point in a high-velocity region into a low-velocity region (and vice versa). We demonstrate the close resemblance between the numerically simulated and experimentally observed thermal reaction fronts. By measuring the normal velocity and the angle of refraction of both simulated and experimental fronts, we establish that Snell's law holds for thermal frontal polymerization in our experimental system. Finally we discuss the regimes in which Snell's law may not be valid.     

Magneto-optical effect of left-handed material

In this paper, we suggest a possibility of providing left-handed material with parallel ferromagnetic nanowires electrodeposited into an insulating polycarbonate membrane. We find that such a composite shows left-handed properties when the damping factor α satisfies α<α_c, where α_c is the critical damping factor which is affected by the filling factor of ferromagnetic nanowires. We also investigate the magneto-optical properties of such a composite and find that at the frequency region where the composite exhibits left-handed property, both the Faraday rotation angle and ellipticity of the film show obvious change apart from a jump in transmission coefficient at the frequency region near the ferromagnetic resonance frequency. Compared with the pure ferromagnetic film, a larger Faraday rotation angle is obtained in our model, which may be useful for the application of magneto-optical devices.     

Sub-wavelength imaging with a left-handed material flat lens

We study numerically, by means of the pseudospectral time-domain method, the unique features of imaging by a flat lens made of a left-handed metamaterial that possesses the property of negative refraction. We confirm the earlier finding that a left-handed flat lens can provide near-perfect imaging of a point source and a pair of point sources with clear evidence of sub-wavelength resolution. We illustrate the limitation of the resolution in the time-integrated image due to the presence of surface waves.     

Simple one-dimensional model of heat conduction which obeys Fourier's law.

We present the computer simulation results of a chain of hard-point particles with alternating masses interacting on its extremes with two thermal baths at different temperatures. We found that the system obeys Fourier's law at the thermodynamic limit. This result is against the actual belief that one-dimensional systems with momentum conservative dynamics and nonzero pressure have infinite thermal conductivity. It seems that thermal resistivity occurs in our system due to a cooperative behavior in which light particles tend to absorb much more energy than the heavier ones.     

Investigation of a patch antenna based on I-shaped left-handed material

The paper investigated a patch antenna based on I-shaped left-handed materials by using the method of finite difference time domain (FDTD). The results show that there exists a wave resonance state at 6.7 GHz, where the real part of the permittivity and permeability are all negative; the effect has largely enhanced the electromagnetic wave's resonance intensity, and has improved the localized extent of electromagnetic energy obviously in such medium, resulting in a higher antenna gain, a lower return loss, and a better improvement of the antenna's characteristics. Due to such advantages, the applications of patch antennas can be extended to such fields as mobile communication, satellite communication, aviation, etc.     

Propagation of Airy beams from right-handed material to left-handed material

Based on the ABCD matrix formalism,the propagation property of an Airy beam from right-handed material(RHM) to left-handed material(LHM) is investigated.The result shows that when the Airy beam propagates in the LHM,the intensity self-bending due to its propagation in the RHM can be compensated.In particular,if the propagation distance in the RHM is equal to that in the LHM and the refractive index of the LHM is n L =-1,the transverse intensity distribution of the Airy beam can return to its original state.     

双曲余弦高斯光束在左手平板材料中的传输特性

为了研究双曲余弦高斯光束在左手平板材料中的传输特性,运用广义惠更斯-菲涅耳衍射积分公式,推导出双曲余弦高斯光束在左手平板材料中的一般传输解析表达式。利用此表达式数字模拟了左手平板材料工作频率的变化对光束传输特性的影响。结果表明:双曲余弦高斯光束的中心光强、横向光强和光斑尺寸都可以用左手平板材料的工作频率来调控。随传输距离的增加,中心光强逐渐加强;在同一传输面上工作频率越大,中心光强越强。横向光强随工作频率的增大而增加,并且出现空心分布,光斑尺寸在加速扩展。     

The anomalous radiation force of light on a left-handed material

This paper derives the force of the electromagnetic radiation on left-handed materials (LHMs) by a direct applica-tion of the Lorentz law of classical electrodynamics.The expressions of radiation force are given for TE-polarised and TM-polarised fields.The numerical results demonstrate that electromagnetic waves exert an inverse lateral radiation force on each edge of the beams,that is,the lateral pressure is expansive for TE-polarised beams and compressive for TM-polarised beams.The investigation of the radiation force will provide insights into the fundamental properties of LHMs and will provide to better understanding of the interaction of light with LHMs.     

Giving birth to the refined unambiguous statement of Snell's law in ray optics

This paper reports on the ambiguity present in the long-running Snell's law of refraction of light, which is based on the traditional ambiguous definitions of the angles of incidence and refraction in ray optics. To get rid of the said ambiguity, the refined unambiguous definitions of angles of incidence and refraction reported earlier by the author have been employed to give birth to the refined unambiguous statement of Snell's law of refraction. The most interesting physical insights that resulted from the refined unambiguous statement of Snell's law are: (i) in case of refraction of light of a particular colour while passing from one optical medium to another, the ratio of the sine of the angle of incidence and the sine of the angle of refraction is approximately equal to the refractive index of the second optical medium with respect to the first optical medium and (ii) the refractive index of an optical medium ‘b’ with respect to another optical medium ‘a’ is approximately equal to the reciprocal of the refractive index of the optical medium ‘a’ with respect to the optical medium ‘b’, and vice versa. These results are entirely novel and different from those existing in the traditional literature of ray optics.     

