Strain effects and phase transitions in photonic resonator crystals

Optical structures with periodic variations of the dielectric constant in one or more directions (photonic crystals) have been employed extensively for studying optical diffraction phenomena. Practical interest in such structures arises from the possibilities they offer for tailoring photon modes, and thereby the characteristics of light propagation and light-matter interactions. Photonic resonator crystals comprising two-dimensional arrays of coupled optical microcavities have been fabricated using vertical-cavity surface-emitting laser wafers. In such structures, the light propagates mostly normal to the periodic plane. Therefore, the corresponding lateral Bragg-periodicities are larger, a feature that is advantageous for device manufacture as it allows for larger lattice constants in the lateral direction. Here we investigate strain effects in a photonic resonator crystal by shifting neighbouring lattice rows of microcavities in opposite directions, thereby introducing an alternating square or quasi-hexagonal pattern of shear strain. We find that, for strain values below a critical threshold, the lasing photon mode is virtually locked to the corresponding mode supported by the unstrained photonic crystal. At the critical strain value, we observe a phase-transition-like switching between the square and quasi-hexagonal lattice modes. The tolerance of subcritical strains suggests that the resonator crystal may be useful for applications requiring high spatial coherence across the lattice, while the mode switching could potentially be exploited in free-space optical communications.     

Large-scale synthesis of a silicon photonic crystal with a complete three-dimensional bandgap near 1.5 micrometres

Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 microm, produced by growing silicon inside the voids of an opal template of dose-packed silica spheres that are connected by small 'necks' formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.     

Electrophoretic assembly of colloidal crystals with optically tunable micropatterns

The production of materials with micrometre- and submicrometre-scale patterns is of importance in a range of applications, such as photonic materials, high-density magnetic data storage devices, microchip reactors and biosensors. One method of preparing such structures is through the assembly of colloidal particles. Micropatterned colloidal assemblies have been produced with lithographically patterned electrodes or micromoulds. Here we describe a different method that combines the well-known photochemical sensitivity of semiconductors with electric-field-induced assembly to create ordered arrays of micrometre-sized colloidal particles with tunable patterns. We show that light affects the assembly processes, and demonstrate how to produce patterns using electrophoretic deposition in the presence of an ultraviolet (UV) illumination motif. The distribution of current across an indium tin oxide (ITO) electrode can be altered by varying the illumination intensity: during the deposition process, this causes colloidal particles to be swept from darkened areas into lighted regions. Illumination also assists in immobilizing the particles on the electrode surface. Although the details of these processes are not well understood, the patterning effects of the UV light are discussed in terms of alterations in the current density that affects particle assembly on an ITO electrode.     

非线性光子晶格的制作及光传输现象研究

采用数值和实验方法研究了非线性光子晶格图样的形成规律及光传输现象。采用光束传输法(BPM)模拟研究光波在由干涉图样及非线性作用下形成的光子晶格中的导光现象。通过多光束干涉观察了干涉图样,并由此制作了光子晶格。研究结果为利用非线性效应制作周期性光子晶格和准周期性光子晶格,并以此实现导光功能提供了新的思路和方法。     

Trapping and emission of photons by a single defect in a photonic bandgap structure

By introducing artificial defects and/or light-emitters into photonic bandgap structures, it should be possible to manipulate photons. For example, it has been predicted that strong localization (or trapping) of photons should occur in structures with single defects, and that the propagation of photons should be controllable using arrays of defects. But there has been little experimental progress in this regard, with the exception of a laser based on a single-defect photonic crystal. Here we demonstrate photon trapping by a single defect that has been created artificially inside a two-dimensional photonic bandgap structure. Photons propagating through a linear waveguide are trapped by the defect, which then emits them to free space. We envisage that this phenomenon may be used in ultra-small optical devices whose function is to selectively drop (or add) photons with various energies from (or to) optical communication traffic. More generally, our work should facilitate the development of all-optical circuits incorporating photonic bandgap waveguides and resonators.     

Free-standing mesoporous silica films with tunable chiral nematic structures

Chirality at the molecular level is found in diverse biological structures, such as polysaccharides, proteins and DNA, and is responsible for many of their unique properties. Introducing chirality into porous inorganic solids may produce new types of materials that could be useful for chiral separation, stereospecific catalysis, chiral recognition (sensing) and photonic materials. Template synthesis of inorganic solids using the self-assembly of lyotropic liquid crystals offers access to materials with well-defined porous structures, but only recently has chirality been introduced into hexagonal mesostructures through the use of a chiral surfactant. Efforts to impart chirality at a larger length scale using self-assembly are almost unknown. Here we describe the development of a photonic mesoporous inorganic solid that is a cast of a chiral nematic liquid crystal formed from nanocrystalline cellulose. These materials may be obtained as free-standing films with high surface area. The peak reflected wavelength of the films can be varied across the entire visible spectrum and into the near-infrared through simple changes in the synthetic conditions. To the best of our knowledge these are the first materials to combine mesoporosity with long-range chiral ordering that produces photonic properties. Our findings could lead to the development of new materials for applications in, for example, tuneable reflective filters and sensors. In addition, this type of material could be used as a hard template to generate other new materials with chiral nematic structures.     

