二维六边形晶格光子晶体的带隙研究

运用平面波展开法模拟计算了二维六边形晶格光子晶体的能带结构,得到了使光子带隙最大化的结构参数.分别以不同介质作为本底,由圆柱、正方直柱和六角形直柱空气孔构成的六边形晶格光子晶体都出现了完全光子带隙,为进一步光子晶体的实验制备和应用提供了理论依据.     

二维函数光子晶体不同函数形式对带隙结构的调控

用平面波展开法研究二维函数光子晶体介质柱介电常数不同的线性函数形式对横电(TE)波和横磁(TM)波带结构的影响. 数值计算结果表明: 二维函数光子晶体比二维常规光子晶体的带隙更宽; 通过变换介质柱介电常数不同的线性函数形式可使二维函数光子晶体的带隙个数、位置和宽度均发生变化, 从而实现对二维函数光子晶体带隙的调节.     

All-metallic three-dimensional photonic crystals with a large infrared bandgap

Three-dimensional (3D) metallic crystals are promising photonic bandgap structures: they can possess a large bandgap, new electromagnetic phenomena can be explored, and high-temperature (above 1,000 degrees C) applications may be possible. However, investigation of their photonic bandgap properties is challenging, especially in the infrared and visible spectrum, as metals are dispersive and absorbing in these regions. Studies of metallic photonic crystals have therefore mainly concentrated on microwave and millimetre wavelengths. Difficulties in fabricating 3D metallic crystals present another challenge, although emerging techniques such as self-assembly may help to resolve these problems. Here we report measurements and simulations of a 3D tungsten crystal that has a large photonic bandgap at infrared wavelengths (from about 8 to 20 microm). A very strong attenuation exists in the bandgap, approximately 30 dB per unit cell at 12 microm. These structures also possess other interesting optical properties; a sharp absorption peak is present at the photonic band edge, and a surprisingly large transmission is observed in the allowed band, below 6 microm. We propose that these 3D metallic photonic crystals can be used to integrate various photonic transport phenomena, allowing applications in thermophotovoltaics and blackbody emission.     

有旋转六角洞的光子晶体的最大绝对带隙和缺陷模

研究有旋转六角洞的三角点阵二维光子晶体的带结构,探索单元核几何对称性减少对绝对带隙值和局域缺陷模频率值的影响。对洞的中等旋转角,我们揭示此结构的最大绝对带隙可以获得,且该角依赖于洞的半径和背景材料的折射指数。我们也研究了由洞的缺失产生的缺陷模的特点,讨论了此结构模的可调性。     

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.     

Supramolecular dendritic liquid quasicrystals

A large number of synthetic and natural compounds self-organize into bulk phases exhibiting periodicities on the 10(-8)-10(-6) metre scale as a consequence of their molecular shape, degree of amphiphilic character and, often, the presence of additional non-covalent interactions. Such phases are found in lyotropic systems (for example, lipid-water, soap-water), in a range of block copolymers and in thermotropic (solvent-free) liquid crystals. The resulting periodicity can be one-dimensional (lamellar phases), two-dimensional (columnar phases) or three dimensional ('micellar' or 'bicontinuous' phases). All such two- and three-dimensional structures identified to date obey the rules of crystallography and their symmetry can be described, respectively, by one of the 17 plane groups or 230 space groups. The 'micellar' phases have crystallographic counterparts in transition-metal alloys, where just one metal atom is equivalent to a 10(3)-10(4)-atom micelle. However, some metal alloys are known to defy the rules of crystallography and form so-called quasicrystals, which have rotational symmetry other than the allowed two-, three-, four- or six-fold symmetry. Here we show that such quasiperiodic structures can also exist in the scaled-up micellar phases, representing a new mode of organization in soft matter.     

Dodecagonal tiling in mesoporous silica

Recent advances in the fabrication of quasicrystals in soft matter systems have increased the length scales for quasicrystals into the mesoscale range (20 to 500 ?ngstr?ms). Thus far, dendritic liquid crystals, ABC-star polymers, colloids and inorganic nanoparticles have been reported to yield quasicrystals. These quasicrystals offer larger length scales than intermetallic quasicrystals (a few ?ngstr?ms), thus potentially leading to optical applications through the realization of a complete photonic bandgap induced via multiple scattering of light waves in virtually all directions. However, the materials remain far from structurally ideal, in contrast to their intermetallic counterparts, and fine control over the structure through a self-organization process has yet to be attained. Here we use the well-established self-assembly of surfactant micelles to produce a new class of mesoporous silicas, which exhibit 12-fold (dodecagonal) symmetry in both electron diffraction and morphology. Each particle reveals, in the 12-fold cross-section, an analogue of dodecagonal quasicrystals in the centre surrounded by 12 fans of crystalline domains in the peripheral part. The quasicrystallinity has been verified by selected-area electron diffraction and quantitative phason strain analyses on transmission electron microscope images obtained from the central region. We argue that the structure forms through a non-equilibrium growth process, wherein the competition between different micellar configurations has a central role in tuning the structure. A simple theoretical model successfully reproduces the observed features and thus establishes a link between the formation process and the resulting structure.     

