通信波段硅基气孔光子晶体的带隙特性及其物理模型研究

用平面波展开法对硅背景下的通信波段不同晶格类型和气孔形状光子晶体的能带结构进行数值计算与分析,提出了相应的物理模型.结果表明:利用光子受限效应和晶格对称性效应可以有效地调控光子带隙.随光子晶体填充率的增加,其约束光子的能力增强,光子带隙在一定范围内展宽且其中心频率蓝移;带隙随晶格对称性增加而变宽.对基元形状和旋转角度的研究发现,光子带隙随基元旋转角度变化具有周期性和对称性,表现出各向异性,由此优化出对应的不同晶格的最佳谐振腔型结构.     

Lieb晶格等离子体光子晶体基元结构原位调控

利用独特设计的阵列-液体电极介质阻挡放电装置,率先获得了Lieb晶格等离子体光子晶体,并实现了其基元大小、形状和微观形貌的多自由度原位调控。采用光电倍增管对Lieb晶格等离子体光子晶体的时空动力学行为进行了时空分辨测量。基于有限元计算,对不同基元结构的Lieb晶格等离子体光子晶体的色散关系和能带变化规律进行了系统研究。结果表明：Lieb晶格等离子体光子晶体由两套不同四方子晶格相互嵌套形成,具有优异的时空稳定性和周期性;随着Lieb晶格基元构型的改变,光子带隙发生显著变化,形成了偶然简并的类狄拉克锥结构,以及不同频段的完全带隙和非完全带隙;基元的几何形状对光子带隙数目、位置和宽度均具有重要影响。     

二维复式声子晶体中基元配置对声学能带结构的影响

研究了二维复式声子晶体中基元配置对其声学能带结构的影响,发现当声子晶体的基元配置改变时,声子晶体的不可约布里渊区也会改变,而且部分能带的极值不再在高对称线上.特别地,在某些基元配置下,不可约布里渊区扩大为整个第一布里渊区.因此,对于对称性较高的复式晶格声子晶体,可用通常的方法得到能带结构,而对于对称性较低的复式晶格结构声子晶体,只有采用对整个第一布里渊区进行研究的方法,才能获得可信的能带结构及带隙.     

类蜂窝状结构完全带隙二维光子晶体

通过在二维三角晶格中引入两个完全一样的介质圆柱构成了类蜂窝状结构光子晶体,并对其光子能带进行了频域计算。借助数值方法分析了介质柱位置改变对光子能带的影响,计算结果表明,这种类蜂窝状结构二维光子晶体可以产生很宽的带隙,而且在一定填充率下,可以通过调整介质柱的位置使完全光子带隙达到最大化。     

基于六角结构二维光子晶体绝对带隙的优化设计研究

根据平面波展开法对二维光子晶体的能带结构进行计算，采用栅格结构连接电介质圆柱体对六角结构的二维光子晶体进行了优化. 通过计算栅格宽度和圆柱体半径对绝对带隙的影响，找到了一组可以获得大带隙二维光子晶体结构的最佳参数.优化后的光子晶体的大带隙对光子晶体制造工艺中介质圆柱体半径的偏离具有很好的稳定性，因此该结构的二维光子晶体具有很高的实用性. 关键词： 光子晶体 绝对带隙 六角结构     

基于光子晶体塔姆态的带隙分裂

将由两个一维介质层光子晶体组成的异质结拓展为超晶格结构,分析了该结构的能带和透射谱。该超晶格结构可以产生多个界面隧穿态,它们之间的耦合可产生新的通带。研究结果表明,该通带的宽度随光子晶体的周期数变化,而通带的中心位置保持不变。当光子晶体周期数取特定值时,这个通带将发生分裂,在带间产生零相位带隙或π相位带隙。     

旋转对二维正方晶格介质柱内空结构光子晶体禁带的影响

采用平面波展开的方法计算了三种旋转操作下二维正方晶格各向异性材料(Te)介质柱内空结构光子晶体TE,TM模式能带.讨论了三种旋转操作对TE,TM模式带隙及完全光子禁带的影响.发现TM模式高频带隙与结构的旋转对称性有着密切的关系.而TE模式的带隙不仅受到晶体旋转对称性的影响同时也受到介质在x-y平面分布情况的影响. 关键词： 二维光子晶体 内空结构 旋转操作 光子带隙     

结构参数对聚苯乙烯光子晶体能带结构的影响

本文讨论了平板式光子晶体能带结构的计算方法,并利用平面波展开法研究了聚苯乙烯材料制作的平板式光子晶体的能带结构与晶格类型、填充比两个主要结构参数之间的关系.计算给出了晶格类型及填充比发生变化时光子禁带的变化规律.研究发现,当填充比(r/a)介于0.1～0.5之间时,四边形晶格结构和六角形晶格结构奇模和偶模均存在光子带隙,蜂窝状晶格只有偶模存在光子带隙,而且只有当填充比r/a＞0.46时才出现光子带隙.本文所得结果对聚苯乙烯光子晶体的制作和进一步应用研究奠定了理论依据.     

