基于二维六方氮化硼材料的光子晶体非对称传输异质结构设计

二维六方氮化硼(hexagonal boron nitride,hBN)材料在产生光学稳定的超亮量子单光子光源领域有着潜在应用,有望用于量子计算和信息处理平台,已成为研究热点.而光学非对称传输设备是集成量子计算芯片中的关键器件之一.本文从理论上提出了一种基于hBN材料光子晶体异质结构的纳米光子学非对称光传输器件.运用平...     

Optics design and fabrication of 3D electrically switchable hexagonal photonic crystal

We demonstrate a holographic approach for easy and large-area fabrication of 3D photonic crystal (PhC) microstructures in a polymer-dispersed liquid crystal (PDLC) by applying a single top-cut hexagonal prism and a seven-beam interference system. Based on the expected photonic band gap of the photonic crystal, the prism parameters are designed and optimized. For example, a prism with a height h=3.73 cm and a cross angle α=66° between the side face and the base is used to fabricate 3D PhC hexagonal symmetrical structures in PDLCs. A good agreement is obtained between the theoretical calculation of the interference intensity and morphological structures. On the other hand, far-field diffraction patterns and electrical switching characteristics are also investigated. PACS 42.15.Eq; 42.40.Eq     

2D and 3D electrically switchable hexagonal photonic crystal in the ultraviolet range

Two holographic lithography systems are demonstrated for easy and large-area fabrication of 2D and 3D photonic crystal (PhC) microstructures in a polymer dispersed liquid crystal (PDLC) by applying a single top-cut hexagon prism. A six-beam system has been used to produce 2D hexagonal PhCs. By adding an additional mirror, a twelve-beam system is demonstrated to fabricate 3D PhCs with ultraviolet (UV) band-gap along the z direction. A good agreement is obtained for measured PhCs structure and theoretical results. Far-field diffraction patterns and electrical switching characteristics of the 2D and 3D PhC HPDLC films have been investigated. PACS 42.15.Eq; 42.40.Eq     

FDTD analysis of 2D triangular-lattice photonic crystals with arbitrary-shape inclusions based on unit cell transformation

A finite-difference time-domain method based on Yee’s orthogonal cell is utilized to calculate the band structures of 2D triangular-lattice-based photonic crystals through a simple modification to properly shifting the boundaries of the original unit cell. A strategy is proposed for transforming the triangular unit cell into an orthogonal one, which can be used to calculate the band structures of 2D PhCs with various shapes of inclusions, such as triangular, quadrangular, and hexagonal shapes, to overcome the shortage of plane-wave expansion method for circular one. The band structures of 2D triangular-lattice-based PhCs with hexagonal air-holes are calculated and discussed for different values of its radius and rotation angle. The obtained results provide an insight to manipulate the band structures of PhCs.     

Demonstration of temperature resilient properties of 2D silicon carbide photonic crystal structures and cavity modes

In this paper, photonic crystal (PhC) based on two dimensional (2D) square and hexagonal lattice periodic arrays of Silicon Carbide (SiC) rods in air structure have been investigated using plane wave expansion (PWE) method. The PhC designs have been optimized for telecommunication wavelength (λ = 1.55 μm) by varying the radius of the rods and lattice constant. The result obtained shows that a photonic band gap (PBG) exists for TE-mode propagation. First, the effect of temperature on the width of the photonic band gap in the 2D SiC PhC structure has been investigated and compared with Silicon (Si) PhC. Further, a cavity has been created in the proposed SiC PhC and carried out temperature resiliency study of the defect modes. The dispersion relation for the TE mode of a point defect A1 cavity for both SiC and Si PhC has been plotted. Quality factor (Q) for both these structures have been calculated using finite difference time domain (FDTD) method and found a maximum Q value of 224 for SiC and 213 for Si PhC cavity structures. These analyses are important for fabricating novel PhC cavity designs that may find application in temperature resilient devices.     