Complete photonic bandgaps in 12-fold symmetric quasicrystals

Photonic crystals are attracting current interest for a variety of reasons, such as their ability to inhibit the spontaneous emission of light. This and related properties arise from the formation of photonic bandgaps, whereby multiple scattering of photons by lattices of periodically varying refractive indices acts to prevent the propagation of electromagnetic waves having certain wavelengths. One route to forming photonic crystals is to etch two-dimensional periodic lattices of vertical air holes into dielectric slab waveguides. Such structures can show complete photonic bandgaps, but only for large-diameter air holes in materials of high refractive index (such as gallium arsenide, n = 3.69), which unfortunately leads to significantly reduced optical transmission when combined with optical fibres of low refractive index. It has been suggested that quasicrystalline (rather than periodic) lattices can also possess photonic bandgaps. Here we demonstrate this concept experimentally and show that it enables complete photonic bandgaps--non-directional and for any polarization--to be realized with small air holes in silicon nitride (n = 2.02), and even glass (n = 1.45). These properties make photonic quasicrystals promising for application in a range of optical devices.     

On-chip natural assembly of silicon photonic bandgap crystals.

Photonic bandgap crystals can reflect light for any direction of propagation in specific wavelength ranges. This property, which can be used to confine, manipulate and guide photons, should allow the creation of all-optical integrated circuits. To achieve this goal, conventional semiconductor nanofabrication techniques have been adapted to make photonic crystals. A potentially simpler and cheaper approach for creating three-dimensional periodic structures is the natural assembly of colloidal microspheres. However, this approach yields irregular, polycrystalline photonic crystals that are difficult to incorporate into a device. More importantly, it leads to many structural defects that can destroy the photonic bandgap. Here we show that by assembling a thin layer of colloidal spheres on a silicon substrate, we can obtain planar, single-crystalline silicon photonic crystals that have defect densities sufficiently low that the bandgap survives. As expected from theory, we observe unity reflectance in two crystalline directions of our photonic crystals around a wavelength of 1.3 micrometres. We also show that additional fabrication steps, intentional doping and patterning, can be performed, so demonstrating the potential for specific device applications.     

材料色散对一维光子晶体带隙的影响研究

运用传输矩阵方法研究了材料色散对传统周期结构一维光子晶体光子带隙的影响.计算结果表明,考虑色散后,光子带隙既可能变窄也可能增宽,既可能发生红移也可能发生蓝移.光子带隙的改变与色散材料的色散强度、谐振频率及2介质材料折射率差的改变相关.色散强度越大对光子带隙的影响也越大.一般来说,若考虑色散后两介质材料的折射率差增大,则...     

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。     

用转移矩阵方法计算一维光子晶体的禁带结构

该文提出了一种利用转移矩阵来计算一维光子晶体的光子禁带结构的新方法．利用此方法计算了不同介电常量、不同几何结构的晶体的禁带特征，并讨论了掺杂后的一维光子晶体光子禁带的变化情况．     

Wave and defect dynamics in nonlinear photonic quasicrystals

Quasicrystals are unique structures with long-range order but no periodicity. Their properties have intrigued scientists ever since their discovery and initial theoretical analysis. The lack of periodicity excludes the possibility of describing quasicrystal structures with well-established analytical tools, including common notions like Brillouin zones and Bloch's theorem. New and unique features such as fractal-like band structures and 'phason' degrees of freedom are introduced. In general, it is very difficult to directly observe the evolution of electronic waves in solid-state atomic quasicrystals, or the dynamics of the structure itself. Here we use optical induction to create two-dimensional photonic quasicrystals, whose macroscopic nature allows us to explore wave transport phenomena. We demonstrate that light launched at different quasicrystal sites travels through the lattice in a way equivalent to quantum tunnelling of electrons in a quasiperiodic potential. At high intensity, lattice solitons are formed. Finally, we directly observe dislocation dynamics when crystal sites are allowed to interact with each other. Our experimental results apply not only to photonics, but also to other quasiperiodic systems such as matter waves in quasiperiodic traps, generic pattern-forming systems as in parametrically excited surface waves, liquid quasicrystals, and the more familiar atomic quasicrystals.     

