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1.
Photonic band structures of annular photonic-crystal (APC) silicon-on-insulator (SOI) asymmetric slabs with finite thickness were investigated by the three-dimensional plane-wave expansion method. The results show that for a broad range of air-volume filling factors, APC slabs can exhibit a significantly larger bandgap than conventional circular-hole photonic-crystal (PC) slabs. Bandgap enhancements over conventional air hole PC SOI slabs as large as twofold are predicted for low air-volume filling factors below 15%. This desirable behavior suggests a potential for APC SOI slabs to serve as the basis of various optical cavities, waveguides, and mirrors. 相似文献
2.
Kurt H Hao R Chen Y Feng J Blair J Gaillot DP Summers C Citrin DS Zhou Z 《Optics letters》2008,33(14):1614-1616
We present the design of realistic annular photonic-crystal (APC) structures of finite thickness aiming to obtain a complete photonic bandgap (PBG). The APC is composed of dielectric rods and circular air holes in a triangular lattice such that each rod is centered within each hole. The optical and geometrical values of the structure are studied, and the interplay between various design parameters is highlighted. The coupled role of the inner-dielectric-rod radius, material types, and slab thickness is investigated. It is shown that the slab thickness is vital to obtain a complete photonic bandgap below the light line, and the specific value of the inner-dielectric-rod radius to sustain the maximum PBG if the hole radius is fixed at proper value is found. 相似文献
3.
The polarization-dependent photonic band gaps (TM and TE polarizations) in two-dimensional photonic crystals with square lattices
composed of air holes in dielectric and vice versa i.e., dielectric rods in air, using the plane-wave expansion method are investigated. We then study, how the photonic band
gap size is affected by the changing ellipticity of the constituent air holes/dielectric rods. It is observed that the size
of the photonic band gap changes with changing ellipticity of the constituent air holes/dielectric rods. Further, it is reported,
how the photonic band gap size is affected by the change in the orientation of the constituent elliptical air holes/dielectric
rods in 2D photonic crystals. 相似文献
4.
I. Costa P. L. Almeida D. Filip J. L. Figueirinhas M. H. Godinho 《Opto-Electronics Review》2006,14(4):299-303
In this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) that were used for assembling
electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced
by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In
order to eliminate and control these textures we used a process similar to that introducted in literature [1] which consists
of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions
in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and
stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by
optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used
to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic
liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells
were obtained. 相似文献
5.
《中国科学:物理学 力学 天文学(英文版)》2010,(10)
Absolute band gaps of a two-dimensional triangular-lattice photonic crystal are calculated with the finite-difference time-domain method in this paper.Through calculating the photonic band structures of the triangular-lattice photonic crystal consisting of Ge rods immersed in air with different shapes,it is found that a large absolute band gap of 0.098 (2c/a) can be obtained for the structures with hollow triangular Ge rods immersed in air,corresponding to 19.8% of the middle frequency.The influence of the different factors on the width of the absolute band gaps is also discussed. 相似文献
6.
《Superlattices and Microstructures》1996,20(2):207-211
The electrical current of porous silicon (PS) has been measured while several treatments are made to the samples. When the samples are exposed to air, the DC current increases or decreases depending on the surface conditions of the samples. These results, found to be caused by water vapors in air, can be explained based upon the adsorbate-induced surface band bending. Photon soaking in air alters the direction of current change after air exposure and Fourier Transform Infrared Spectra show a redistribution of surface adsorbates after photon soaking in air. This indicates that photon soaking in air can cause a change in the band bending on the surface of PS. 相似文献
7.
采用平面波展开法模拟二维光子晶体在E极化和H极化下的能带结构,研究Ge基二维正方晶格光子晶体的填充比以及晶格排列结构对最大禁带宽度的影响。结果表明:在空气背景材料中填充Ge柱的介质柱结构中,可产生TE、TM带隙,且各方向完全带隙出现在r/a=0.19~0.47范围内,最大完全帯隙禁带宽度可以达到0.064(归一化频率);在选取Ge为背景材料的空气孔型结构中,同样可产生TE、TM带隙,且各方向完全带隙出现在r/a=0.46~0.49范围内,最大完全帯隙禁带宽度可以达到0.051(归一化频率)。同时,不论在介质柱型还是空气孔型结构中,带隙宽度都随着r/a的增大呈先增大后减小的趋势。 相似文献
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9.
We analyze the absolute photonic band gap in two dimensional (2D) square, triangular and honeycomb lattices composed of air holes or rings with different geometrical shapes and orientations in anisotropic tellurium background. Using the numerical plane wave expansion method, we engineer the absolute photonic band gap in modified lattices, achieved by addition of circular, elliptical, rectangular, square and hexagonal air hole or ring into the center of each lattice unit cell. We discuss the maximization of absolute photonic band gap width as a function of main and additional air hole or ring parameters with different shapes and orientation. 相似文献
10.
