波状结构二维光子晶体负折射现象的研究

结合波状结构二维(2D)光子晶体(PC)与入射介质两者的等频面结构分析了PC内部的负折射现象，采用时域有限差分(FDTD)方法模拟了高斯光束在波状结构2DPC内的负折射，分别得到了折射角/入射角以及折射角/入射波长之间的关系曲线，当入射角为45°，入射波段在1485—1530nm区域时，波状结构2DPC的负折射角与入射波长近似呈线性变化关系，并带有明显的PC超棱镜效应，采用端面投影方法对波状结构2DPC的入射端面和出射端面进行处理，改善了负折射时的透过率. 关键词： 光子晶体 负折射 等频面     

Negative refraction in one-dimensional plasma photonic crystals

We have theoretically explored the negative refraction (NR) in one-dimensional plasma photonic crystals (PCs) consisting of plasma and dielectric materials. By using the transfer matrix method and Bloch theorem, we have studied the group velocity and we have obtained the NR in plasma PCs with the help of the group velocity. The results show that plasma PCs can also exhibit the NR although they have a periodically modulated positive permittivity ? and permeability μ. It is also shown that the NR in plasma PCs exhibits difference behaviour in different frequency regions, ω < ω_p and ω > ω_p, respectively. The parameter dependence of the effects is also examined and discussed.     

Negative refraction in photonic crystals

We demonstrate that light propagation in strongly modulated 2D/3D photonic crystals (PhCs) becomes refraction-like in the vicinity of the photonic bandgap, which is contrary to the fact that light propagation in weakly modulated PhCs is very different from refraction and thus the definition of refraction index becomes meaningless. Such a crystal behaves like a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. The propagation states having a negative effective index exhibit unusual properties, such as mirror-like imaging effect, image-transfer effect. These properties are confirmed by finite-difference time-domain simulations.     

Existing conditions of full bandgaps and absolute negative refraction in metallic-dielectric photonic crystal

This paper has theoretically studied the characteristic frequencies of band structures in two-dimensional metallic-dielectric photonic crystals. It is demonstrated that a large filling fraction benefits the existence of absolute photonic band gap, while a smaller filling fraction benefits an absolute negative refraction band. In addition, it also finds that the relation between the cut-off frequency of E-polarized wave and the filling fraction exceeding 10{\%} is content with a linear increasing function, whose coefficients are exponential to the normalized lattice constant. These investigations have significant implications for tuning the operational frequencies to desired applications and manufacturing photonic crystals.     

利用含负折射率材料的光子晶体实现角度滤波器

利用光子晶体的共振隧穿效应，并结合由负折射材料引起的零平均折射率带隙，设计出一种新型的角度滤波器，使得对于某一频率范围内的入射电磁波仅在特定入射角度的波能够全透，而其他角度的波不能透过.这将在微波器件乃至光学器件上有广泛应用. 关键词： 光子晶体 负折射率材料 共振隧穿     

二维空气孔型光子晶体负折射平板透镜的减反层

提出并优化了由单排渐变介质波导构成的二维空气孔型光子晶体负折射平板透镜表面的减反层，改善了成像质量.二维时域有限差分模拟计算结果表明，采用减反层后，在入射角小于23°的范围内，在使得有效折射率n_eff=-1的工作频率处，光子晶体表面对从空气一侧入射的平面波的反射率可降低到1％以下. 关键词： 光子晶体 负折射 平板透镜 减反层     

正负折射率材料组成的半无限一维光子晶体的反射率

计算了由正负折射率材料交替生长形成的半无限一维光子晶体的反射率,发现在带隙中,反射率等于1,在通带内,半无限结构的反射率是有限层结构迅速振荡的反射率平均的结果. 当该结构中正负折射率材料的光学厚度相互抵消时,会出现零平均折射率能隙.解析地证明了该结构零平均折射率附近的能隙几乎不随入射角度和偏振情况变化,而且跟晶格常数的标度无关. 关键词： 半无限光子晶体 反射率 负折射率     

Negative refraction and focusing of electromagnetic wave through two-dimensional photonic crystals

The negative refraction of electromagnetic waves in photonic crystals was recently demonstrated experimentally, and the physical properties were analyzed. Microsuperlenses based on two-dimensional photonic crystals were designed and the subwavelength images were observed. In this review, after providing a brief history of the research related to the above phenomena, we will summarize our research works in this field including the method of creating a negative refraction region, generating an absolute negative refraction, the focusing of unpolarized electromagnetic waves, and the effect of interface and disorder on the image by the two-dimensional photonic crystal flat lens. The discussion on the negative refraction and the focusing by high symmetric quasicrystals is also presented.     

