基于光子晶体的表面环谐振器通信工程等专业毕业设计外文翻译-中英文对照.docx

基于光子晶体的表面环谐振器任洪亮 ，张静红 ，秦亚丽 ，刘凯 ，吴哲福 ，胡伟胜，江春， 金耀辉，浙江工业大学信息工程学院 杭州 310023 中国高级光通信系统和网络国家重点实验室，上海交通大学，上海 200240 中国_文章索引文章历史：2010，8，30收到2011，3，30收到修订稿2011，4，1接受2011，4，21网上可用关键字：圆形光子晶体（CPC）表面波导模式（SMW）表面环形波导模式（SMRW）环形谐振器概要：我们设计一个基于光子晶体（PCs）的紧密环型谐振器。这个结构是通过将环形波导一个的表面模式夹在一个二维光子晶体波导的两个平行的表面模式中形成。这种波导的表面模式SMRW是在一个具有高传输效率的环型光子晶体结构的表面上制作的。在某一固定的频率下，在输入波导的表面模式中SMRW作为一个基本的模式被引进，这种SMRW模式由于谐振而加强，光波耦合到输出SMW波导表面模式。这个结果已经通过一个谐振器的模拟结果证明。由于基于光子晶体的表面模式有良好的导波性，所以该表面模式的环型谐振器有非常少量的辐射损失并且可以利用在未来的波分复用（WDM）的光通信系统中。1、介绍光波导环型谐振器可以被用在光滤波器中。光滤波器在光波分复用通信系统，光综合回路和光学计算是非常重要的组成部分1-7。为了利用珍惜的带宽资源，可以通过直接减小圆环半径来有规律地显著地增加自由光谱带范围（FSR）。但是在剥离SOI的环型谐振器上，随着圆环半径的减小辐射损失指数增大，所以在这种情况下圆环最小半径大约是3m4-7。为了减少圆环半径并且获得更大的自由光谱带（FSR）范围，光子晶体圆环谐振器通过Qiang.等人的方法来设计8。通过在正方格子组成的光子晶体的内部设计线缺陷而得到环形谐振器，但是由于这个在环型谐振器的拐角处有很大的传播损失，所以基于六角格子的光子晶体设计这个仪器是很困难的8-12。最近，光子晶体表面光波导被认识到具有高效率的光波透射13-14。光子晶体表面波导制作在一个圆形光子晶体（CPC）结构的表面，通过消除来自CPC的一个同轴层而形成14。这个曲线型的波导被认为有高的能量透射因为该波导带有更光滑的弯曲具有中心对称性和更小不连续性。与在传统的具有六角晶格的光子晶体线缺陷波导相比，曲线形波导更容易利用去建立一个光子晶体环形谐振器。本文是设计基于六角晶格光子晶体表面模式的环型谐振器。对称谐振滤波器是通过将一个SMRW夹进两个平行的SMWs中而形成的。通过增加在六角晶格光子晶体介质和空气间的杆排之间的半径来获得表面波导模式SMWs。环形波导表面模式SMRW是在圆形光子晶体CPC结构的表面上制作的，通过增加圆形光子晶体同轴圆最外层周长的那排半径而得到。这个仪器通过对于完全吸收匹配层的所有边界条件用有限时域差分法计算得到（FDTD）。和环型谐振器的其他表面模式相比3，这种基于六角晶格光子晶体环型谐振结构有非常低的能量损失，输入波导中的大部分光由于谐振转移到输出波导。该仪器结构简单，提供了通道滤波器的可能性，并能用于未来波分复用光通信系统或其他领域。2、环型谐振器的设计我们认为在空气背景中一个半无限六角晶格组成的静电常数=11.6964和一个直径为Db=0.392a圆柱状的光子晶体，这里的a是晶格常数。正如图1（a）所示，在相应的表面状态下（增加最外层表面棒直径至D=0.5a，并且两个最近邻表面杆满足d=0.5a），对表面几何形态进行研究。对光子晶体表面电磁光波的有效局限，必须满足两个条件：表面模式必须在光子带隙中和在光线带下的仅是表面模式的一部分作为考虑13。六角晶格的光子晶体频率在0.28481（c/a）与0.4557（c/a）范围内TM偏振下有基本的禁带，并且在图1（a）所示的条件下，低于光线下存在两种表面模式，其中是指光在真空中的波长。对于图1（B）所示的结构，每个柱在其强度范围内都有一个最大值并延伸到空气中，当进入到有宽度为a的晶体中迅速衰减。对于图1（b）所示增大柱表面的结构条件下，两个表面模式主要分布在柱表面和其在空气中的范围内整个能量分布变化很小14。图1（a）直径为Db=0.392a和介电常数=11.6964杆形成六角晶格的光子晶体沿着投影表面模式的TM模能带结构。表面柱直径D = 0.5a，两个最近邻表面柱之间的距离是d= 0.5a。（b）归一化强度Ez部分表面模式的色散曲线。对于传统的线缺陷曲线波导的光子晶体13，就像布拉格反射曲线镜，光波被波导两边的光子禁带所控制。然而，环型表面模式仅只有一侧的波导周期结构。在SMRW中传播的光波不得不改变他们的大小和方向向量。SMRW大的同心圆距离和小的曲率半径导致波矢量在大小和方向上的突然改变。因此，光波可以更容易的辐射到周围的空气背景中。一个减少辐射损失的的方法是减低表面同心距离dc，然后波导具有了较高的表面有效折射率和高的限制因子。图2（a）显示一半SMRW，SMRW是通过增加表面棒的半径到0.25a由最外层的同心层（即N=8）组成的，在最外层的最近邻表面棒间的距离dc为0.4887a。图2（b）所示，一半SMRW的高功率传输，在dc=0.4887a和dc=0.6109a的透射率分别由粗细的实线来表示。前者比后者在工作频率的改变下有更高的传输效率。这表明由于大的表面棒半径和最近邻表面棒之间的的小距离dc，在有高的表面有效折射率下有高的传输效率。图2。（a） SMRW的一半，环型光子晶体晶胞结构原理图。 （b） 一半SMRW在dc=0.4887a（薄黑线）和dc=0.6109a（厚黑线）处的透射谱。因此，在对称谐振系统利用两个平行波导设计SWMs如图3（a）。这种结构通过在两个平行的SMW之间夹一个SMW。SMRW是在环型光子晶体表面结构上制造的。图3（a）所示二维圆柱杆是直径为0.392a和介电常数为11.6964的环型光子晶体结构，这些柱子有与上述提到的六角结构的光子晶体完全一样的参数。这些环型光子晶体有镜像对称性，并且同心层之间的距离不变都是a。这种结构有六重对称性，每层柱子的数目通过公式6（N-1）得到，这里的N表示层数，N2。通过消除环型光子晶体的一个同心层而形成SMRW。如图3（a）所示在这里，最外层的同心层形成环型波导（即N=8）通过增加表面柱的半径到0.25a，最外层最近邻棒间的距离dc为0.4887a。正如图3（a）所示的对称谐振滤波器是基于光子晶体设计的。共振结构是通过夹在两块平行的SMWs中的SMW形成的。环共振器是通过一块SMRW和两块SMRW被独立的用做输入和输出波导而实现的。为了认识到表面波导模式和环型表面波导模式之间的模式匹配，一般可以考虑两种方法。一个是六角晶格光子晶体和环型光子晶体之间的参数是相似的，包括晶格常数之间的距离等于每个同心层和他们的背景圆柱棒有相同的半径和折射率，很可能SMWs和SMRW模式匹配实现基于类似的晶体结构。另一种就要取决于设计SMRW和 SMWs，包括这些表面棒有相同的半径和最近邻表面柱之间的距离是一致的。在这种情况下，SMRWs和SMRW之间分别的距离为0.5a和0.4887a。类似的模式设计方便地降低表面波导的不匹配是很容易理解的方式。图3。（a） 基于R=7a六角晶格组成的二维光子晶体一个SMRW夹在两个平行SMWs之间形成的环形谐振器的原理图。