一种衍生于三角晶格的二维光子晶体

通过在二维三角晶格中引入三个完全相同的介质圆柱构成了一种全新结构的光子晶体,并对其光子能带进行了频域计算.借助数值方法分析了填充率对光子能带的影响,结果表明,在一定填充率下,这种二维光子晶体对于E偏振和H偏振都存在很宽的带隙,而且还可以获得一个窄完全带隙.     

介质中间层的引入对光子晶体薄板特性的影响

利用导模展开方法计算得到了三角格子三组分光子晶体薄板的能带结构和固有损耗.在光子晶体薄板中引入的第三组分中间介质层对光子晶体薄板的能带结构和固有损耗有着显著的影响.光子带隙宽度与带隙边界的位置与中间介质层的厚度和其介电常数大小紧密相关,随着中间介质层的厚度或中间介质层的介电常数的增加,带隙边界移往低频,而各能带所对应的次导模所受固有损耗减小.     

Absolute photonic band gaps of two-dimensional square-lattice photonic crystals with Taiji-shaped dielectric rods

A novel structure of two-dimensional (2D) square-lattice photonic crystal (SLPC) composed of Taiji-shaped dielectric rods imbedded in air is constructed and the properties of absolute photonic band gap (PBG) are theoretically analyzed in both the number and width by Plane Wave Expansion Method (PWM). By comparing the absolute PBGs in 2D SLPCs consisting of four shapes of rods with different symmetries (circle, button, semicircle and Taiji) at the same filling ratio, we find that both the number and width of absolute PBG significantly increase with the breaking of scatterer's symmetry, and the Taiji-shaped rods with the poorest symmetry can attain both the most number and the largest width of absolute PBGs. Additionally, we also study the influence of dielectric constant ε and three geometric parameters of Taiji-shaped scatterer on the absolute PBG and discover that the SLPC with Taiji-shaped rods can generate at most nine absolute PBGs and the largest absolute PBG with the width 0.0485 (ωa/2πc).     

Study on the anisotropic photonic band gaps in three-dimensional tunable photonic crystals containing the epsilon-negative materials and uniaxial materials

In this paper, the properties of anisotropic photonic band gaps (PBGs) for three-dimensional (3D) photonic crystals (PCs) composed of the anisotropic positive-index materials (the uniaxial materials) and the epsilon-negative (ENG) materials with body-centered-cubic (bcc) lattices are theoretically studied by a modified plane wave expansion (PWE) method, which are the uniaxial materials spheres inserted in the epsilon-negative materials background. The anisotropic photonic band gaps (PBGs) and one flatbands region can be achieved in first irreducible Brillouin zone. The influences of the ordinary-refractive index, extraordinary-refractive index, filling factor, the electronic plasma frequency, the dielectric constant of ENG materials and the damping factor on the properties of anisotropic PBGs for such 3D PCs are studied in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in such 3D PCs with bcc lattices composed of the ENG materials and uniaxial materials, and the complete PBGs can be obtained compared to the conventional 3D PCs containing the isotropic materials. The calculated results also show that the anisotropic PBGs can be manipulated by the parameters as mentioned above except for the damping factor. Introducing the uniaxial materials into 3D PCs containing the ENG materials can obtain the larger complete PBGs as such 3D PCs with high symmetry, and also provides a way to design the tunable devices.     

传输可见光的空芯光子带隙光纤的研究

利用全矢量平面波展开法(FVPWM)对采用改进的两次堆积法制备的空芯光子带隙光纤进行了数值模拟.在特定传播常数β下,光纤在500—1000 nm的波段内出现多条宽窄不同的有效光子带隙.依据有效折射率的不同,部分带隙中的空气-导模将以不同的形式存在.经过实验测试,发现测得的带隙位置相对于模拟结果向短波段发生了较明显的移动,主要原因被认为是光纤结构的纵向不均匀性和包层节点处间隙孔的存在. 关键词： 空芯光子带隙光纤 全矢量平面波展开法 有效光子带隙 空气-导模     

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.     

在高频区存在巨带隙的长方晶格二维光子晶体

本文利用降低光子晶体的对称性来提高绝对禁带宽度, 提出两种长方结构长方介质柱二维光子晶体, 用快速平面波展开法研究其高频区的带结构.经参数优化发现, 长方晶格包含一套介质柱时, 最大绝对禁带宽度Δω为0.1265ωe（ωe=2πc/a, a为晶格常数, c为光速）, 绝对禁带中心频率ωmid为1.9256ωe, Δω/ωmid=6.6%; 当长方晶格包含两套介质柱时, 最大绝对禁带宽度为0.203ωe, 绝对禁带中心频率为1.8597ωe, Δω/ωmid=10.9%.     

