大带隙二维三角格子光子晶体结构参数的优化设计

光子晶体结构设计优化是理论研究的一个重要内容.运用平面波展开法对圆柱、方柱及正六边柱构造的二维三角格子光子晶体的禁带进行仿真计算,讨论了介质材料分别为GaAs、Si和Ge情况下,柱子形状、旋转角度、填充比的变化对完全光子禁带的影响.发现:对于二维三角格子光子晶体,相对于介质柱,空气柱更易获得完全光子禁带;而相对于圆柱及...     

The effect of etching interfacial layers on the absolute photonic band gap in two-dimensional photonic crystals

The photonic band structures of two-dimensional (2D) photonic crystals with etched interfacial layers between air rods and the background dielectric is studied theoretically. The effect of etching interfacial layers on absolute photonic band gap (PBG) is analyzed quantitatively. Numerical calculations are carried out based on Maxwell's equations and the plane-wave expansion method. It is shown that the physical property of interfacial layers influence the absolute PBG, and the existence of interfacial layers cannot enlarge the largest absolute PBG of an ideal case without interfacial layers.     

Photonic amorphous diamond structure with a 3D photonic band gap

We report that a full three-dimensional (3D) photonic band gap (PBG) is formed in a photonic amorphous structure in spite of complete lack of lattice periodicity. It is numerically shown that the structure "photonic amorphous diamond" possesses a sizable 3D PBG (18% of the center frequency for Si-air dielectric contrast) and that it can confine light at a defect as strongly as conventional photonic crystals can. These findings present important new insight into the origin of 3D PBG formation and open new possibilities in developing 3D PBG materials.     

Larger absolute photonic band gap in two-dimensional air–silicon structures

We investigate different aspects of the absolute photonic band gap (PBG) formation for two-dimensional photonic crystals, consisting of air rods drilled into silicon. Specifically, square lattices of square and circular rods are considered. The lattice symmetry, shape and orientation of the rods affect the photonic gap parameters. A symmetry reduction by addition of a smaller different shaped rod into the center of the lattice unit cell can produce significantly larger band gap. Combining the symmetry reduction and rotation of the noncircular rods yields the greatest improvements in the size of absolute band gap. We discuss the maximization of the absolute PBG width as a function of lattice parameters and the practical fabrication feasibility of these optimized structures.     

Improvement of absolute band gaps in 2D photonic crystals by anisotropy in dielectricity

Two-dimensional (2D) photonic band gaps (PBG) structure fabricated from anisotropic dielectric is studied by solving Maxwell's equations with use of plane-wave expansion method. Numerical simulations show that absolute photonic band gaps can be substantially improved in two dimensional square and triangular lattices of cylinders by introducing anisotropy in material dielectricity. Owing to different refractive indices for electromagnetic waves with E- and H-polarization, the quasi-independent adjustment of band gaps for the E- and H-polarization modes can be implemented by uniaxial crystals with their extraordinary axis parallel to the cylinders. Large absolute band gaps can be created for uniaxial cylinders in air with a positive anisotropy. In the case of air holes in background uniaxial dielectric with even a weak negative anisotropy, the absolute band gap can be increased 2-3 times. Large absolute band gap can also be obtained in other complex configurations of uniaxial and biaxial materials and this enables a full exploitation of potential utilization for anisotropic materials available in nature. Such a mechanism of band gap adjustment should open up a new scope for designing band gaps in 2D PBG structures. Received 26 January 1999     

基于太极形介质柱六角光子晶体禁带特性研究

提出了一种新型的非对称性散射体的二维六角晶格光子晶体结构–-太极形介质柱光子晶体. 利用平面波展开法从理论研究这种光子晶体结构的能带特性以及结构参数对完全禁带的影响. 研究表明:散射体对称性的打破, TE模和TM模能带宽度和数目都会有所增加, 有益于获得更宽的完全禁带以及更多条完全禁带.通过参数优化, 发现在ε = 17, R=0.38 μm, r=0.36R, θ = 0° 时, 获得最大完全带隙宽度0.0541(ωa/2πc); 在ε = 16, R=0.44, r=0.2R, θ = 0°时, 光子晶体完全带隙数目最多达到8条. 关键词： 光子晶体 禁带 平面波展开     

