二维色散和各向异性磁化等离子体光子晶体色散特性研究

采用平面波展开法和时域有限差分法研究了二维色散和各向异性磁化等离子体光子晶体的色散特性.当波矢在周期平面时,由于外加磁场的作用使TE模的色散曲线出现两个不同区域的平带,改变磁场的大小不但可以控制平带的位置,而且可以控制光子带隙的位置和大小.增大背景材料的介电常数,可以形成全方向光子带隙,随着背景材料介电常数的增加,带隙的中心位置降低但带隙宽度增加.当波矢偏离周期平面时,色散曲线不再分为TE和TM模,随着非周期平面波矢的增加,带隙位置上移,带隙宽度先增加随后基本保持不变.     

Optical properties of chiral photonic crystals in an external static magnetic field

Oblique propagation of light through a layer of a gyrotropic crystal in an ultrasonic field in the presence of an external static magnetic field is analyzed. The problem is solved using the Ambartsumyan method of addition of layers. The results of analysis of dependences of amplitude and polarization characteristics on the wavelength of light are presented for various values of parameters of the problem. The possibility of applying such systems is discussed.     

横磁模式下二维非磁化等离子体光子晶体的线缺陷特性研究

采用等离子体的分段线性电流密度卷积时域有限差分算法研究了横磁波入射时具有单一线缺陷的二维非磁化等离子体光子晶体的缺陷模特性. 从频域角度分析得到微分高斯脉冲的透射系数,并讨论该光子晶体的晶格常数、介质圆柱半径、周期常数、缺陷层参数和等离子体参数对缺陷模特性的影响. 结果表明,改变周期常数、缺陷层位置和等离子体碰撞频率不会改变缺陷模的频率,改变缺陷层介质圆柱的相对介电常数、半径和缺陷层到介质层的中心距离可以在不改变禁带宽度的前提下实现对缺陷模的调节,改变晶格常数、介质圆柱半径和等离子体频率能同时实现对禁带宽度和缺陷模的调节. 关键词： 等离子体 光子晶体 缺陷模 时域有限差分算法     

Band gap characteristics of plasma with periodically varying external magnetic field

The reflectance characteristics of a one-dimensional periodically magnetized plasma structure is studied by using the transfer matrix method. It is found that this system has the band gap characteristics of photonic crystals, so we also name it a plasma photonic crystal. The results show that the gap location and gap width can be controlled by the incident angle. If the external magnetic field is small, the gap location and gap width change significantly with incident angle, while they change only slightly when the external magnetic field is sufficiently large. The collision frequency has little effect on the gap location and gap width while it makes the amplitude of reflectance and transmission decrease. This new type of plasma photonic crystal could have potential applications in designing tunable photonic crystal devices.     

Band-gap properties of two-dimensional low-index photonic crystals

We study the band-gap properties of two-dimensional photonic crystals created by a lattice of rods or holes conformed in a symmetric or asymmetric triangular structure. Using numerical plane-wave method, we calculate a minimum value of the refractive-index contrast for opening both partial and full two-dimensional spectral gaps for both TM- and TE-polarized waves. We also analyze the effect of ellipticity of rods and holes and their orientation on the threshold value and the relative size of the band gaps.     

Dispersion characteristics of two-dimensional unmagnetized dielectric plasma photonic crystal

This paper studies dispersion characteristics of the transverse magnetic (TM) mode for two-dimensional unmagnetized dielectric plasma photonic crystal by a modified plane wave method. First, the cutoff behaviour is made clear by using the Maxwell--Garnett effective medium theory, and the influences of dielectric filling factor and dielectric constant on effective plasma frequency are analysed. Moreover, the occurence of large gaps in dielectric plasma photonic crystal is demonstrated by comparing the skin depth with the lattice constant, and the influence of plasma frequency on the first three gaps is also studied. Finally, by using the particle-in-cell simulation method, a transmission curve in the \Gamma -X direction is obtained in dielectric plasma photonic crystal, which is in accordance with the dispersion curves calculated by the modified plane wave method, and the large gap between the transmission points of 27~GHz and 47~GHz is explained by comparing the electric field patterns in particle-in-cell simulation.     

