One-dimensional photonic crystal design

In this article we present a method to determine the band spectrum, band gaps, and discrete energy levels, of a one-dimensional photonic crystal with localized impurities. For one-dimensional crystals with piecewise constant refractive indices we develop an algorithm to recover the refractive index distribution from the period map. Finally, we derive the relationship between the period map and the scattering matrix containing the information on the localized modes.     

Improved design of polarization-maintaining photonic crystal fibers

We propose the realization of single-polarization operation in highly birefringent photonic crystal fibers. The suppression of one of the polarization states is realized by introducing index-matched cladding defect waveguides. The leakage loss of the index-matched polarization state can be enhanced by nearly 4 orders of magnitude. In particular, polarization-dependent loss larger than 2.97 dB/m with transmission loss lower than 0.03 dB/m in a wavelength region ranging from 1.54 to 1.566 microm can be realized in one such fiber.     

A geometry optimization framework for photonic crystal design

The performance of photonic crystal devices can depend strongly on their geometry. Alas, their fundamental physics offers relatively little by way of pointers in terms of optimum shapes, so numerical design search techniques must be used in an attempt to determine high performance layouts. We discuss strategies for solving this type of optimization problem, the main challenge of which is the conflict between the enormous size of the space of potentially useful designs and the relatively high computational cost of evaluating the performance of putative shapes. The optimization technique proposed here operates over increasing levels of fidelity, both in terms of the resolution of its non-parametric shape definition and in terms of the resolution of the numerical analysis of the performance of putative designs. This is a generic method, potentially applicable to any type of electromagnetic device shape design problem. We also consider a methodology for assessing the robustness of the optima generated through this process, investigating the impact of manufacturing errors on their performance. As an illustration, we apply this technology to the design of a two-dimensional photonic crystal structure; the result features a large complete band gap structure and a topology that is different from previously published designs.     

光子晶体偏振分光镜的优化设计

提出了一种二维光子晶体偏振分光镜的设计方法,介绍了光栅基板上用Ge/BaF₂ 多层膜实现二维光子晶体偏振分光镜的优化设计.结果表明，TE模式的光子禁带宽度为0083(2πc/a, a是光栅的周期),设计的偏振波长从172μm到24μm，相对带宽为331％.此光子晶体偏振器件制作简单,具有实用性. 关键词： 偏振分光镜 光子晶体 光子禁带     

Highly birefringent and dichroic photonic crystal VCSEL design

We analyse the possibility to stabilise the polarisation of light emitted by photonic crystal vertical-cavity surface-emitting lasers (PC-VCSELs). We consider two different photonic crystal configurations in a GaAs/AlGaAs VCSEL: with elliptical holes and with selectively enlarged holes and a small central hole. Very large birefringence (∼400 GHz) and dichroism (∼7%) are demonstrated for the second PC-VCSEL design.     

Modified design of photonic crystal fibers with flattened dispersion

We present a modified method to design photonic crystal fibers with flattened dispersion characteristics. By replacing the circular air-holes of the first central ring with elliptic air-holes, we observe a more flattened dispersion curve. Plane-wave expansion (PWE) method is used to analyze the dispersion property in a high-index core PCF. The simulation results are presented, and ultra-low and ultra-flattened dispersion curves over wide wavelength range are demonstrated.     

Semi-analytic method for slow light photonic crystal waveguide design

We present a semi-analytic method to calculate the dispersion curves and the group velocity of photonic crystal waveguide modes in two-dimensional geometries. We model the waveguide as a homogenous strip, surrounded by photonic crystal acting as diffracting mirrors. Following conventional guided-wave optics, the properties of the photonic crystal waveguide may be calculated from the phase upon propagation over the strip and the phase upon reflection. The cases of interest require a theory including the specular order and one other diffracted reflected order. The computational advantages let us scan a large parameter space, allowing us to find novel types of solutions.     