电磁波在周期介质中的传播及二维光子晶体的光子带结构

光子晶体是光学与凝聚态物理交叉的新领域,也是近年来应用物理学的一个重要研究领域,它是一种由介电常数高的(低的)介质在另一种介电常数低的(高的)背景介质中周期排列所组成的人造多维周期结构材料,能够产生光子带隙。频率落在带隙内的光在晶体里沿任何方向都不能传播,因而具有能够抑制原子、分子的自发辐射等诱人的光电子学特性,在基础研究和实际应用上都有着巨大的潜力。本文在这一领域里进行了富有成效的研究,获得了很好的结果。主要有:(1)利用平面波展开方法来计算二维光子晶体的带隙结构。首先,我们设计正方晶胞的二维光子晶体模型。设x₃方向为介质柱的轴方向,二维周期结构在x₁-x₂平面上。晶胞的晶格常数为a,半径为r,介质柱和空气柱的介电常数分别为ε_a=17和ε_b=1,a>2r。设计的核心思想是通过降低光子晶体结构的对称性,消除光子能带在晶体的布里渊区高对称点上的本征简并。(2)对于二维光子晶体的电磁波理论及周期介质中的Bloch波解做了详细的推导,给出了光子晶体中禁带存在的理论依据。同时以正方格子晶格的二维光子晶体为例,验证了电介质在空气圆孔中的排列存在E偏振和H偏振的光子带隙重叠区,称为绝对光子带隙。对于二维的光子晶体,两种本征偏振模式的光子能带结构可以独立地调节,以实现两者的光子带隙的最优重叠, 从而大大提高了二维光子晶体的完全带隙宽度。     

Controlling the photoluminescence spectroscopy of quinacrine dihydrochloride by SiO_2 inverse opal photonic crystal

Manipulation of the photoluminescence spectra of light-emitting materials doped in three-dimensional （3D） inverse opal photonic crystals is investigated. Quinacrine dihydrochloride molecules doped highly ordered SiO2 inverse opal is successfully synthesized by co-assembly combined with double-substrate vertical infiltrate method. The quinacrine dihydrochloride-doped and-undoped SiO2 inverse opals each exhibit an apparent photonic band gap （PBG） in the visible light region. Significant suppression of the emission is observed when the PBG is overlapped with the quinacrine dihydrochloride emission bands. The mechanism of suppression effect of PBG in inverse opal on the fluorescence intensity of quinacrine dihydrochloride molecules is studied.     

磁导率对二维蜂窝结构光子晶体带隙的影响

利用平面波展开法对二维六角晶格结构磁性光子晶体的带隙特性进行了研究,给出其能带结构分布图,并与非磁性介质构成的光子晶体进行了比较.结果表明,由磁性材料构成的光子晶体更易出现带隙,磁导率对带隙结构影响很大.空气背景磁性散射子情况,磁导率增加较小时,二个绝对光子带隙宽度逐渐减小,直至消失.继续增加磁导率,在较低频率范围内出现一个绝对光子带隙,占空比逐渐加大,且最佳填充系数基本保持不变.磁性背景空气散射子,类似地在较低频率范围内也出现了一个绝对光子带隙.磁性背景非磁性散射子与空气背景磁性散射子情况相似.     

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).     

空气环型二维光子晶体完全带隙特性研究

采用平面波展开法, 系统研究了空气环型二维光子晶体的完全光子带隙随结构参数变化而改变的规律, 并将其与普通的空气孔型和介质柱型二维光子晶体的完全带隙进行了比较. 研究表明: 空气环型二维光子晶体不仅可以获得更宽的完全带隙, 而且, 当介质折射率较低时, 其可以获得普通空气孔型和介质柱型二维光子晶体在低折射率条件下所无法获得的完全带隙. 关键词： 空气环型二维光子晶体 完全带隙 平面波展开法     

Band gap structure of disordered chiral photonic crystals

Based on the non-symmetric transmission-line method, the band gap structure of disordered chiral photonic crystals (CPC) has been investigated. The influence of the chiral parameters, the disorder, the periods and the refractive index on the band gap structure has been discussed. It is found that the photonic band gap (PBG) in CPC is more obvious than that in the conventional photonic crystals, and the PBG can be increased by increasing the periods or the contrast of the refractive index of the two media. It is also found that the existence of disorder will influence the band edge of the PBG, and such influence will increase with the increment of periods or the contrast of the refractive index of the two media.     

Optical properties of a periodic one-dimensional semiconductor-organic photonic crystal in UV region

Optical properties of a one-dimensional semiconductor-organic photonic crystal with periodic AlN/3-octylthiophenes (P3OT) multilayer structure are exhibited and confirmed by a calculation of the transfer matrix method (TMM). An AlN/P3OT multilayer structure displays incomplete photonic band gap behavior in the UV region. The AlN/P3OT multilayers with four pairs of 35-nm-AlN and 35-nm-P3OT layers exhibit a high reflectivity of 89% and less absorption of 10% at a wavelength of about 300 nm. These results demonstrate the AlN/P3OT multilayer structure could be a good candidate for absolute inhibition of reflection in the ultraviolet region for a given orientation.     

Ag-SiO2多层薄膜对光子带隙的影响

采用超高真空电子束蒸发制备了一维紫外、可见光波段光子晶体.研究了在石英衬底上不同周期Ag/SiO2体系对光子带隙的影响.带隙位置与理论计算结果符合.发现二氧化硅层的厚度对带隙位置和银层的透过率有较大影响,厚度的增加降低了反射率,从而使光子带隙更加明显,当厚度达到12层时观察到清晰的光子带隙.     

