Photonic crystals and microlasers fabricated with low refractive index material

Although the investigation on photonic band gap materials has been done more than two decades, it is still a big challenge to fabricate three-dimensional photonic crystal (PC) possessing wide band gaps in visible range. In this article, we have reviewed recent progresses on fabricating the PC with low refractive index material in visible range. In contrast to the material with large refractive index, it is cheap to use low refractive index material in fabricating the PC and will be greatly beneficial for future industrial productions. The holographic method to fabricate such a PC has been introduced, applying it to the design of the microlaser has also been discussed.     

Performance testing of log pile photonic crystal fast-fabricated by direct femtosecond laser writing

Great efforts has been made on fabricating photonic crystals （PCs） with photonic band gaps （PBGs） during the past decade. Three-dimensional （3D） log pile PC was fabricated fast by direct femtosecond laser writing in ORMOCER. Qualitative analysis of the errors of PC was investigated using the Image Pro Plus. Surface qualities such as bending, distortion, and surface roughness were shown, and the band gap in the infrared wavelength region was observed. Meanwhile, the theory was experimentally verified that the center of PBG diminishes as the crystal lattice period reduces. Therefore, it is possible to fabricate PCs whose band gap range is from the near-infrared to visible wave band.     

Demonstration of tunable complex refractive index of graphene covered one dimensional photonic crystals

Here, we report tunable complex optical properties of one dimensional photonic crystal covered by graphene layer, as a new optical material, in the visible spectral range. For this purpose, we fabricate two different structure as one dimensional photonic crystal, with photonic band gap which centered at 650 nm, by electron gun deposition method and the chemical vapor deposition has been used to synthesize graphene top layer. To demonstrate the optical properties of our two photonic crystals affected by graphene layer, we use the reflectance spectra of the samples as a function of incidence angle. Because the sufficient sensitivity of the refractive indices of the samples, we extract the real and imaginary part of these parameters in all of visible region as a tunable complex refractive index. Our results show that we have sufficient change due to excited plasmons in graphene layer by Bloch wave of photonic crystal which is very useful for sensor applications.     

非线性曝光对三维全息光子晶体禁带特性的影响

从理论和实验两方面研究了非线性曝光对全息方法制作光子晶体的影响.使用低折射率材料（n=152）制作了金刚石结构光子晶体,通过控制曝光量使记录介质工作在非线性曝光区域,发现光子禁带的特性得到了明显的改善.并由此提出了用低折射率材料实现全空间禁带的设想. 关键词： 光子晶体 光学全息 非线性曝光     

Analysis and optimization of a new photonic crystal filters in near ultraviolet band

Transmission characteristics of one-dimensional (1D) photonic crystals (PCs) heterostructures containing defective are studied using the transfer matrix method. The key is to search the best combination style for different 1D PCs to form heterostructures. It is shown that the non-transmission range over near ultraviolet and visible range can be substantially enlarged and the phenomenon of narrow band PC filter in near ultraviolet can be realized by adjusting the repeat cycle counts of various photonic crystals. The theoretical results on multiple heterostructures containing TiO₂/SiO₂ multilayer films are presented. With a perfect omni-directional and high peak transmission filters for TE modes, this structure opens a promising way to fabricate ultra-narrow band PC filters with wide non-transmission range in near ultraviolet and visible range.     

等效折射率为非-1时的亚波长成像

本文采用硅柱子周期性排列构成六角结构光子晶体,用平面波展开方法和FDTD方法研究表明,此结构光子晶体存在等效折射率接近-1的频率区域.在等效折射率趋于-1但不等于-1时,此光子晶体平板结构超透镜能形成一个非近场的像.模拟还发现,此结构平板光子晶体等效折射率为非-1时,可以亚波长成像. 关键词： 负折射 光子晶体 亚波长 成像     

高反射率硅基薄膜一维光子晶体的研究制备

采用射频等离子体增强化学气相沉积的方法,研究制备了一种基于硅基薄膜的高反射一维光子晶体。通过交替改变反应气体组分实现低折射率Si Ox层和高折射率a-Si层的交替层叠沉积,具有两种膜层介质折射率比大、反射率高、沉积时间短、工艺窗口宽等优点。采用5周期的Si Ox层与a-Si层构成的一维光子晶体(厚度分别为155 nm和55 nm),其禁带范围内(650~1 100 nm)的平均反射率达到99.1%,高于相同波长范围内Ag的平均反射率(96.3%)。     