A polarizing beam splitter (PBS) and a non-polarizing beam splitter (NPBS) based on a photonic crystal (PC) directional coupler are demonstrated. The photonic crystal directional coupler consists of a hexagonal lattice of dielectric pillars in air and has a complete photonic band gap. The photonic band structure and the band gap map are calculated using the plane wave expansion (PWE) method. The splitting properties of the splitter are investigated numerically using the finite difference time domain (FDTD) method. 相似文献
11.
采用平面波展开法数值计算了空气背景中由圆形、正六边形和正方形介质柱构造的二维三角晶格光子晶体禁带结构,并研究了介质方柱旋转角度、介质折射率和填充比对完全光子禁带宽度的影响.结果表明,在低频区,介质方柱旋转17°时,出现最大完全光子禁带,且最大禁带宽度随介质折射率的变化较为稳定.在高频区,介质方柱旋转30°时,完全光子禁带宽度最大;且介质材料折射率n=2.2时即出现完全光子禁带,n=2.6时,完全光子禁带达到最大. 相似文献
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与介质柱型光子晶体相比,空气孔光子晶体更易于制作和集成而更有应用价值.采用平面波展开法证实了填充液晶的二维三角形分布的空气孔光子晶体方向能隙的可调节性.数值模拟结果表明:1)通过外界电场控制空气孔中所填充的相列液晶的方向可以对光子晶体的方向能隙进行调节,这种可调节性可用于制作场敏偏光片.这与Liu等人研究介质柱型光子晶体的结论相类似;2)用phenylacetylene型液晶替代5CB液晶作为填充物质所得到的空气孔光子晶体偏光片可使用的频率范围显著增大.在此基础上,还研究了填充液晶的光子晶体波导传输谱线的可调节性对特定波长的光切断和开通控制的原理,实现了与以往光开关原理不同的光子晶体光开关.
关键词:
光子晶体
液晶
可调节性
平面波展开法
场敏偏光片 相似文献
15.
局部空气放电是导致高压输变电设备绝缘劣化的重要因素。空气放电中丰富的发射光谱信息与放电特征存在直接映射关系。采用针-板电极模拟了空气电晕放电的发展过程,并检测了放电由弱变强过程中的“紫外-可见光-近红外”波段在200~980 nm范围内的发射光谱。放电初期的发射光谱主要由氮气分子N2的带状光谱组成,分别为N2第二正带系(second positive system, SPS)和N2第一正带系(first positive system, FPS)。放电程度加深后,发生能级跃迁的粒子种类更加丰富,由此产生了带状光谱与线状光谱相互交叠的复杂谱线,光谱范围也由放电初期的280~460 nm扩展至200~980 nm。放电处于临界击穿时,发射光谱的强度急剧增加,强度最高值出现在500.715和777.202 nm处,分别对应氮离子N+和氧原子O的辐射谱线,这意味着微观放电过程再次发生改变。基于空气放电机理分析得到:放电初期、放电加深、放电临界击穿三个阶段中强度占优的谱峰或谱带分别由N2... 相似文献
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描述在Si基底上制备带隙在近红外波段部分空气桥式二维光子晶体(PC).选用HF酸溶液作为腐蚀液,利用聚焦离子束刻蚀技术直接刻蚀出具有三角形空气洞结构的二维PC,并测出了二维PC完整的第一带隙透过谱的带隙范围为123—155μm.实验测得的透过谱与理论计算的空气桥式二维PC的计算结果一致.类TM0模的存在减小了带隙的宽度.由于部分SiO2支撑桥式平板,二维PC易于按所需尺寸进行制备.同时,通过改变平板下的支撑材料,可以制出有源的PC,利用这种机理可以把光从支撑材料中引出.
关键词:
二维光子晶体
带隙
平板波导 相似文献
18.
The hierarchical phononic crystals to be considered show a two-order “hierarchical” feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation. 相似文献
19.
Zhi-Yuan Li Ben-Yuan Gu Guo-Zhen Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):65-73
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 相似文献
20.
在氩气和空气混合气体介质阻挡放电中,首次发现了团簇六边形斑图。运用发射光谱法,研究了此斑图中单个团簇的三种等离子体参数:分子振动温度、分子转动温度以及电子的平均能量随空气含量的变化。实验通过测量氮分子光谱并采用氮分子第二正带系(C3Πu→B 3Πg)计算了振动温度;同时采集氮分子离子(N+2)的第一负带系(B 2Σ+u→X 2Σ+g)计算转动温度。利用氮分子离子391.4 nm和激发态的氮分子337.1 nm两条发射谱线的相对强度之比,作为研究电子平均能量的变化的依据。结果显示,当混合气体中空气含量从16%逐渐增大到24%时,三种等离子体参数均逐渐增大。 相似文献