由球形原子构成的多种周期性介电结构的光子能带计算

采用矢量平面波方法计算了由球形空气原子构成的体心立方结构和六角密堆结构的光子能带，两种结构下都看到了贯通整个布里渊区的禁带。本文预言周期性介电结构的最大折射率调制度和最大禁带宽度对应于同样的原子体积分数，而且这个最佳的原子体积分数是结构无关的。文中还计算了由各向异性介电小球构成的面心立方结构的光子能带并看到了禁带，这与各向同性介电小球构成的面心立方结构很不相同。     

A novel proposal for enhancement of light extraction efficiency in WOLEDs based on optimized photonic crystal structures

In this paper we propose a framework to enhance light extraction efficiency in white organic light emitting diodes (WOLED) using photonic crystal (PhC) structures sandwiched between indium tin oxide (ITO, n_ITO = 1.8+0.01i) and glass (n_glass = 1.51) substrate, according to the high refractive index contrast of these two layers almost 50% of the generated light inside WOLED gets trapped in the mentioned interface. The main purpose of this article is to suggest a method to intentionally optimize PhC structures to reduce total internal reflections (TIR) happening at ITO/glass interface. Here three different patterns are considered including rectangular, hexagonal and circular lattices. Using Finite Difference Time Domain (FDTD) method and the presented framework for choosing structural parameters the portion of 50% trapped light in ITO was reduced to 20% which is a large enhancement in extraction efficiency of WOLED. Also far-field results before and after adding PhCs are investigated.     

Broadening of band-gap in photonic crystals with optically saturated media

Due to strong absorption of the incident light, the media with high refractive index are considered restrictive for applications in photonic crystals (PhCs). The possibility to resolve this problem by optical saturation effectively minimizing the absorption of the PhC medium is discussed. Such approach might be promising for the significant broadening of the photonic band-gap.     

含负磁导率或双负材料的一维光子晶体的全方位带隙中波的反射相位特性

运用传输矩阵法研究了含负磁导率或双负材料的一维光子晶体结构在全方位光子禁带中波的反射相位谱.研究发现"负磁导率材料-正折射率材料"光子晶体和"双负材料-正折射率材料"光子晶体,在所述带隙中,对TE波而言,反射相位随入射角的增大而增大;对TM波而言,禁带频率范围内波的反射相位随入射角的增大而减小;TE波和TM波,两种结构的反射位相均随介质层的厚度缩放因子增大而增大,且都与周期数无关.     

Enhancement of the light output of light-emitting diode with double photonic crystals

A light-emitting diode (LED) with double photonic crystals (PhCs) is designed to enhance the light output. Based on the configuration of the PhC assisted LED with a single PhC (SPC-LED), a second PhC is added on the bottom surface of the active layer to improve the light output. The optical properties of this double PhCs assisted LED are simulated using the three-dimensional (3D) finite-difference time-domain (FDTD) method. The calculation results show that its light output can be 3.2 times higher than that of LED without PhC, and 1.39 times higher than that of SPC-LED.     

High Efficiency One-Way Transmission by One-Dimensional Photonic Crystals with Gratings on One Side

We propose a scheme of optical one-way transmission by using one-dimensional photonic crystals （PhCs） with diffraction gratings on one side. The one-way transmission is realized by making the PhC opaque to the zeroth diffraction order and transparent to another propagating （in air） diffraction order. For such a structure with 10-period PhC, 93% of the incident energy passes through when an electromagnetic wave impinges from one side, and the transmittance decreases to the order of 0.001% as the electromagnetic wave illuminates from the other side.     

蛋白石型光子晶体红外隐身材料的制备

基于光子晶体的红外隐身材料,主要采取一维层层堆叠结构和三维木堆结构等来实现对红外波段电磁波辐射性能的调控.本文报道了一种操作简易、成本低廉的光子晶体红外隐身材料制备方法.通过优化的垂直沉积法,微米级SiO_2胶体微球自组装成高质量的蛋白石型光子晶体结构.对SiO_2胶体微球进行优选,成功制备了禁带位于2.8—3.5μm,8.0—10.0μm的SiO_2胶体晶体蛋白石型光子晶体材料.该材料可改变目标相应波段的红外辐射特征,具有目标红外波段的隐身效果.     

有限开敞介质光子晶体的模式及其带结构分析

针对光子晶体在行波管中的应用,对有限开敞介质光子晶体的模式和带结构进行了分析和计算. 分析表明,有限开敞介质光子晶体中所能存在的模式包括EH和HE混合模式,如果是二维光子晶体,还存在E模式,E₁模式即为无限光子晶体中的E极化. 计算表明,被用作行波管慢波电路的光子晶体可以不必拥有完全带隙,而只需要具有带间隙即可. 关键词： 光子晶体 本征值方程 行波管 带结构     

Non-Bragg band gaps and light manipulation of composite structures with metamaterials

A review is presented of various composite structures containing double-negative metamaterials or two types of single-negative metamaterials. In particular, non-Bragg band gaps arising from phase-compensation or tunneling effects and their manipulation of light are stressed. The non-Bragg band gaps that are robust against incident directions, thickness randomness and are easily tuned by changing the structural parameters can not only expand our ability in controlling the flow of light, but also provide new mechanisms for the design of photonic devices.     