一种基于光子晶体结构的坦克涂层设计

为减少坦克在实战中的红外辐射, 分析了坦克炮慢射后的辐射特征, 针对其炮管所辐射的特征波长在8-12 μm的电磁波,选用常见的SiO₂和Si为介质, 并在考虑各自色散关系的基础上, 设计了具有光子晶体结构的防辐射涂层. 数值计算表明: 当两介质各取4层, 其几何厚度分别取1330和825 nm时,在8-12 μm 的范围内有一个严格的带隙. 当两介质的几何厚度增加, 带隙红移, 宽度增加, 反之亦然. 只要两介质的几何厚度变化不同时超过10%, 原带隙总是存在. 当介质层数取7-8时, 涂层在上述波长范围内的严格带隙已形成, 介质层数再增加, 带隙没有实质性的变化. 带隙结构对入射角的变化并不敏感.     

Silica-air photonic crystal fiber design that permits waveguiding by a true photonic bandgap effect

A theoretical investigation of a novel type of optical fiber is presented. The operation of the fiber relies entirely on wave guidance through the photonic bandgap effect and not on total internal reflection, thereby distinguishing that fiber from all other known fibers, including recently studied photonic crystal fibers. The novel fiber has a central low-index core region and a cladding consisting of a silica background material with air holes situated within a honeycomb lattice structure. We show the existence of photonic bandgaps for the silica-air cladding structure and demonstrate how light can be guided at the central low-index core region for a well-defined frequency that falls inside the photonic bandgap region of the cladding structure.     

多层对称薄膜的光子晶体光波导设计

基于多层对称薄膜的反射镜作用,设计了一种工作波长位于1550nm附近的基于周期性多层膜的光子晶体光波导。由平板波导的相关理论分析了波长在1515~1587nm范围内电磁波在波导中的传输性质。研究表明TE模和TM模在波导都是基模传输,其功率约束因子(Γ)限制在0.99~1之间,说明波导近乎完全将光波限制在其中传输。在控光能力上这种结构要比普通的三层薄膜波导更具优势。利用周期性多层膜的光子带隙结构,可以构造具有超低损耗的全向带隙介质光波导。     

Light source design using Kagome-lattice hollow core photonic crystal fibers

Supercontinuum (SC) light source is designed using high pressure Xe-filled hollow core Kagome-lattice photonic crystal fiber. Using finite element method with perfectly matched layer, SC spectra in normal chromatic dispersion region have been generated using picosecond optical pulses from relatively less expensive laser sources.     

Parallel microgenetic algorithm design for photonic crystal and waveguide structures

We have developed a powerful parallel genetic algorithm design tool for photonic crystal and waveguide structures. The tool employs a small-population-size genetic algorithm (microgenetic algorithm) for global optimization and a two-dimensional finite-difference time-domain method to rigorously design and optimize the performance of photonic devices. We discuss the implementation and performance of this design tool. We demonstrate its application to two photonic devices, a defect taper coupler to connect conventional waveguides and photonic crystal waveguides, and a sharp 90 degrees waveguide bend for low index contrast waveguides.     

Analysis and design of efficient coupling in photonic crystal circuits

A rigorous analysis and design of efficient coupling from photonic crystal (PhC) waveguides into conventional dielectric waveguides is reported. Closed-form expressions for the reflection and transmission matrices that completely characterize the scattering that occurs at the interface are derived based on an eigenmode expansion technique and a Bloch basis. Analytic expressions are used to analyze the reflection into PhC waveguides. We obtain that negligible reflection can be achieved by choosing a certain interface within a PhC unit cell. Furthermore, analytic expressions are used to design a novel and compact coupler structure in order to achieve high coupling efficiency when broad dielectric waveguides are considered. Thereby, transmission efficiencies near 100 from the fundamental guided Bloch mode into the fundamental waveguide mode are achieved.     

Dirac光子晶体

Dirac费米子作为粒子物理中的基本粒子之一,其理论在近年来蓬勃发展的拓扑电子理论领域中被广泛提及并用来刻画具有Dirac费米子性质的电子态.这种特殊的能态通常被称为Dirac点,在能谱上表现为两条不同能带之间的线性交叉点.由于Dirac点往往是发生拓扑相变的转变点,因而也被视为实现各种拓扑态的重要母态.作为可与拓扑电子体系类比的拓扑光子晶体因其独特的潜在应用价值也受到人们的广泛关注,实现包含Dirac点的光子能带已成为研究拓扑光子晶体的核心课题.本文基于电子的拓扑理论,简要地回顾了Dirac点在光子系统中的研究进展,特别介绍了如何在光子晶体中利用不同晶格对称性实现在高对称点/线上的Dirac点,以及由Dirac点衍生的Weyl点.     

