Ultrasmall-angle X-ray scattering analysis of photonic crystal structure

The results of an ultrasmall-angle X-ray scattering study of iron(III) oxide inverse opal thin films are presented. The photonic crystals examined are shown to have fcc structure with amount of stacking faults varying among the samples. The method used in this study makes it possible to easily distinguish between samples with predominantly twinned fcc structure and nearly perfect fcc stacking. The difference observed between samples fabricated under identical conditions is attributed to random layer stacking in the self-assembled colloidal crystals used as templates for fabricating the inverse opals. The present method provides a versatile tool for analyzing photonic crystal structure in studies of inverse opals made of various materials, colloidal crystals, and three-dimensional photonic crystals of other types.     

聚焦离子束研制半导体材料光子晶体

介绍了利用聚焦离子束设备在多种半导体材料上成功研制的近红外波段二维光子晶体，给出了相关微加工结果，发现微加工的尺寸和理论设计尺寸相吻合；测试了所加工的无源光子晶体光子带隙和有源光子晶体的发光谱. 实验证明聚焦离子束可以研制二维光子晶体及相关光子晶体器件. 关键词： 聚焦离子束 半导体材料 光子晶体     

半导体量子阱材料微加工光子晶体的光学特性

利用聚焦离子束刻蚀方法和电子束制版结合干法刻蚀方法制备了二维近红外波段光子晶体，发现两种方法都可以制备出均匀的二维光子晶体，聚焦离子束方法操作简单，电子束制版结合干法刻蚀方法操作步骤复杂.光谱测试表明，利用聚焦离子束方法在有源材料上刻蚀的光子晶体不发光，而电子束制版结合干法刻蚀方法制备的小晶格常数光子晶体即使有些无序，其出光效率也提高到没有光子晶体时的两倍.对两种方法所加工的光子晶体不发光和提高出光效率的机理进行了分析. 关键词： 聚焦离子束 电子束制版 光子晶体 出光效率     

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.     

光子晶体表面结构的改变对成像的影响

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.硅材料以其良好的物理性质成为当今集成光学领域中应用最广的材料之一.本文以硅介质柱在空气中周期性排列构成六角结构的光子晶体平板为例,运用平面波展开法进行光子晶体能带计算并运用时域有限差分法模拟改变光子晶体平板成像并讨论表面结构对成像的影响.光子晶体平板等效折射率为-1时,通过改变上下侧最外层介质柱的半径或是侧向移动最外层介质柱发现:当光子晶体平板表面结构发生改变时光子晶体平板仍能成像但像点强度发生变化.当光子晶体平板表面结构的改变在一定范围时,所成像的位置发生改变且位置变化符合光子晶体成像经典的Veselago关系;当光子晶体表面结构的变化超过该范围时,所成像与物的相位发生反相同时像点位置发生"巨变",此时Veselago关系已不成立.数值模拟表明:光子晶体平板表面结构的改变可以有效地改变该光子晶体平板所成像的强度、位置和相位.     

The effect of random variations of structure parameters on photonic band gaps of one-dimensional plasma photonic crystals

The electromagnetic properties of one-dimensional plasma photonic crystals influenced by random perturbation of structure parameters are studied through transfer matrix method in the paper. The random perturbation of thicknesses of layers as well as plasma frequency of layers can influence the electromagnetic properties of one-dimensional plasma photonic crystal. The random perturbation of thicknesses of layers tremendously impacts the band structure of one-dimensional plasma photonic crystals in high frequency domain. The random perturbation of plasma frequency, however, contributes to the moving of a cutoff frequency in the low frequency domain. The position of the defect mode of one-dimensional plasma photonic crystal randomly moves due to the random perturbations. The effect of random perturbation of plasma frequency is more significant than that of random perturbation of thickness of layers, which alters not only the transmittance but also the position of the defect mode. An improved quality factor and a shortened moving distance of the defect mode are both acquired by increasing the period number. And then this work may provide a crude but useful instrument in analyzing disordered 1DPPCs.     

聚甲基丙烯酸甲酯光子晶体的生长和结构分析

金属/半导体基光子晶体有重大的国防应用价值,其生长技术的核心是设计合适的方法将聚甲基丙烯酯甲酯(PMMA)微球组装成光子晶体。在目前垂直沉积法的基础上,通过控制甲基丙烯酸甲酯(MMA)和偶氮引发剂的反应,使用等温蒸发工艺开发了光子晶体的可控垂直沉积(CVD)技术。实验合成了高度单分散的PMMA微球,并将PMMA微球组装成了光子晶体;对试样进行扫描电镜研究发现,晶体内部排列有序度很高,表面层很完美平整,在3μm×5μm的有序区内仅有两个点缺陷;使用直径分别为294nm和345nm的PMMA微球,沉积出具有规则的周期性密堆积结构的光子晶体,试样的完美有序区范围在20μm以上。实验发现,在可控垂直沉积法的晶体生长过程中,光子晶体的生长方式为连续生长,生长界面为粗造界面。     