光子晶体及其应用研究

对光子晶体的性质和应用,如光局域化或光子晶体波导,甚至于是沿着一个很尖锐的弯曲的光子晶体波导能力,以及光子晶体激光器,进行了讨论.在这一技术领域,有许多基础方面的特点被认为是正确的,但却没有给出严格的证明.这是由于下列两方面的原因,第一是这个新领域发展的非常迅速,第二是由于在光子晶体中分析电磁波是很困难的,除了使用计算机去得到定量结果外,没有别的选择.板型的光子晶体(带有一个周期性空洞系统的高折射率板片),对高集成的光电路器件来说,也许是最佳结构.     

微波光子滤波器

微波光子滤波器能够实现在光域内直接对射频信号的处理,并且较易实现可调谐性和传输函数的快速重构,从而成为微波光子学的一个重要研究内容.本文综合评述了不同光源的微波光子滤波器和基于FBG的不同微波光子滤波器结构,并分析比较了各自的功能特点和不足.     

一维光子晶体带隙结构研究

光子晶体材料的介电常数在空间中呈周期分布，这种材料存在光子带隙，引入缺陷对光有局域效应，为更好地控制光和利用光提供了新的方法。文章利用传输矩阵法计算了一维光子晶体不同结构的带隙特征，计算表明光子带隙的宽度受到材料介电常数及介质层厚度的影响。随材料介电常数及介质层厚度的增加，光子带隙宽度存在一个极大值，对于确定材料构成的光子晶体，两介质等厚时带隙最宽。     

Microperiodic structures: direct writing of three-dimensional webs

Applications are emerging that require the creation of fine-scale structures in three dimensions--examples include scaffolds for tissue engineering, micro-fluidic devices and photonic materials that control light propagation over a range of frequencies. But writing methods such as dip-pen nanolithography and ink-jet printing are either confined to two dimensions or beset by wetting and spreading problems. Here we use concentrated polyelectrolyte inks to write three-dimensional microperiodic structures directly without using masks. Our technique enables us to write arbitrary three-dimensional patterns whose features are nearly two orders of magnitude smaller than those attained with other multilayer printing techniques.     

Low-loss hollow-core silica/air photonic bandgap fibre

Photonic bandgap structures use the principle of interference to reflect radiation. Reflection from photonic bandgap structures has been demonstrated in one, two and three dimensions and various applications have been proposed. Early work in hollow-core photonic bandgap fibre technology used a hexagonal structure surrounding the air core; this fibre was the first demonstration of light guided inside an air core of a photonic bandgap fibre. The potential benefits of guiding light in air derive from lower Rayleigh scattering, lower nonlinearity and lower transmission loss compared to conventional waveguides. In addition, these fibres offer a new platform for studying nonlinear optics in gases. Owing largely to challenges in fabrication, the early air-core fibres were only available in short lengths, and so systematic studies of loss were not possible. More recently, longer lengths of fibre have become available with reported losses of 1,000 dB km(-1). We report here the fabrication and characterization of long lengths of low attenuation photonic bandgap fibre. Attenuation of less than 30 dB km(-1) over a wide transmission window is observed with minimum loss of 13 dB km(-1) at 1,500 nm, measured on 100 m of fibre. Coupling between surface and core modes of the structure is identified as an important contributor to transmission loss in hollow-core photonic bandgap fibres.     

Quantum coherent control of ultrashort laser pulses

The effective photonic control is one of the key issues in photo-physics. Significant advancement in photonic crystals, quantum optics, ultrafast optics as well as micro-nano-optics gives rise to new op-portunities to manipulate the emission and propagation in optical fields, leading to a number of new and interesting discoveries, e.g., ultrashort light pulse storage and efficient energy conversion. This paper reviews the latest research progress in storage, release and energy conversion for ultrashort laser pulses in periodical arrays of absorbing medium. Techniques to fabricate such devices are also presented.     

粘质沙雷氏菌(Serratia marcescens)研究Ⅱ--营养基质和不同色光对粘质沙雷氏菌生长的影响

粘质沙雷氏菌(Serratia marcescens)9-1、9-2、16-1 3菌株,在牛肉膏蛋白胨培养基上生长很好,产生红色菌落. 它们都利用乳糖、D-半乳糖、L-( )阿拉伯糖、鼠李糖、葡萄糖、蔗糖、D-山梨醇,生长良好并产生红色色素;在硫酸铵、L-赖氨酸、尿素、酪蛋白水解物、DL-天门冬酰胺、胰蛋白胨为氮源的培养基上生长得好并产生红色色素,而在硝酸铵、硝酸钠为氮源的培养基上则生长差和产生粉红色色素;Na^ 、K^ 、PO3^-4、Ca^2 、Mg^2 等元素对这3菌株的生长和产生红色色素有一些影响;白色光有促进生长和红色色素的产生,绿色光和黄色光对生长和红色色素产生则有不良影响.     