（b） 当光从输入波导端口A入射时能量在端口B、C、D的透射谱。 （c）频率在0.4165（c/a）f0.4185（c/a）之间的能量透射谱。 （d） 当归一化频率f = 0.41735（c/a）时，谐振环内的电场分布。（e） 频率在0.4275 （c/a）f0.43125 （c/a）之间的能量透射谱。（f） 当归一化频率f = 0.4294 （c/a）时，谐振环内的电场分布。标示在图2（a）中的参数分别是R = 7 a、D = 0.5 a，D = 0.5 a，dc= 0.4887a ，gu= gb = 0.734a。在共振结构，传统的共振微环中波导/环距离是相同的重要参数。谐振滤波器高效没有实现是因为波导/环波导带隙的不适当数值。正如图3（a）所示，SMWs和SMRW之间的带隙分别记为gu和gb。在这里，gu=gb=0.734a。值得注意的是，表面棒必须小心的安置在SMWs和SMRW之间的耦合区域内。在SMWs和SMRW之间的最近杆中心必须是在y轴，否则不能获得SMWs模式和SMRW模式之间的良好的耦合。究其原因可能是是两个表面模式节点与相应的耦合区域相一致，导致他们耦合现象的发生。当一个基本的TE模（电场区域垂直于x-y平面）被引入输入波导，TE波将会与SMRW相耦合，并且激发基于这些最外层同心圆波长表面棒的表面模式。在一定的频率下，SMRW内的表面模式将会因为共振而增大，并且能量被转移到输出波导中。环的FSR（自由光谱带）可以从以下公式中获得： FSR= （1）这里c是光在空气中的速度，neff是环的有效折射率，R是环的半径。如图3（a）所示，端口A作为光源发射端，三个时间检测器检测传输光波能量分别设置在端口B、C和D。然后，设计的装置对在所有相应的将边界有完全吸收条件下进行了有限差分法计算。归一化能量传输光谱通过将端口B、C和D的能量总和作为总输入的能量。图3（b）描绘的传输谱谐振腔半径的环R = 7 a，这里的能量传输端口B、C和D分别用厚实线，虚线，薄曲线表示。在共振频率下，绝大部分能量通过环谐振腔从输入波导转移到输出波导。FSR的数值通常通过环谐振器传输光谱获得。即FSR之间应满足的相邻两个共振峰频率间隔，在这里是0.00602（c/a）。所以根据方程（1）环的有效折射率neff是3.7768。图3（c）描述的是频率在0.4165（c/a）f0.4185（c/a）之间的能量传输谱。D端口的下降谱线不再是洛伦兹线性曲线是显然的，这可能是因为在SMW和SMRW之间的模式不匹配引起的。谐振器有大约6474的品质因子，这是相对于其他类型的环谐振器最高的品质因子结果，可以通过增大环谐振器的半径来改善品质因子。图3（d）阐述了在环谐振腔半径为环R = 7a ，频率为f = 0.41735（c/a）电场分布。通过光波端口A在f = 0.41735（c/a）下，输入波导被激活。SMRW条件下共振发生和绝大部分能量转移到输出波导。你可以看到，在SMRW的共振频率下电磁场强烈增强。然而，在共振发生时有少量光辐射到周围的空气背景中，这导致波导表面模式的少量辐射损失。这些光波辐射在两个平行SMWs之间反复地反射。从图3（d）中得在两个平行波导间有少量的能量分布在空气背景中。图3（e）显示的是频率在0.4275（c/a）f0.43125（c/a）之间的透视图。有趣的是， 在端口C频率f= 0.4294（c/a）前端支配下降了，对于传统的单微环共振结构后方下降共振的支配很明显地不同。在某些频率下，前端下降提高了，到目前为止具体机制还不了解。在这种情况下，在端口A入射波在只会产生顺时针传播的共振模式，并且入射波和其他逆时针传播的模式没有直接的耦合关系 15。然而，顺时针和逆时针传播的谐振模式由于相互耦合而相关。逆时针方向共振模式可以通过两个共振模式之间的耦合关系改进，大部分的光波在端口C前端下降。图3 （f）阐述了在半径为环R = 7a，频率f = 0.4294（c/a）的环谐振腔电场的分布。图4。（a） 在R = 4a时环谐振器原理示意图。（b）在R = 4 a时在端口B、C和D的透射谱。（c） 频率在0.41 （c/a）f0.4175 （c/a）之间的能量透射谱。 （d） 当归一化频率f = 0.41386 （c/a）时，谐振环内的电场分布。标示在图3（a）中的参数分别为R =4a、D = 0.5 a，d = 0.5a，dc = 0.5027a和gu= gb = 0.644a。图4（a）显示了半径R = 4 a的对称谐振器原理图，在最外层最近邻表面柱之间的距离调整到dc= 0.5027，并且SMRW /SMW距离的改变到gu= gb = 0.644a。图4（b）显示的是在端口B、C和D的透射光谱，它们分别用厚实，点虚线形和薄实曲线表示。很明显，从图4（b）中得到FSR是0.01（c/a），对于SMRW的有效折射率neff=3.979的。图4（c）显示的是频率在0.41（c/a）f0.4175（c/a）之间的透射特性，谐振腔品质因子有1223左右。3、结论我们呈现了一个基于电介质PC的表面模式环谐振器的设计。如果在频率f = 0.41386 （c/a）下波长是1550nm，晶格常数是641.5m，所以SMRW半径为R = 4 a大约是2.5m。与环谐振器其他表面模式相比3，计算结果表明，环形谐振器有较小量的辐射损失的因为表面模式有很好的波导特性。这种结构提供了通道滤波器的可能性，并可用于未来光波分复用通信系统。4、鸣谢这项研究受到中国国家自然科学基金 （Nos.60978010、60907032、and 60825103)， 浙江省自然科学基金（No.Y1090169)，浙江工业大学基金 （No:0901103012408)，区域光纤通信网与新型光通信系统国家重点实验室开放课题基金（No.2008 sh07)。参考文献：1 S. 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Symp. 2009, 281, 119125DOI: 10.1002/masy.200950716119Latex Film Formation in the Environmental ScanningElectron MicroscopeKalin Dragnevski,*1 Athene Donald,1 Phil Taylor,2 Martin Murray,3 Simon Davies,3Elizabeth Bone3Summary: Environmental scanning electron microscopy (ESEM) was used to study the film formation mechanisms and extent of coalescence of three acrylic latex com- positions with different glass transition temperatures (Tg), here defined as standard- low Tg, standard-high Tg (both carboxymethyl