Propagation of an X‐ray beam modified by a photonic crystal

A method of calculating the transmission of hard X‐ray radiation through a perfect and well oriented photonic crystal and the propagation of the X‐ray beam modified by a photonic crystal in free space is developed. The method is based on the approximate solution of the paraxial equation at short distances, from which the recurrent formula for X‐ray propagation at longer distances is derived. A computer program for numerical simulation of images of photonic crystals at distances just beyond the crystal up to several millimetres was created. Calculations were performed for Ni inverted photonic crystals with the [111] axis of the face‐centred‐cubic structure for distances up to 0.4 mm with a step size of 4 µm. Since the transverse periods of the X‐ray wave modulation are of several hundred nanometres, the intensity distribution of such a wave is changed significantly over the distance of several micrometres. This effect is investigated for the first time.     

窄禁带光子晶体能态密度的研究

利用平面波展开法研究了窄禁带光子晶体材料的能态密度分布情况,得到了窄禁带材料构成的三角晶格光子晶体能态密度随着介电常数差值的增大而增大,并且分析了氮化镓在f=0.3时,能态密度分布最小,出现最大光子带隙。研究结果为窄禁带光子晶体器件的构造提供理论依据。     

On the theory of diffraction of light in photonic crystals with allowance for interlayer disordering

Electrodynamic Green’s functions are used to construct an analytical theory of the Bragg diffraction of polarized light in photonic crystals having a close-packed structure. For opal-based photonic crystals, the Bragg diffraction intensity is calculated with allowance for permittivity periodic modulation and for the presence of an optical crystal boundary and interlayer disordering, which usually appears during sample growth. A comprehensive study is made of the effect of the structure disorder caused by the random packing of growth layers on diffraction. For a random constructed twinned fcc structure, the average structure factor and the scattering (diffraction) cross sections (which are dependent on the linear polarization of the incident and scattered waves) are calculated. Numerical examples are used to show that the theory developed can be applied to analyze and process experimental diffraction patterns of real photonic crystals having a close-packed structure disordered in one direction.     

A method of designing photonic crystal grating slow-wave circuit for Ribbon--Beam microwave travelling wave amplifiers

A method of designing a photonic crystal grating slow-wave circuit in which the cylinders of the 2D photonic crystals dot on a cross-sectional plane is established by calculating the band structures of the 2D photonic crystals, and the eigenfrequency of the equivalent waveguide grating. For calculating the band structures, the eigenvalue equations of the photonic crystals in the system of photonic crystal grating slow-wave circuit are derived in a special polarization mode. Two examples are taken to show the method. The design result is validated by the scattering parameters of the same circuit. The result indicates that there exists no photonic band gap if the metal gratings do not extend into the photonic crystals; the design of the circuit without the metal gratings extending into the photonic crystals is less flexible than that with the metal gratings extending into the photonic crystals.     

含特异材料一维超导光子晶体的带隙特性研究

利用传输矩阵法研究了含特异材料的一维超导光子晶体的带隙特性. 研究表明, 这类超导光子晶体同样具有由传统的电介质材料构成的超导光子晶体一样的低频带隙, 且在一定的参数下该低频带隙可以相当宽. 但在一定的结构参数下, 这类超导光子晶体同完全由传统的电介质构成的光子晶体一样不存在低频带隙. 还就超导光子晶体的偏振特性、光子晶体结构参数及环境温度的变化对光子带隙结构的影响进行了研究. 关键词： 超导光子晶体 传输矩阵法 特异材料 光子带隙     

Extrinsic optical scattering loss in photonic crystal waveguides: role of fabrication disorder and photon group velocity

Formulas are presented that provide clear physical insight into the phenomenon of extrinsic optical scattering loss in photonic crystal waveguides due to random fabrication imperfections such as surface roughness and disorder. Using a photon Green-function-tensor formalism, we derive explicit expressions for the backscattered and total transmission losses. Detailed calculations for planar photonic crystals yield extrinsic loss values in overall agreement with experimental measurements, including the full dispersion characteristics. We also report that loss in photonic crystal waveguides scales inversely with group velocity, at least, thereby raising serious questions about future low-loss applications based on operating frequencies that approach the photonic band edge.     