Wave dispersion relation of two-dimensional plasma crystals in a magnetic field

The wave dispersion relation in a two-dimensional strongly coupled plasma crystal is studied by theoretical analysis and molecular dynamics simulation taking into account a constant magnetic field parallel to the crystal normal. The expression for the wave dispersion relation clearly shows that high-frequency and low-frequency branches exist as a result of the coupling of longitudinal and transverse modes due to the Lorenz force acting on the dust particles. The high-frequency and the low-frequency branches are found to belong to right-hand and left-hand polarized waves, respectively.     

Magnetic surface plasmon-induced tunable photonic bandgaps in two-dimensional magnetic photonic crystals

We experimentally studied magnetically controllable photonic band gaps (PBGs) in two-dimensional magnetic photonic crystals consisting of ferrite rods. Besides the conventional PBG that relates to Bragg scattering, two other types of PBG, resulting from magnetic surface plasmon (MSP) resonance and spin-wave resonance, respectively, are observed. The PBG due to MSP resonance is particularly interesting because of its analogy to surface plasmon in metal; furthermore, it is shown to be completely tunable by an external static magnetic field from both an experimental and a theoretical point of view.     

Band gap properties of two-dimensional photonic crystals with rhombic lattice

A new structure of two-dimensional photonic crystals (PCs) with rhombic lattice is proposed in this paper. It provides more flexibility in the design of photonic crystal devices and makes the designer be able to choose a more suitable lattice angle to satisfy different demands. The first Brillouin zone (1st BZ) of this structure is discussed and the general wave vectors are derived. The plane wave expansion (PWE) method is used to analyze the band gap properties. The impact of different lattice angels on the band gaps is analyzed, and the band gap map is also given.     

Dispersion properties of two-dimensional phonon crystals with a hexagonal structure

Acoustic and optical properties of two-dimensional phonon crystals with a hexagonal symmetry are described. Differential-difference equations describing plane oscillations of a two-dimensional lattice of material structures are derived in a harmonic approximation, and dispersion dependences of acoustic and optical phonons are calculated. Branches of optical oscillations and intervals of forbidden frequencies are shown to appear when a lattice consists of two types of atoms.     

Localized defect modes in finite magnetic two-dimensional photonic crystals

We present a detailed study of localized defect modes in finite two-dimensional magnetic photonic crystal consisting of cylindrical ferrite material in air background by using the scattering matrix method. It is shown that due to having positive and negative value of the effective magnetic permeability in interested photonic band gap, the defect modes present different behavior. Our results show that the modes appeared in positive permeability region have features similar to the modes supported by the dielectric photonic crystal while those created in the negative permeability region are strongly localized at the interface of defect ferrite rod with air background. Moreover, results indicate that defect modes occurred in the negative region are sharper than those appeared in the positive one which means the quality factor of former case is extremely high.     

外磁场与温度对低温超导光子晶体低频禁带特性的影响

文中用传输矩阵法(TMM)分析了TM波垂直入时,超导光子晶体的低频禁带特性,并讨论了外磁场与温度对禁带的影响.分析结果表明:超导光子晶体存在频率从0开始的低频禁带;当没有外磁场作用时,由于超导中正常态电子的影响,低频禁带的截止频率与温度无关;有外磁场作用时,温度才对截止频率具有可调性.外加恒定磁场时,低频禁带的截止频率随温度升高而减小;而在正常态电子的作用下,温度对处在超导态超导光子晶体禁带截止频率的调节范围相对忽略正常态电子情况下减小.恒温下,通过调节外磁场来控制带隙时,正常态电子的贡献很小可忽略不计;外磁场强度增大禁带截止频率减小.当超导体完全处于正常态时,低频禁带消失.     