Photonic band gap via quantum coherence in vortex lattices of Bose-Einstein condensates

We investigate the optical response of an atomic Bose-Einstein condensate with a vortex lattice. We find that it is possible for the vortex lattice to act as a photonic crystal and create photonic band gaps, by enhancing the refractive index of the condensate via a quantum coherent scheme. If high enough index contrast between the vortex core and the atomic sample is achieved, a photonic band gap arises depending on the healing length and the lattice spacing. A wide range of experimentally accessible parameters are examined and band gaps in the visible region of the electromagnetic spectrum are found. We also show how directional band gaps can be used to directly measure the rotation frequency of the condensate.     

光频段多频率域负折射率材料的数值研究

利用电介质材料周期性排列构成二维六角结构光子晶体,用平面波展开法研究了二维光子晶体材料各个能级的等频率曲线图,发现此结构光子晶体在多个频段上存在负折射特性,用时域有限差分(finite difference time domain,FDTD) 数值计算模拟也得到了相同的结果. 关键词： 光子晶体 左手化媒质 负折射 多频段     

介质柱型二维Triangular格子光子晶体的禁带特性

采用平面波展开法数值计算了空气背景中由圆形、正六边形和正方形介质柱构造的二维三角晶格光子晶体禁带结构,并研究了介质方柱旋转角度、介质折射率和填充比对完全光子禁带宽度的影响.结果表明,在低频区,介质方柱旋转17°时,出现最大完全光子禁带,且最大禁带宽度随介质折射率的变化较为稳定.在高频区,介质方柱旋转30°时,完全光子禁带宽度最大;且介质材料折射率n=2.2时即出现完全光子禁带,n=2.6时,完全光子禁带达到最大.     

光子晶体线缺陷波导中的折射率相位移调制增强效应

在传统的基于全内反射原理的低折射率比介质波导所构建的相位移调制型光学器件中,调制区域的长度通常在毫米到厘米量级.由于器件横向尺寸保持在微米量级,因此狭长结构成为了传统光波导器件的典型特征,这限制了光学器件集成度的提高,严重制约了集成光路的进一步发展.光子晶体的出现为高密集成光路的发展提供了一条新的途径.本文使用平面波展开方法计算了光子晶体线缺陷波导中的色散曲线.研究发现:在色散曲线下边缘处,材料折射率的一个微小变化可以引起传输常数的较大变化,如果工作频率点选择在带下边缘附近,则可以大幅度减小相位移调制型器件调制区域的长度.本文使用时域有限差分方法进一步验证这种增强效应,计算结果表明,对于0.46%的折射率变化,光子晶体线缺陷波导中的相位调制长度仅为均匀媒质中相位移调制长度的11.7%.通过以进一步研究,这种增强效应有望应用与高密度集成光路.     

One dimensional photonic band gap material as an omnidirectional reflector

In this article, the reflection properties in one-dimensional dielectric-dielectric photonic band gap (PBG) structure have been studied. We have used SiO₂ as material of low refractive index and Te as a high refractive index material. Reflectivity of proposed PBG structure is plotted as a function of wavelength and angle of incidence and omni-directional PBGs are computed theoretically. To obtain reflectance, we used transfer matrix method for solving Maxwell’s equations for electromagnetic wave in PBG structures. For a large range of frequency, the PBG structure is found to exhibit omni-directional reflection which can be exploited in devices such as optical resonators, mirrors, etc.     

含左手材料异质结构光子晶体的零平均折射率带隙的展宽

运用光学传输矩阵理论,研究了含左手材料一维二元光子晶体的禁带特性.提出了含左手材料的光子晶体异质结构中零平均折射率带隙展宽的方法.根据此方法设计的异质结构的光子晶体形成的零平均折射率带隙,与一维光子晶体零平均折射率带隙相比,零平均折射率带隙的宽度和相对带隙宽度可以得到显著的拓宽.而且它的零平均折射率带隙的边缘与TM波和TE波相关.这种特性在微型谐振腔、天线基片、同轴波导等方面都具有潜在的应用.     

光学波段菲波纳契序列一维光子晶体纳米膜传输特性研究

为了研究光学波段菲波纳契序列一维光子晶体纳米膜的传输特性,应用传输矩阵方法数值模拟各种情况下的透射率即传输函数随频率的变化.数值结果表明在正入射时,菲波纳契序列一维光子晶体中的禁带宽度、中心位置、数目都与构成序列的项数、组元物理厚度、组成序列组元初始次序、组元折射率差值都对传输特性有较大影响,在可见光区组元折射率差值越大越易形成较宽禁带,进一步研究广义菲波纳契序列一维光子晶体纳米膜的传输特性,发现比典型情况更易在可见光区形成禁带.     