THz频段单面左手材料的设计及仿真研究

本文运用等效参数提取方法验证了双线螺旋结构在不同频率处不仅能够实现负的磁导率, 而且可以实现负的介电常数. 在电磁波平行和垂直入射到双线螺旋结构表面两种情况下, 发现其负介电常数的形成机理相同. 以往的单面左手材料的研究仅仅局限于微波波段, 通过改进双线螺旋结构, 在THz频段设计出一种新型单面左手材料, 同时利用LC等效电路解释了其设计原理. 一般的左手材料是由刻蚀在基板两侧的电谐振器和磁谐振器组合而成的复合结构, 与这些复合结构相比, 这种新型单面左手材料具有低损耗, 结构简单, 易于加工等优点.     

Finite-size effects of a left-handed material slab on the image quality

The characteristics of an imaging system formed by a left-handed material (LHM) slab of finite length are studied, and the influence of the finite length of the slab on the image quality is analyzed. Unusual phenomena such as surface bright spots and negative energy stream at the image side are observed and explained as the cavity effects of surface plasmons excited by the evanescent components of the incident field. For a thin LHM slab, the cavity effects are found rather sensitive to the length of the slab; the bright spots on the bottom surface of the slab may stretch to the image plane and degrade the image quality.     

双通带异向平板波导的特性

提出了一种基于平板波导的新型异向谐振结构——交叉椅型谐振结构,通过理论分析和数值计算,说明和验证了单个交叉椅型谐振结构加载的平板波导具有双通带特性和异向特性;设计了一种由多个交叉椅型谐振结构周期加载的异向平板波导结构,并通过仿真实验验证了其负折射特性。交叉椅型谐振结构的全金属半封闭式结构和其特殊的电磁谐振方式,使得此类2维异向平板波导与传统的由金属开口谐振环与金属线正交阵列而成的2维异向介质相比,具有双通带、无介质损耗、功率容量大等特异性质;单个交叉椅型谐振结构加载的平板波导作为一种新型的滤波器结构,具有良好的双通带特性,尺寸较小。     

左手介质中电磁波的传播速度

在同向介质中,电磁波的群速度一般是能量传播的方向,并且电磁波的相速度和群速度在大部分情况下都满足瑞利关系.为了研究左手介质的电磁特性,本文从理论上导出了左手介质中电磁波的相速度、群速度及其关系,得出左手介质中电磁波的群速度为负,并介绍了左手介质的一些应用前景.     

Evanescent waves of an annular left-handed material lens

The imaging system formed by an annular left-handed material （LHM） lens as well as the evanescent waves in the lens are simulated numerically with a finite-difference time-domain （FDTD） method. For b - a 〉 λ （a and b are respectively the inner and outer radii of the annular lens, and λ is the wavelength）, when a point source is placed at an internal grid point, we demonstrate that the evanescent waves are produced around the internal interface, and cannot propagate outwards. As for b - a 〈λ ）,, the evanescent waves appear around both the internal and the external interfaces, which remarkably implies the coupling between the two interfaces. Hence it can be inferred that the evanescent waves around the external interface participating in the super-resolution imaging result from the coupling of the evanescent waves around the interface. Moreover, the partly uncomprehended properties of the evanescent waves in the LHM slab are also disclosed. It is conducive to understanding the evanescent waves in the LHMs further.     

双通带异向平板波导的特性

提出了一种基于平板波导的新型异向谐振结构——交叉椅型谐振结构,通过理论分析和数值计算,说明和验证了单个交叉椅型谐振结构加载的平板波导具有双通带特性和异向特性;设计了一种由多个交叉椅型谐振结构周期加载的异向平板波导结构,并通过仿真实验验证了其负折射特性。交叉椅型谐振结构的全金属半封闭式结构和其特殊的电磁谐振方式,使得此类2维异向平板波导与传统的由金属开口谐振环与金属线正交阵列而成的2维异向介质相比,具有双通带、无介质损耗、功率容量大等特异性质;单个交叉椅型谐振结构加载的平板波导作为一种新型的滤波器结构,具有良好的双通带特性,尺寸较小。     

Propagation of rotating elliptical Gaussian beams from right-handed material to left-handed material

By applying the ABCD matrix method, we report the propagating properties of the rotating elliptical Gaussian beams(REGBs) from the right-handed material(RHM) to the left-handed material(LHM). Based on the propagation equation, we obtain the intensity distributions of the REGBs during the propagation. It is found that the rotating direction of the REGBs is opposite in the RHM and the LHM, and the rotation angles tend to be π /2 as the propagation distance is long enough.Then we analyze the relationship between the refractive index and the rotating velocity. Furthermore, the energy flow and the angular momentum(AM) of the REGBs which can rotate are also obtained.     

Analysis of resonator modes in two-dimensional laser cavities containing a left-handed material

Resonator modes in two-dimensional laser cavities with curved end mirrors filled with a left-handed material were investigated numerically using the extended Fox-Li mode calculation method. The results reveal that the phase profile on the curved end mirrors of a left-handed cavity is inverted relative to that of a cavity filled with a right-handed material. Furthermore, we show that the phase on the end mirrors takes discrete values of zero and ±π under stable resonator conditions, while it varies continuously under unstable resonator conditions. The differences between stable and unstable resonators significantly alter the far-field patterns of the lowest-loss modes.     

Focusing and phase compensation of paraxial beams by a left-handed material slab

On the basis of angular spectrum representation, a formalism describing paraxial beams propagating through an isotropic left-handed material (LHM) slab is presented. The treatment allows us to introduce the ideas of beam focusing and phase compensation by LHM slab. Because of the negative refractive index of LHM slab, the inverse Gouy phase shift and the negative Rayleigh length of paraxial Gaussian beam are proposed. It is shown that the phase difference caused by the Gouy phase shift in right-handed material (RHM) can be compensated by that caused by the inverse Gouy phase shift in LHM. If certain matching conditions are satisfied, the intensity and phase distributions at object plane can be completely reconstructed at the image plane.