二维蜂窝格子光子晶体的远场成像特性及界面对成像质量的影响

利用有限时域差分法研究了一种二维蜂窝格子光子晶体的远场亚波长成像特性，发现和折射率为-1时的负折射成像规律符合得很好.但是由于晶格结构本身的特性，入射光以大角度入射时，这种结构的耦合效率很低，影响了像的强度和质量.通过适当改变界面上介质柱的半径的方法可以提高耦合效率，进而有效提高成像的质量和强度.     

基于硅柱-磁性液体体系的光子晶体的可调谐负折射特性研究

本文研究了硅柱在MnFe₂O₄磁性液体背景中排列成六边形结构的二维光子晶体的可调谐负折射特性. 利用平面波展开法和时域有限差分法理论研究了硅柱-磁性液体体系二维光子晶体的带隙结构、等频曲线和负折射现象随外磁场强度的变化关系. 模拟结果表明, 硅柱-磁性液体体系二维光子晶体工作在TE模式时, 其负折射特性可由外磁场调节. 在固定背景溶液的磁性颗粒体积分数和入射光频率时, 所研究的折射光束的偏转角和光子晶体的负折射率绝对值随外磁场的增大而增大, 而在固定背景溶液的磁性颗粒体积分数和外磁场强度时, 负折射角和负折射率的绝对值随入射光归一化频率增大而减小. 固定外场强度和入射光频率时, 所研究结构的负折射特性随背景溶液的磁性颗粒体积分数增大而变弱.     

正负折射率材料组成的一维光子晶体的能带及电场

计算了由正负折射率材料交替排列组成的一维光子晶体的能带及电场，发现其能带不同于由普通正折射率材料组成的光子晶体的能带.当选择合适的参数时，由正负折射率材料组成的光子晶体的TE模或TM模有完全光子带隙出现，这在普通光子晶体中不出现.导带中的电场波函数与普通光子晶体相比具有很强的局域性.对于负折射率材料层为色散介质的情况，计算了在不同的具有正负折射率区域能带.     

基于空气孔的光子晶体亚波长成像的特性研究

负折射率材料因为其奇异的特性成为广泛研究的对象,尤其是光子晶体平板的完美成像.本文采用空气孔在硅介质中周期性排列构成六角结构的光子晶体结构,用平面波展开法及FDTD方法,研究了该光子晶体的亚波长成像能力还研究了入射波长以及温度漂移对该光子晶体平面亚波长成像的影响.     

Negative refraction and imaging properties of circular photonic crystals

The electromagnetic wave propagation in a two-dimensional (2D) circular photonic crystal (CPC) is investigated. The CPC structure is composed of air holes in the dielectric background material. The finite element method is used to study the optical and propagating properties of the CPC slab. Numerical simulations show that negative refraction and near-field imaging can appear in a 2D CPC slab. We also find that the high-symmetry CPC slab possesses an optics axis along the vertical direction intersecting the symmetric center. As a result, the CPC slab can exhibit an excellent imaging performance when a source is placed on the optical axis.     

蜂巢光子晶格中光波的无衍射和反常折射

空间频率模式的光子带隙反映了光波在周期性结构中的线性传输特性.以这种线性传输特性为基础,研究了蜂巢光子晶格中光波的无衍射和反常折射.通过详细分析带隙结构第一通带上的衍射与折射特性,得出了光波发生反常衍射和折射的入射条件.匹配不同的入射条件,数值模拟了光波的无衍射传输和反常折射现象.结果表明:将入射光束的波矢设置在蜂巢晶格布里渊区中正常、反常衍射区的交界处,可使高斯光束沿x轴、y轴方向的衍射得到有效抑制;以多光束干涉场作为入射光场,可对蜂巢晶格进行模式匹配,激发第二布里渊区的传输模式;进一步将模式匹配后入射光场的波矢设置在反常折射区,可实现光波的反常折射.     