光子晶体能态密度的电磁场特性

基于时域有限差分法,以半导体材料CdSe和CdTe构成二维三角晶格光子晶体,数值模拟了它们的光子晶体能态密度电磁场特性。结果表明,CdSe和CdTe构成二维三角晶格光子晶体具有较好的光子带隙,形成的带隙宽度随介电常数差值的增大而增大。研究结果为光子晶体器件的开发提供参考。     

Tunable lightwave propagation in two-dimensional hole-type photonic crystals infiltrated with nematic liquid crystal

Photonic crystals have many potential applications because of their ability to control lightwave propagation. We have investigated the tunability of lightwave propagation in two-dimensional hole-type photonic crystal structures. The linear waveguides can be obtained by the infiltration of liquid crystals into air holes in hole-type photonic crystal with square lattices. The refractive indices of liquid crystals can be changed by rotating the directors of liquid crystals. Therefore, we can control the lightwave propagation in two-dimensional hole-type photonic crystal structures. Such a mechanism of lightwave adjustment should open up a new application for designing components in photonic integrated circuits.     

Negative refraction in two-dimensional photonic crystals

We present some of our recent results for negative refraction in photonic crystals. The concept of negative refraction in photonic crystals is firstly introduced. Then, the propagation of electromagnetic waves in photonic crystals is systematically studied. By the layer Korringa–Kohn–Rostoker method, the coupling efficiency between external plane waves and the Bloch waves in photonic crystals is investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air with n=1 and a photonic crystal with effective index n_eff=-1. It is also shown that, for point imaging by a photonic crystal slab, owing to the negative refraction, the influence of the surface termination on the transmission and the imaging quality is significant. Finally, we present results experimentally demonstrating negative refraction in a two-dimensional photonic crystal at optical communication wavelengths. PACS 42.70.Qs; 41.85.Ct; 42.30.Va     

Fabrication of Colloidal Photonic Crystals with Heterostructure by Spin-Coating Method

Colloidal photonic crystal heterostructures, composed of two opaline photonic crystal films of silica spheres with different diameters, are fabricated by a two-step spin-coating method. Scanning electron microscopy （SEM） and UV-vis spectrophotometer are used to characterize the heterostructures. The SEM images show good ordering of the two-layer colloidal crystals constituting the heterostructures. The transmission spectra measured from the （111） plane in the heterostructure show that the composite colloidal photonic crystals have double photonic stop bands. Furthermore, when the sizes of the silica spheres used for fabricating the composite photonic crystal are slightly different, the transmission spectrum shows that the composite photonic crystals have more extended bandgap than that of the individual photonic crystals due to partial overlapping of its two photonic stop bands.     

Electromagnetic modes in semi-infinite photonic crystals

In a real photonic crystal, there exist three modes: propagation mode, evanescence mode and surface mode. Using ideal modal, semi-infinite photonic crystals, we study their effects on the transmission spectrum of photonic crystals, respectively. Because there exists only one air–crystal interface in a semi-infinite photonic crystal, no multiple reflection occurs and no evanescent modes and backward-propagating modes exist in this structure. The effects of the evanescence modes are studied by comparing the transmission spectrum of a finite-thickness photonic crystal slab and that of a semi-infinite photonic crystal. In addition, the effects of the backward-propagating modes are investigated using a coated semi-infinite photonic crystal structure. Finally, we study the effects of the surface modes, and find that the transmission spectrum of a semi-infinite photonic crystal is strongly dependent on its termination.     

Two-color light-emitting diodes with polarization-sensitive high extraction efficiency based on graphene

In the present study, graphene photonic crystals are employed to enhance the light extraction efficiency(LEE) of two-color, red and blue, light-emitting diode(LED). The transmission characteristics of one-dimensional(1D) Fibonacci graphene photonic crystal LED(FGPC-LED) are investigated by using the transfer matrix method and the scaling study is presented. We analyzed the influence of period, thickness, and permittivity in the structure to enhance the LEE. The transmission spectrum of 1D FGPC has been optimized in detail. In addition, the effects of the angle of incidence and the state of polarization are investigated. As the main result, we found the optimum values of relevant parameters to enhance the extraction of red and blue light from an LED as well as provide perfect omnidirectional and high peak transmission filters for the TE and TM modes.     

液晶光子晶体的负折射特性研究

可调光子晶体由于其潜在的应用价值成为现今光子晶体研究中的一个热点.本文提出了通过光诱导液晶来调节光子晶体负折射效应的方法,采用平面波展开法、等频图分析法和推广的斯涅尔定理分析了二维液晶正方晶格光子晶体负折射的可调节性.提出了一种新型的液晶光子晶体结构, 数值模拟结果表明:通过偏振光改变液晶指向矢可以调节该液晶光子晶体的负折射.与电场调制方法相比,该光控液晶取向技术具有响应速度快、结构简单的优点.这种可调光子晶体可用于制作光控路由或者应用于全光网络.