二维函数光子晶体中的类Dirac点及带隙结构

设计一种二维函数光子晶体, 该光子晶体仅需通过改变外加的光强分布或电场分布, 即可改变其介质柱介电常数的函数形式, 从而获得所需的带隙结构. 选取不同介质柱半径及不同介电常数函数形式的二维函数光子晶体结构, 通过数值计算得到类Dirac点和带隙结构, 所得结论可为光学器件的设计提供理论依据.     

利用Z型载流导线列阵构成的新型磁晶格

提出两种新型的磁表面微囚禁列阵来构成一维和二维的磁晶格，计算了载流导线和偏磁场形成的磁场强度、梯度和曲率分布．研究表明这些磁表面微囚禁列阵微阱中心的磁场存在非零最小值，可以用来作成一维和二维的磁晶格，实现多维BEC列阵，甚至是光子晶体．     

光子晶体的能带理论

光子晶体具有光子能带,并且光子能带可能存在光子禁带。我们通过运用光子晶体的能带和禁带理论.就能够控制光在晶体中的传播。光子晶体对光子有着特殊的物理性质,它在光传输和光学器件有着广泛的用途。本文主要概述了光子晶体的概念、能带理论、性质,及光子晶体和半导体的区别和联系。     

镜像对称的光子晶体透射带特性

通过传输矩阵方法计算了镜像对称光子晶体的带隙结构,结果表明该结构具有优越的窄带滤波性能.如果在该光子晶体两端均加入较高的折射率介质,构成夹心"三明治"结构,这时的光子晶体透射带结构出现多通道滤波特性;当两端加入不同的较高折射率介质但其光学厚度仍保持为基本结构单元的光学厚度时,得到宽度为50~2500 nm大范围的低透射区,其具有宽带阻波作用;当两端加入的不同高折射率介质但光学厚度变为基本光学厚度的两倍时,则得到在中心波长处出现非常窄的完全透射峰,这种带隙结构可用来设计优异理想窄带滤波器.     

Three-dimensional control of light in a two-dimensional photonic crystal slab

Optoelectronic devices are increasingly important in communication and information technology. To achieve the necessary manipulation of light (which carries information in optoelectronic devices), considerable efforts are directed at the development of photonic crystals--periodic dielectric materials that have so-called photonic bandgaps, which prohibit the propagation of photons having energies within the bandgap region. Straightforward application of the bandgap concept is generally thought to require three-dimensional (3D) photonic crystals; their two-dimensional (2D) counterparts confine light in the crystal plane, but not in the perpendicular z direction, which inevitably leads to diffraction losses. Nonetheless, 2D photonic crystals still attract interest because they are potentially more amenable to fabrication by existing techniques and diffraction losses need not seriously impair utility. Here we report the fabrication of a waveguide-coupled photonic crystal slab (essentially a free-standing 2D photonic crystal) with a strong 2D bandgap at wavelengths of about 1.5 microm, yet which is capable of fully controlling light in all three dimensions. These features confirm theoretical calculations on the possibility of achieving 3D light control using 2D bandgaps, with index guiding providing control in the third dimension, and raise the prospect of being able to realize unusual photonic-crystal devices, such as thresholdless lasers.     

Novel 1-D Sandwich Photonic Bandgap Structure

A sandwich photonic bandgap (PBG) structure is a novel PBG structure whose periodic lattice is buried in the middle of a substrate. Neither drilling nor suspending the substrate is required, and the integrity of the ground plane is maintained. This paper presents several modification techniques for sandwich PBG structure fabrication. The forbidden gap can be improved by adopting the chirping technique, applying the tapering technique, enlarging the periodic elements, adjusting the location of the periodic lattice in the substrate, and using different dielectric media H-shape elements. A finite difference time domain method is applied to analyze the structures. Deep and wide stopbands can be obtained using the modified sandwich structures. Experimental measurement results agree well with the theoretical analysis.     

SiO2/ZnO 三维光子晶体的制备及光学性质

采用垂直沉积法制备了三维SiO2光子晶体模板。以醋酸锌为前躯体,成功制备了SiO2/ZnO三维复合光子晶体。扫描电子显微镜测试结果表明SiO2和SiO2/ZnO光子晶体均为面心立方结构排列。光学测试表明SiO2和SiO2/ZnO周期性阵列均在[111]方向出现了光子带隙。当具有较高折射率的ZnO材料包覆后,SiO2/ZnO 光子晶体[111]方向光子带隙的中心波长发生红移,光子晶体基元材料的有效折射率有所增加。同时,光子晶体的光学性质与样品内部的缺陷态密度密切相关。