The properties of two-dimensional photonic crystals bandgap structure with rhombus lattice

The relative bandgap ω_R of photonic crystals structure with rhombus lattice for both TE and TM modes is studied by the plane wave expansion method. Based on the analysis, a bending waveguide of U type can be easily obtained. The steady-state distribution of the electric field with ω = 0.4765(a/λ) of TM mode is given by FDTD method and the transmission is obtained by FFT of the time domain field. All of the sufficient analysis shows the conceptual framework of the proposed rhombus lattice PCs and its great potential application in photonic integration circuit.     

二维正方格子磁性光子晶体的带隙结构

采用平面波展开的方法计算了正方格子二维磁性光子晶体(MPC)的光子带隙结构.散射子的形状分别为：长方形，正方形，六角形和圆形.通过调节磁导率，填充率和散射子的旋转角度，找到了MPC各种结构的最大的绝对带隙宽高比ω_R.研究发现：随着磁导率的增加，MPC绝对带隙中心频率ω_g单调减小，绝对带隙宽度Δω和其宽高比ω_R可能不同时达到最大值.而随着填充率或者散射子旋转角的增加，基本不改变ω_g的大小，各种结构的Δω和ω_R同时达到最大值. 关键词： 磁性光子晶体 光子带隙结构     

Properties of the band gap of two-dimensional plasma photonic crystals

Employing the finite-difference time-domain (FDTD) method, we study the filtering properties of twodimensional plasma photonic crystals. We show that the transmission spectra of the defects in the plasma photonic crystals vary with change in the defect location, its radius, the plasma frequency, and the frequency of electron–ion collisions in the plasma. We demonstrate that the two-dimensional defect structure from the viewpoint of its frequency characteristic (such as an adjustable filter characteristic) is similar to the one-dimensional structure. We find that by changing the parameters of the defect location, the plasma frequency, and the frequency of electron–ion collisions in the plasma, one can obtain different ranges of transmission peaks at different frequencies, which fully reflects the adjustable filter characteristics of the structure. Therefore, the two-dimensional structure is more important than the one-dimensional structure, and it can be used to produce actual microwave devices.     

On the theory of optical properties of anisotropic magnetic crystals in external magnetic field

The calculation of dielectric permeability tensor which are based on the theory of excitons in magnetoordered crystal are made. The dipole exciton energies of crystal are obtained and their dependence on external magnetic field H at arbitrary relation between exchange and single-ion anisotropy constants is established. Refractive index of tetragonal antiferromagnetic is determined and it is shown that it (index) is an odd function of H for a light polarized transverse to the fourth-order symmetry axis of crystal.     

Spontaneous emission in the near field of two-dimensional photonic crystals

We show theoretically that photonic crystal membranes cause large variations in the spontaneous emission rate of dipole emitters, not only inside but also in the near field above the membranes. Our three-dimensional finite-difference time-domain calculations reveal an inhibition of more than five times and an enhancement of more than ten times for the spontaneous emission rate of emitters with select dipole orientations and frequencies. Furthermore, we demonstrate theoretically the potential of a nanoscopic emitter attached to the end of a glass fiber tip as a local probe for mapping the large spatial variations of the photonic crystal local radiative density of states. This arrangement is promising for on-command modification of the coupling between an emitter and the photonic crystal in quantum optical experiments.     

Negative refraction and left-handed properties in two-dimensional photonic crystals

We report on the negative refraction and left-handed behavior of two-dimensional photonic crystals. For the triangular two-dimensional photonic crystals there are two saddle points and a key point in the first Brillouin zone for the second band, which play important role to determine the refraction phenomena. There is no determined relation between the left-handed behavior and the negative refraction. The refraction phenomena depend on the band structure and the configuration of the incident light. For the first configuration, the first Brillouin zone can be divided into three parts. In part I there are negative refraction and left-handed behaviors. In part II there are normal refraction and left-handed behaviors. In part III there are normal refraction and right-handed behaviors. For the second configuration, the first Brillouin zone can only be divided into two parts. For these complex refraction phenomena, it is meaningless to define the phase refractive index, and it is necessary to define the effective refraction index by a Snell-like formula, and the value of the effective index is determined by the configuration and the band structure.