cellulose- stabilised) and novel (stabilised with a novel polysaccharide derived from agricultural waste). The ESEM analysis revealed that the microstructure of the standard low-Tg system consisted of individual particles in dispersion and upon evaporation a continuous film formed, whereas in the case of the standard - high Tg latex particle deformation was not observed, but particle aggregation resulted in the formation of crystal-like structures that have formed via the formation of stacking faults. However, in the case of the novel system the microstructure consisted of individual particles and clusters and during evaporation a discontinuous film formed with voids present within its structure and some of the clusters accumulating on the surface of the specimens.Keywords: ESEM; film formation; polymer latexIntroductionPolymer latices, with their wide range of applications, have been the subject of many theoretical and experimental studies. When used for its traditional applications, i.e. as paint or adhesive, the latex is applied in its wet state to a surface and allowed to dry and form film under ambient conditions. Therefore, conventional electron micro- scopy, with its extreme drying and sample preparation requirements, will not be suitable for the examination of latices in their natural wet state. On the other hand, environmental scanning electron micro-scopy1, which offers the possibility of1 Sector of Biological & Soft Systems, Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge, CB30HE, UKE-mail: kd281cam.ac.uk2 ICI Paints, Slough, Berkshire, SL2 5DS, UK3 ICI Wilton Applied Research Group, The WiltonCentre, Redcar, TS10 4RF, UKimaging wet and insulating specimens, has been successfully used in the study of a number of systems and dynamic processes including latices and film formation.26ESEM is based on the use of a multiple aperture graduated vacuum system, which allows specimens to be imaged under water vapour or other auxiliary gases, such as nitrogen or nitrous oxide.4 In this way, the chamber can be held at pressures usually in the range of 110 Torr7, while the gun and column remain at pressures of 7.5 10 7 Torr. Moreover, by using acorrect pumpdown procedure8 and by controlling the temperature of the speci- men, which in the ESEM is usually done by using a Peltier stage, dehydration can be inhibited and hence samples can be imaged in their natural state. Furthermore, bytaking into consideration the saturated vapour pressure (SVP) curve for water as a function of temperature8 and by increas- ing the temperature of the specimen or reducing the chamber pressure, it is possi-Copyright 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim120Macromol. Symp. 2009, 281, 119125Figure 1.Schematic representation of an idealized film formation process. Adapted from Keddie et al. to include the intermediate Stage II .ble to produce evaporation conditions within the specimen chamber, which allows examination of the process of film forma- tion.As mentioned above, polymer latices are important