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.     

二维光子晶体绝对带隙的研究

晶体中获得大的绝对带隙，可以通过降低格子对称性解除简并来实现。格子对称性的降低一般可以通过向晶体的原胞内引入不同半径的柱子的方法实现，在该方法基础上结合滑移操作，对二维正方形光子晶体结构进行了研究，发现这种联合方法用于打开绝对带隙特别有用，其相对带隙宽度约为“双柱子正方形格子”情况的2倍，同时还使绝对带隙出现的位置向低频处移动。     

三角形结构复合二维光子晶体的透射谱

选择3种不同介质柱半径的光子晶体构造复合二维光子晶体,采用时域有限差分方法（FDTD）,计算3种二维光子晶体和复合二维光子晶体的透射谱．结果表明：复合二维光子晶体的禁带宽度近似等于3种光子晶体带隙的叠加结果,结果还表明,随着介质柱半径的增大,光子晶体的带隙向长波方向移动．     

Fabrication of photonic crystals for the visible spectrum by holographic lithography

The term 'photonics' describes a technology whereby data transmission and processing occurs largely or entirely by means of photons. Photonic crystals are microstructured materials in which the dielectric constant is periodically modulated on a length scale comparable to the desired wavelength of operation. Multiple interference between waves scattered from each unit cell of the structure may open a 'photonic bandgap'--a range of frequencies, analogous to the electronic bandgap of a semiconductor, within which no propagating electromagnetic modes exist. Numerous device principles that exploit this property have been identified. Considerable progress has now been made in constructing two-dimensional structures using conventional lithography, but the fabrication of three-dimensional photonic crystal structures for the visible spectrum remains a considerable challenge. Here we describe a technique--three-dimensional holographic lithography--that is well suited to the production of three-dimensional structures with sub-micrometre periodicity. With this technique we have made microperiodic polymeric structures, and we have used these as templates to create complementary structures with higher refractive-index contrast.     

分析TE模式入射角对光子晶体禁带特性的影响

利用光学传输矩阵方法,分析了TE模式光波的入射角度分别与禁带宽度、光子带隙起始波长的关系,通过优化计算得到了一系列特殊带隙结构的光子晶体,揭示了光子晶体的带隙变化规律,对不同禁带范围的要求选取恰当参数来制备所需要的光子晶体提供了理论依据。     

Archimedean-like tiling on decagonal quasicrystalline surfaces

Monolayers on crystalline surfaces often form complex structures with physical and chemical properties that differ strongly from those of their bulk phases. Such hetero-epitactic overlayers are currently used in nanotechnology and understanding their growth mechanism is important for the development of new materials and devices. In comparison with crystals, quasicrystalline surfaces exhibit much larger structural and chemical complexity leading, for example, to unusual frictional, catalytical or optical properties. Deposition of thin films on such substrates can lead to structures that may have typical quasicrystalline properties. Recent experiments have indeed showed 5-fold symmetries in the diffraction pattern of metallic layers adsorbed on quasicrystals. Here we report a real-space investigation of the phase behaviour of a colloidal monolayer interacting with a quasicrystalline decagonal substrate created by interfering five laser beams. We find a pseudomorphic phase that shows both crystalline and quasicrystalline structural properties. It can be described by an archimedean-like tiling consisting of alternating rows of square and triangular tiles. The calculated diffraction pattern of this phase is in agreement with recent observations of copper adsorbed on icosahedral Al(70)Pd(21)Mn(9) surfaces. In addition to establishing a link between archimedean tilings and quasicrystals, our experiments allow us to investigate in real space how single-element monolayers can form commensurate structures on quasicrystalline surfaces.     

Photonic Bandgap Properties of One-Dimensional Photonic Crystal Consisting of Complex Artificial Media

0Introduction Photonicbandgap(PBG)structureshavebeenextensive lystudiedduringthepastdecade[13],duetothepossi bilityofhandlinglight.ThePBGmaterialsareperiodical structurescomposedofmetallicordielectricelements.Thefirstcharacteristicofthisbehavioristoforbidthepropagation oftheelectromagneticwaveswhosefrequencyincludedwithintheirfrequencybandgap.Thebanddependsonthematerial structure,i.e.,dimensions,periodicityandpermittivity.Thesecondmajorcharacteristicistheabilitytoopenlocalizedelec tromagnet…