Effect of refractive index of environment medium on electromagnetic mode density in photonic band gaps

The purpose of this work is to analyze the effect of the environmental medium on the density of mode (DOM) in a 1-D photonic crystal. The results show that for a symmetric environment, the DOM changes non-monotonously with an increase in the refractive index of the environment medium, while for an asymmetric environment, the DOM increases monotonously with an increase of the refractive index of the substrate. It is found that low DOM at midgap and high DOM at the band edge can be achieved simultaneously only when a photonic crystal works in an environment where the input medium and the substrate have the same refractive indices. The effect of the refractive index on the surrounding material on the band edge laser is also discussed. PACS 42.70.Qs; 71.20.Tx     

Band gap structure of disordered chiral photonic crystals

Based on the non-symmetric transmission-line method, the band gap structure of disordered chiral photonic crystals (CPC) has been investigated. The influence of the chiral parameters, the disorder, the periods and the refractive index on the band gap structure has been discussed. It is found that the photonic band gap (PBG) in CPC is more obvious than that in the conventional photonic crystals, and the PBG can be increased by increasing the periods or the contrast of the refractive index of the two media. It is also found that the existence of disorder will influence the band edge of the PBG, and such influence will increase with the increment of periods or the contrast of the refractive index of the two media.     

与色散介质毗邻的一维半无限光子晶体表面态

运用Bloch定理和传输矩阵方法,研究了与色散介质毗邻的由两种材料组成的半无限一维光子晶体局域表面态的电场和色散关系.和以空气为背景的一维光子晶体相比,毗邻色散介质的光子晶体表面模色散曲线在一定堆积次序下会在较低的带隙中发生断开,较高带隙中的表面模群速度在不同堆积次序下会有很大差异.当与色散介质毗邻的物质折射率较大时,较高带隙中的表面模群速度较小;与色散介质毗邻的物质折射率较小时,较高带隙中表面模的群速度较大.     

Defect and dope selective of transmission properties of 2D photonic crystal

The effects of the defect and doping on the transmission properties are investigated in two-dimensional photonic crystal (PC) with triangular rods using the finite difference time domain (FDTD) method. The results show that the width and the central position of the photonic band gap (PBG) depend on the thickness of rods with defect or composite-defect, and the refractive index of doped dielectric rods. The transmission properties of composite-defect combined with doping are further investigated. The thinner the nested concentric triangular rod and the smaller the refractive index is, the wider the band gaps is.     

Beyond butterflies—the diversity of biological photonic crystals

When biological photonic crystals are discussed, butterfly photonic crystals are often cited as representative; in fact, numerous diverse biological photonic crystals exist and butterfly photonic crystals have several quirks when compared with others, with the consequence that considering them typical is in many ways unhelpful. In this paper, we give an overview of biological photonic crystals and discuss their typical features, specifically with regard to their periodicities, geometries, chemical compositions, the wavelengths they reflect and their band gaps. The low refractive index contrast and low mean refractive index: a universal feature of biological photonic crystals compared with artificial ones is highlighted and attention is drawn to their comparatively complex band diagrams.     

Enlargement of the omnidirectional reflectance gap in one-dimensional photonic crystal heterostructure containing double negative index material

In this paper, we investigate by theoretical analysis a way to enlarge the frequency range of band gap in one-dimensional heterostructure photonic crystal (PC) made of two PCs alternate stacked by conventional and double negative index material. The numerical results by scattering matrix method (SMM) show that, for the proposed PC with appropriate parameters, there is an omnidirectional photonic band gap (OBG), which is insensitive to incident angle and polarization. The thickness ratio of layers in the second PC is the inverse and identical of that in the first PC, respectively. Two PCs form the PC heterostructures. Moreover, we demonstrate the existence of OBG and notable enlargement of the frequency range of the OBG in proposed PC heterostructure. The reason is that the pass band of one of the two PCs falls into the forbidden band of another PC. Decreasing the thickness of layers but not changing the thickness ratio of layers in the second PC, the frequency range of OBG keeps invariant. However, with the increasing of thickness of layers, the frequency range of OBG gets narrow.