industrial products and the subject of many research studies. Latex, which is an example of a wet insulating material, can be defined as a colloidal suspension of spherical polymer particles with varying diameters. When water is allowed to evaporate from the system, the aqueous suspension undergoes a series of transformations, which result in the forma- tion of a continuous dry polymer film. This process, known as film formation, contains four main stages that can be described asfollows:917 Stage I dispersed suspensionof polymer particles; Stage II concen- trated suspension of particles in contact with each other, surrounded by solvent- filled interstices; Stage III ordered array of deformed particles; Stage IV a molecularly continuous and homogeneous film formed as a result of polymer interdiffusion.In 1995, Keddie et al. 4 used environ-mental scanning electronmicroscopy (ESEM) and Multiple-Angle-of-Incidence Ellipsometry (MAIE) in the study of latex film formation. They concluded that an intermediate stage, between II and III, has been omitted in the conventionaldescriptions.917 The stage, defined as II , is characterized by a randomly packed array of deformed particles which still contain water-filled interstices. A schematic representation of the process is shown in Figure 1.More recently, Keddie et al.18,19 inves-tigated the possibility of creating hetero- geneous films, by mixing carbon nanotubes (CNTs) with waterborne polymer particles. It was found that the mechanical properties of the nanocomposite coatings can be greatly improved, while maintaining their optical clarity. However, it is important to note that all of the above studies were carried out using continuous polymer films.In this paper we present the results from an ESEM investigation into the film for- mation mechanisms of novel acrylic latex, which has been stabilised by using a new polysaccharide, derived from agricultural waste, and two standard polymer systems, where the conventional carboxymethyl cellulose (CMC) has been used as a stabiliser. The novel polysaccharide con- sists of a number of monosaccharides (including arabinose and xylose) formed from five- and six-membered rings and has a low molecular weight, only a few thousand a.m.u.s rather than the hundreds of thousands found in cellulose for exam- ple. The polysaccharide also contains aCopyright 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimwww.ms-journal.deMacromol. Symp. 2009, 281, 119125121significant amount of interfacially active protein 15%. It is suggested that the initial latex particle stabilization comes from the protein component and ultimately the polysaccharide component stabilises the latex particles by adsorbing on their surface, rather than by chemically grafting on the growing polymer particles, which is the case for the conventionally used CMC. Initial examinations20 have indicated that the novel latex can form film without theaddition of coalescing solvents, which, as suggested above, on one hand would provide an alternative method for