Improved air-silica photonic crystal with a triangular airhole arrangement for hollow-core photonic bandgap fiber design

We propose an improved photonic crystal (PC) cladding design for existing air-guiding photonic bandgap (PBG) fibers whose cladding airholes are arranged in a triangular lattice pattern. By increasing the sizes of concentrated silica regions in the cladding PC, we can have a larger degree of freedom in controlling the cladding bandgap regions. We predict that a fiber made from this type of cladding would perform better in terms of the PBG-guiding wavelength range, radiation loss owing to finite cladding size, and the ability to avoid surface mode problems.     

Graphene-based photonic crystal

A novel type of photonic crystal formed by embedding a periodic array of constituent stacks of alternating graphene and dielectric discs into a background dielectric medium is proposed. The photonic band structure and transmittance of such photonic crystal are calculated. The graphene-based photonic crystals can be used effectively as the frequency filters and waveguides for the far infrared region of electromagnetic spectrum. Due to substantial suppression of absorption of low-frequency radiation in doped graphene the damping and skin effect in the photonic crystal are also suppressed. The advantages of the graphene-based photonic crystal are discussed.     

光子晶体中的磁控光子开关线路

提出了一个光子晶体中的磁控光子开关线路的理论模型,并利用平面波展开加超原胞方法计算了它的光学性质.这个模型由设置在空气中的介电柱子光子晶体构成,其中一排柱子被具有同样介电常数的铁氧体柱子替换.当外加磁场时,铁氧体柱子产生了不等于一的磁导率,这就会在光子带隙中产生波导模.当撤去外场,整个体系还原为完美光子晶体.由此便可形成磁控光子开关线路.具体选择了正方形柱子设置在正方形格点上,计算结果证明这种设想是可行的,并给出一些有价值的结果. 关键词： 光子晶体 传导模 磁导率     

The design of a photonic crystal filter in the terahertz range

One-dimensional photonic crystal structures for multiple channeled filtering and polarization selective filtering in the terahertz (THz) range are studied theoretically. The design of aperiodic photonic quantum-well (APQW) structures for multiple channeled filtering and different polarization filtering at arbitrary preassigned frequencies are achieved by using the simulated annealing algorithm with a special merit function. The parameters of these filters can be expediently controlled and the transmission characters are polarization dependent. Numerical simulations show that the designed APQWs can meet the desired specification well.     

Localized photonic modes in photonic crystal heterostructures

In this work, interface modes of two-dimensional photonic crystal heterostructures have been investigated by usage of the supercell method. The photonic crystal heterostructure is made of two photonic crystals with square symmetry in which one of them is composed of circular dielectric rods in air background and the other one is constructed by drilled square holes in dielectric. It is shown that using of a proper supercell plays an important role in obtaining the correct interface modes. We have also showed that the guided interface modes and single mode which is different from those reported in some published works are nearly dispersionless.     

A novel design of a photonic crystal sensor with improved sensitivity

Biosensors, based on photonic crystal (PC), are emergent subject. The use of PCs in this area brought solutions to both miniaturization and integration challenges that have been facing research groups for long time. We are only recently, by engineering such defects, able to propagate light in complex structures containing molecules of different sizes and shapes. We propose a novel structure containing defects with various sizes. The PC is formed by a dielectric cylinders with permittivity 8.9 (alumina Al₂O₃) and a radius r = 0.2a (a is the square lattice constant), arranged in a square lattice. We use the finite difference time domain to investigate the sensitivity of the proposed sensor to water. The defect based sensing element is introduced in two directions 〈0 1〉 and 〈1 0〉. These simulations show a better sensitivity to water than other analytes. It appears in the transmission curves where the peak shifts to high frequency when the refractive index is changed.