【作者】 郝锐；

【导师】 李志全；

【作者基本信息】 燕山大学 ， 控制科学与工程， 2013， 博士

【摘要】 自从1996年被首次制备成功以来，光子晶体光纤(PCF)就以其传统光纤无法实现的独特且优越的性质受到国内外广大学者的普遍关注。目前，光子晶体光纤的应用研究已经扩展到光通讯、光传感、光电检测、光纤激光器及光学医疗器件等众多重要的领域。随着应用领域不断扩展，高新技术的进展使研发各种高性能的光子晶体光纤以及新型光子晶体光纤器件已经成为一种迫切的需要，因此，开展PCF的特性及应用的理论研究具有重要的学术价值和广阔的应用前景。本文以折射率导光型高双折射光子晶体光纤为重点，利用多极法建立理论模型，对几种新结构高双折射PCF的传输特性进行了细致的理论研究；提出了两种新型双芯PCF偏振分束器，采用全矢量有限元方法建立模型并进行了深入的理论分析，主要的研究内容如下：首先，提出了六边形包层椭圆纤芯的光纤结构，分析了空气孔径和纤芯的椭圆率对双折射的影响，结果表明这类结构的包层对称性很高，双折射主要是由椭圆形的纤芯引起的。孔径对双折射的作用并不明显但椭圆率产生的影响很显著，当椭圆率分别为3:2和2:1时，双折射可以达到10-3量级；提出了空气孔椭圆形分布的光纤结构，分析了孔径、孔层数和椭圆率对双折射的影响，结果表明这种结构的不对称性要高于六边形包层椭圆纤芯的结构，在椭圆率同为4:3时，这种结构的双折射达到了10-3量级。同时，椭圆包层结构的不对称性主要由孔分布的椭圆率决定，椭圆率越大，结构的不对称性越强，则双折射越高；提出了三种压缩的六边形光纤结构，分析了孔径和孔间距对双折射的影响，结果表明孔间距的影响效果更显著，间距越小则双折射越高。增大孔径或缩小孔间距可以提高结构的不对称性，从而增强双折射。这类结构通过选择合适的结构参数可以在1.55μm波长处实现1.544102的高双折射其次，利用多极法对椭圆包层结构、压缩六边形结构和类熊猫型压缩六边形结构的色散、等效模式面积和非线性系数进行了模拟分析，重点分析了结构参数对这些特性参量的影响。对于椭圆包层结构，改变孔层数、孔径和椭圆率来分析传输特性的变化过程；对于压缩的六边形结构，分析了孔径和孔间距对三个特性参量的影响，并对比了不同孔间距时的模拟结果。分析结果表明，结构参数对色散和非线性都有明显作用，调节结构参数可以产生振荡形式的色散和较高的负色散，且结构的不对称性越高，非线性效应越强。类熊猫型压缩结构在1.55μm波长处的非线性系数可达到69.54W-1km-1。最后，基于模式干涉原理提出了两种新型的双芯PCF偏振分束器，一种是包层为八边形和矩形相结合的结构，利用全矢量有限元法分析了基模场的分布和结构参数对双折射、耦合长度的影响，经过优化后模拟了归一化传输功率和消光比，得到了长度为314μm的分束器结构，在1.55μm波长处的消光比约为-50.5dB，消光比为-10dB的带宽约为170nm，消光比为-20dB的带宽为60nm；另一种是由软玻璃SF6构成的矩形结构双芯PCF偏振分束器，利用全矢量有限元法分析了基模场的分布和结构参数对双折射、耦合长度的影响，选择合适的结构参数可以得到长度为281μm的偏振分束器，在波长1.55μm处的消光比可达到-45.42dB，消光比为-10dB的带宽为90nm，消光比为-20dB的带宽为32nm。更多还原

【Abstract】 Since successfully fabricated in1996for the first time, photonic crystal fibers (PCF)have received wodespread attentions from a lot of researchers all over the world due tothose unique and excellent properties that can’t be realized in conventional fibers. Atpresent, applications of PCFs have expanded into many important research domains, suchas optical communications, optical sensing, photoelectric detection, optical fiber lasers andmedical devices, etc. With application fields gradually extending, to develop highperformance PCFs and novel devices based on PCFs has become an urgent demand.Therefore, carrying out theoretical studies on PCF characteristics and applications is ofgreat academic values and wide application prospects.Focusing on index-guiding highly birefringent PCFs, propagation properties of severealnovel PCF designs are thoroughly investigated theoretically by employing multipolemethod. Two novel dual core PCF polarization splitters are presented and the full-vectorfinite element method is adopted to analyze and optimize the structures, and main researchcontents are listed below:Firstly, PCF structures with the hexagonal cladding and elliptical cores are proposedand impacts of air hole sizes and the core’s ellipticity on birefringence are analyzed, andresults indicate claddings of these designs are highly symmetrical so birefringence ismainly caused by elliptical cores. Effects of hole sizes on birefringence are trivial butellipticity of the core has great impacts. With ellipticity of3:2or2:1, birefringence is onthe order of magnitude of10-3; Structures with air holes in elliptical configuration arepresented and effects of air hole sizes, the number of air holes and ellipticity onbirefringence are investigated, and results show that symmetry of these structures is higherthan that of structures with triangular lattice and elliptical cores. With ellipticity of4:3,birefringence of these structures is on the order of10-3. Meanwhile, asymmetry ofelliptical claddings is mostly determined by ellipticity of air holes’ distribution, the largerthe ellipticity is, the more asymmetrical these structures are and the higher birefringence is;Three squeezed hexagonal PCF designs are proposed and impacts of air hole sizes andhole pitch on birefringence are analyzed. Results indicate hole pitch plays a moreimportant role on birefringence than hole sizes, and decreasing the hole pitch can enhancethe asymmetry of the ocre and cladding, which leads to higher birefringence. By selecting proper structural parameters, the highest birefringence of1.544102can be realized atthe wavelength of1.55μm.Secondly, using multipole method, numerical analysis on dispersion, effective modalarea and nonlinear coefficient of PCFs with elliptical claddings, squeezed hexagonalcladdings and panda-like squeezed hexagonal claddings is carried out. As for the ellipticalcladding structres, impacts of the number of air hole rings, hole sizes and ellipticity ondispersion, effective modal area and nonlinear coefficient are analyzed; As for thesqueezed hexagonal structures, hole size and hole pitch both affect those transmissionproperties, and results with different hole pitches are compared. Results show thatstructural parameters affect all those properties, leading to normal and oscillatingdistributions, zero dispersion points in multiple communication wavebands and largenegative dispersion values. Moreover, structures with higher asymmetry have strongernonlinearity, for example, the nonlinear coefficient of panda-like squeezed hexagonaldesign is around69.54W-1km-1at the wavelength of1.55μm.Finally, based on the modal interference principle, two novel dual core PCF polarizationsplitters are proposed. The first one’s structure is a combination of octagonal andrectangular claddings, and its fundamental modes’ distribution and impacts of parameterson birefringence and coupling length are analyzed by using full vector finite elementmethod. After optimization the normalized power and extinction ratio of this design arenumerically investigated, moreover, the extinction ratio at1.55μm is around-50.5dB, andthe bandwidth at the extinction ratio of-10dB is170nm,60nm at the extinction ratio of-20dB. The second one is made of soft glass SF6with circular and elliptical air holesarranged in rectangular lattice, and by selecting proper structural parameters a281μm longpolarization splitter is realized. The extinction ratio at1.55μm is around-45.42dB, andthe bandwidth at the extinction ratio of-10dB is90nm,32nm at the extinction ratio of-20dB.更多还原