the production of VOC-free architectural coat- ings and, on the other, would comply with the stringent EU and DEFRA regula- tions.21Materials and MethodsThree aqueous latex compositions, sup- plied by ICI Plc, based on copolymers of methyl methacrylate (MMA) and 2-ethyl- hexyl acrylate (2-EHA) were studied. In this paper the latices stabilised with carbox- ymethyl cellulose (CMC) will be referred to as standard-low and high Tg; the other stabilised with the new polysaccharide as novel. The three latices were initially about55 wt% polymer. The glass transition temperatures (Tg) of latices were deter- mined by differential scanning calorimetry (DSC), carried out on dry specimens, using a Perkin Elmer Pyris 1 instrument. The measured temperatures were 274 K for the standard-low Tg, 328 K for the standard- high Tg and 280 K for the novel latex.The microstructural analysis was carriedout on an FEI XL-30 environmental scanning electron microscope equipped with a Peltier stage. Wet samples from the above formulations were placed onto the cooling stage in the microscope chamber at a temperature of ca. 274 K. Anevaporation-inhibitingpumpdown sequence was then performed, with the ambient air progressively replaced by water vapour. Once the purging cycle was com- pleted, water vapour pressures and workingdistances of 3.54.5 Torr and 9.511.5 mm were set, which provided optimal imaging environments, i.e. sufficient resolution and minimal beam damage. Imaging of the specimens was carried out at an accelerat- ing voltage of 10 kV. Increasing the tem- perature of the specimens by 1 or 2 degrees above the starting temperature of 273 K, as explained above, resulted in further dehydration of the latices, which allowed examination of the process of film formation.Results and DiscussionPrior to considering the results from the ESEM examination, it is important to note that when we refer to latices as being wet, some water has in actual fact been removed from the surface of the specimens in order to obtain better quality images. Keddie et al.1,4 used a similar approach in the study of latex film formation by means of ESEM. It was found that despite the fact that some of the surface water had been removed, the bulk of the samples remainedwet.Standard Latex low TgFrom the ESEM images of the standard- low Tg latex (Figure 2), it can be seen that under wet conditions (Figure 2a) the microstructure of the specimen consists mainly of randomly distributed individual particles with an average size of ca. 300 nm. Due to the fact that some of the water has already been removed, as explained above, some of the polymer particles are in contact. Despite that, they are still physi- cally distinct, i.e. no significant deformation has occurred, and therefore it can be concluded that the latex is in Stage II/II . By increasing the temperature of the specimen (Figure 2b), water evaporation takes place, which resulted in the formation of a continuous polymer film. However, due to the fact that not all particles have lost their ident