A Novel Woodpile Three-Dimensional Terahertz Photonic Crystal

A novel woodpile lattice structure is proposed. Based on plane wave expansion （PWE） method, the complete photonic band gaps （PBGs） of the novel woodpile three~dimensional （3D） terahertz （THz） photonic crystal （PC） with a decreasing symmetry relative to a face-centred-tetragonal （fct） symmetry are optimized by varying some structural parameters and the highest band gap ratio can reach 27.61%. Compared to the traditional woodpile lattice, the novel woodpile lattice has a wider range of the filling ratios to gain high quality PBGs, which provides greater convenience for the manufacturing process. The novel woodpile 3D PC will be very promising for materials of THz Junctional components.     

用于短波段发光二极管的二维光子晶体禁带研究

运用平面波展开法(PWE),针对光子晶体在短波长段发光二极管(LED)领域上的应用,主要选择高频禁带模式,研究了4种具有较大应用潜力的二维光子晶体结构,包括正方空气柱结构、三角空气柱结构、正方介质柱结构和三角介质柱结构。在不同晶格常数、占空比(AFF)、柱半径和晶格常数比下,分析了TE模式和TM模式光子禁带的变化。数据分析表明,光子禁带中心波长随AFF增加而变小。相比于其他结构,正方介质柱结构更适于短波段光子晶体LED来提高其出光效率,三角介质柱结构和三角空气柱结构适合用于构造短波段偏振光LED。     

二维介电光子晶体中的赝自旋态与拓扑相变

基于背散射抑制且对缺陷免疫的传输性质,光子拓扑绝缘体为电磁传输调控提供了一种新颖的思路.类比电子体系中的量子自旋霍尔效应,本文设计出一种简单的二维介电光子晶体,以实现自旋依赖的光子拓扑边界态.该光子晶体是正三角环形硅柱子在空气中排列而成的蜂窝结构.将硅柱子绕各自中心旋转60°,可实现二重简并的偶极子态和四极子态之间的能带翻转.这两对二重简并态的平均能流密度围绕原胞中心的手性可充当赝自旋自由度,其点群对称性可用来构建赝时间反演对称.根据k·p微扰理论,给出了布里渊区中心附近的有效哈密顿量以及对应的自旋陈数,由此证实能带翻转的实质是拓扑相变.数值计算结果揭示,在拓扑非平庸和平庸的光子晶体分界面上可实现单向传输且对弯曲、空穴等缺陷免疫的拓扑边界态.本文中的光子晶体只由电介质材料组成并且晶格结构简单,实现拓扑相变时无需改变柱子的填充率或位置,只需转动一个角度.因此,这种结构在拓扑边界态的应用中更为有效.     

Huge photonic band gaps with strong attenuations resulted from quasi-one-dimensional waveguide networks composed of triangular fundamental loops

In order to design systems generating large photonic band gaps (PBGs), in this paper we construct interesting quasi-one-dimensional (quasi-1D) periodic triangular, diamond, and tetrahedral networks composed of 1D waveguides and triangular fundamental loops. The optical frequency band structures and photonic attenuation behaviors of electromagnetic (EM) waves propagating in the three kinds of one- and two-segment-connected (1SC and 2SC) networks without dissipation are, respectively, investigated and we find that huge PBGs can be produced in the middle of a frequency period and the widths of the largest PBGs can be controlled by adjusting the matching ratio of waveguide length. When the ratio equals 2:1, the width of the hugest PBG resulted in tetrahedral network reaches 0.73 times of a frequency period and is about 1.16 times of the best result reported previously. The average attenuations of the largest PBGs are very strong and increase rapidly with the increment of the number of unit cell. This makes our designed networks with very few unit cells exhibit wonderful PBG features and they can be realized in experiments easily. It may be useful for the designing of optical devices with large PBG and strong attenuation.     

Graphene based photonic crystal optical filter: Design and exploration of the tunability

Optical characteristics of two new graphene based photonic crystals are studied in detail. A structure containing alternating layers of graphene and SiO₂ slabs is considered as the ideal crystal. The dependency of the photonic band gaps (PBGs) to the dielectric layer thickness and the period number is explored at first step. Potential of the proposed crystal to be used as an optical filter is then investigated. Adding a nonlinear electro-optic polymer as a defect layer, the alterations of the optical features are inspected. Results show that the defect layer insertion causes a resonant mode inside the PBGs. However, the location of the defect layer inside the crystal is very effective on both the frequency and width of the resonant mode. Tunability of the optical features is probed by taking into account of the dependencies to the wave incident angle, graphene chemical potential and the applied external voltage to the defect layer.