Analysis of photonic band gaps in a two-dimensional photonic crystal with centrifugal core-shell rods

The absolute photonic band gap (PBG) in two-dimensional (2D) photonic crystal with excentric core-shell rods is studied in this paper. The core rod shifts away from the core-shell rod center, and its position is decided by two new introduced parameters — the shift angle θ and the offset ρ. We use the FDTD algorithm to calculate the photonic bands of the photonic crystal, and analyze how the offset and shift angle affect the photonic bang gap of excentric core-shell photonic crystal for different core rod size. It has been shown that the variation of the photonic band gap is quite peculiar.     

Two-dimensional Si photonic crystals on oxide using SOI substrate

Two-dimensional photonic crystals (2D-PhCs) on oxide can be easily incorporated into photonic integrated circuits. Although an asymmetrical structure (air/PhC/oxide) is advantageous in terms of ease of fabrication, it has been pointed out that such a structure may have no photonic band gap (PBG). To clarify the characteristics of the asymmetrical structure, we calculated the band structure using the three-dimensional (3D) FDTD method and measured the transmission characteristics of a fabricated 2D Si-PhC on oxide. The calculations show that we can use a quasi-PBG even in an asymmetrical structure when the PhC thickness satisfies the single-mode condition. The measured transmission characteristics correspond to the calculated band structure and reveal the existence of a quasi-PBG. These results show that the asymmetrical 2D Si-PhC-on-oxide structure can be applied to various optical devices.     

Complete photonic band gaps in one-dimensional ternary photonic crystals containing single negative materials

Complete photonic band gaps (PBGs) are found in one-dimensional ternary photonic crystals (1D TPCs) composed of an ordinary dielectric and single negative metamaterials. The proposed TPC gives omni directional PBG completely independent of polarizations dependent weekly on angle of incidence. Here the choice of different parameters of TPC is done in such a way so that it eliminates the Brewster's-angle transmission resonance, thus allowing a complete 3D PBG. It exhibits a photonic band or gap near frequencies where either the magnetic permeability or the electric permittivity of the metamaterial changes sign, whose width increases with the increasing angle of incidence. These result from the dispersive properties of the metamaterials and disappear for the particular case of propagation along the stratification direction. The results are discussed in terms of incident angle, layer thickness, dielectric constant of the dielectric material for TE and TM polarizations.     

The rapid preparation of large-scale CdS opal photonic crystals and study of the optical properties

Monodispersed silica microspheres of 270 nm are synthesized by a colloidal solution method. Larger scale perfect three-dimensional photonic crystals (PCs) are rapidly prepared using the evaporation of acetone to self-assemble the microspheres on quartz substrates by vertical deposition methods. We find that the pseudo-photonic band gap (PBG) of the PC structure changes with increasing annealing temperature; it drastically shifts from 450 nm for as-grown crystals to 409 nm for annealing at 800 °C. CdS photonic crystals are formed by infiltrating CdS nanocrystals of 6 nm into the SiO₂ PC structure. The transmission and spontaneous emission characteristics of CdS PCs have been investigated. The clear dip in the spontaneous emission spectrum relates to the photonic band gap of CdS PCs, indicating that the spontaneous emission is inhibited in the region of the PBG. The emission band of CdS PCs becomes narrower and sharper than that of CdS nanocrystals; this demonstrates that the emission band and intensity of the luminescent devices will be tuned by controlling the position of the PBG. PACS 42.70.Qs; 42.25.Bs; 78.20.-e; 78.55.Et     

基于横向磁光效应磁化等离子体光子晶体的光子带隙特性

通过外加与电磁波传播方向垂直的磁场来调控等离子体光子晶体的光子带隙结构。采用时域有限差分方法数值分析了由本征层为等离子体层和其他电介质材料层交替堆叠而成的磁化等离子体光子晶体的光子带隙结构和频谱特性。数值结果表明,光子晶体中等离子体的介电常数随着外磁场大小的变化而改变,从而使磁化等离子体光子晶体的带隙特性在一定的频率范围相应地得到调节。     

Photonic band gap grating in He+-implanted lithium niobate waveguides

In this work, we report the investigation of 2D photonic crystals in lithium niobate associated with waveguiding structures fabricated by He⁺ implantation. From the material point of view, the investigation of PBG structures in lithium niobate is of great interest for optoelectronics technology since this crystal is one of the most important materials widely used in integrated and non linear optics. The choice of the implantation technique to produce the waveguide is motivated by the possibility of having both Transverse Electric (TE) and Transverse Magnetic (TM) guided modes in order to obtain a total photonic band gap (PBG).