Omnidirectional reflection in one-dimensional ternary photonic crystals and photonic heterostructures

Designing dielectric systems to create omnidirectional band gaps (OBGs) is an attractive topic in the field of photonic band gap (PBG) structures. In this Letter, we propose a new approach to create OBGs by ternary photonic heterostructures (TPHs) composed of three kinds of materials with different refractive indices and obtain the formulae of the structures of TPHs, i.e., those of the thicknesses of materials and the number of sub-ternary photonic crystals. It may provide a powerful technique for designing the structures being able to produce OBGs by use of usual materials, lowcost materials, and materials with low refractive indices, etc.     

单轴晶体中负折射现象的演示

用惠更斯作图法定性地说明了单轴晶体中负折射现象产生的基本原理,演示了YVO4晶体中发生的负折射现象.该实验有助于学生全面认识折射现象.     

含负折射率材料并具有零平均折射率的半无限一维光子晶体的表面态

用传输矩阵方法和Bloch定理,从理论上分析以色散介质为背景,由正负折射率材料组成的半无限一维光子晶体的表面态,发现以色散介质为背景,在满足平均折射率等于零的情况下,第一层厚度变化时,表面态将会在较大频率范围内显著变化。讨论了同一入射角度下不同频率的表面态的电场分布情况,结果表明：远离带边的表面态局域长度较小。     

色散负折射特异介质的1维光子晶体缺陷态

在1维光子晶体中引入色散负折射特异介质,分析了其介电常数和磁导率在微波区（1～10 GHz）与频率的关系。分别对以色散负折射介质为缺陷的正折射率介质光子晶体及以正折射率介质为缺陷的正负折射率介质光子晶体进行了数值仿真,得出了均匀平面电磁波在正入射和斜入射时的透射谱。结果表明:在介电常数和磁导率均为负值的不同禁带中,分别出现了单、双缺陷模。利用透射谱的这一特点,可实现单、双通道滤波。     

Band rules for the frequency spectra of three kinds of aperiodic photonic crystals with negative refractive index materials

By means of the theory of electromagnetic wave propagation and transfer matrix method, this paper investigates the band rules for the frequency spectra of three kinds of one-dimensional (1D) aperiodic photonic crystals (PCs), generalized Fibonacci GF(p,1), GF(1,2), and Thue--Morse (TM) PCs, with negative refractive index (NRI) materials. It is found that all of these PCs can open a broad zero-? gap, TM PC possesses the largest zero-? gap, and with the increase of p, the width of the zero-? gap for GF(p,1) PC becomes smaller. This characteristic is caused by the symmetry of the system and the open position of the zero-? gap. It is found that for GF(p,1) PCs, the possible limit zero-? gaps open at lower frequencies with the increase of p, but for GF(1,2) and TM PCs, their limit zero-? gaps open at the same frequency. Additionally, for the three bottom-bands, we find the interesting perfect self-similarities of the evolution structures with the increase of generation, and obtain the corresponding subband-number formulae. Based on 11 types of evolving manners Q_i(i=1,2,....,11) one can plot out the detailed evolution structures of the three kinds of aperiodic PCs for any generation.     

色散负折射特异介质的1维光子晶体缺陷态

在1维光子晶体中引入色散负折射特异介质,分析了其介电常数和磁导率在微波区（1～10 GHz）与频率的关系。分别对以色散负折射介质为缺陷的正折射率介质光子晶体及以正折射率介质为缺陷的正负折射率介质光子晶体进行了数值仿真,得出了均匀平面电磁波在正入射和斜入射时的透射谱。结果表明：在介电常数和磁导率均为负值的不同禁带中,分别出现了单、双缺陷模。利用透射谱的这一特点,可实现单、双通道滤波。