Dispersion-based beam splitter in photonic crystals

A novel implementation of a dispersion-based beam splitter in a photonic crystal (PhC) is proposed. The beam splitter consists of two periodic structures: a nonchannel dispersion-guiding region and a splitting structure operating inside the photonic bandgap. The dispersion-guiding PhC structure is used to route the optical wave by exploiting the dispersion properties of the lattice. An arbitrary power ratio between the output beams can be achieved by varying the parameters of the splitting structure. Within the studied range of splitting structures, high output power was observed and verified experimentally.     

Polarization characteristics of chiral photonic crystal fibers with an elliptical hollow core

The theoretical study of dielectric-chiral photonic crystal fiber(PCF)with an elliptical hollow core is presented.The band structure of chiral photonic crystal(PhC)is calculated by using a modified plane-wave expansion(PWE)method.By examining the out-of-plane photonic bandgaps(PBGs)of chiral PhC,a kind of chiral PCF with a hollow core is designed and their eigenstates are calculated.The distributions of mode field and polarization state are demonstrated,and how the structural asymmetry of the core together with the chirality in the background affects the modal polarization is discussed.The dependences of birefringence on chirality for different ellipticities of core are investigated.     

Holographic design of hexagonal photonic crystals of irregular columns with large full band gap

The shape and size of the dielectric columns or particles (“atoms”) of photonic crystals (PhCs) formed by holographic lithography are determined by the isointensity surfaces of the interference field; consequently the PhCs’ photonic band gap (PBG) properties are closely related to their fabrication design. Here we have proposed a new structure of two-dimensional (2-D) hexagonal lattice with irregular columns, which can yield a 2-D complete relative band gap of 24.0% in case of the dielectric columns of ε = 13.6 in air, about 27% increase compared with that of the same lattice with regular triangular columns. This band gap size is among the largest for all the possible 2-D PhCs reported until now. The relationship between band gap properties of resultant structure and the specific fabrication conditions such as structure design and the choice of optimum intensity threshold and filling ratio are systematically discussed. The optical design for making this structure by two exposures is explained. This work may demonstrate the unique feature and advantages of photonic crystals made by holographic method and provide a guideline for their design and experimental fabrication.     

Square lattice photonic-crystal collimator

The anomalous dispersion of planar photonic crystals (PhCs) near the dielectric band edge is utilised to control the wavelength-dependent propagation of light. Light beams with up to ±10° divergence were cleanly collimated over a 40 nm (1260–1300 nm) bandwidth using a square lattice. The collimating range and angular dispersion sensitivity between the square and hexagonal lattice have been compared. Both the plane-wave expansion calculation and finite difference time domain (FDTD) simulation match well with the experimental results.     

GaN-based LEDs surrounded with a two-dimensional nanohole photonic crystal structure for effective laterally guided mode coupling

Traditional implementation of photonic crystals (PhCs) on LED light emission surfaces results in weak coupling of light with the PhCs. Here we introduce a GaN-based LED surrounded with a nanohole PhC structure along the mesa edges. The laterally guided modes in the epi-structure can be effectively coupled with the two-dimensional periodic structure. The proposed structure results in the improvement of LED light extraction and provides flexibility of radiation directionality control.     

Design and optimization of one-dimensional photonic crystals for thermophotovoltaic applications

We explore the optical characteristics and fundamental limitations of one-dimensional (1D) photonic crystal (PhC) structures as means for improving the efficiency and power density of thermophotovoltaic (TPV) and microthermophotovoltaic (MTPV) devices. We analyze the optical performance of 1D PhCs with respect to photovoltaic diode efficiency and power density. Furthermore, we present an optimized dielectric stack design that exhibits a significantly wider stop band and yields better TPV system efficiency than a simple quarter-wave stack. The analysis is done for both TPV and MTPV devices by use of a unified modeling framework.