【作者】 余振中；

【导师】 冯一军；

【作者基本信息】 南京大学 ， 电磁场与微波技术， 2012， 博士

【摘要】 2006年,J. B. Pendry教授提出了变换光学理论,受到了相关领域学者的广泛关注。变换光学可用于自由控制电磁波的传播,该理论最重要的应用是用以设计电磁隐身斗蓬和隐身地毯,此外应用变换光学还可设计其他新颖的电磁波调控电磁器件,如电磁波集中器、旋转器、波束分束器等等。当前隐身斗篷的研究关键是如何实现和简化隐身斗篷的结构。变换光学理论是基于麦克斯韦方程形式不变性得到的,可以运用于各类电磁波的传播调控,当然也包括对表面等离激元(SPPs)的调控。近年来,运用变换光学理论来调控表面等离激元的研究正在逐步开展。鉴于上述发展趋势,本文着重开展了变换光学及其在隐身斗蓬和表面等离激元传播中的应用研究。首先根据变换光学和散射相消理论,提出了多层均匀各向同性材料隐身斗蓬的优化设计方法,并研究和设计了几种基于变换光学的新型电磁波调控器件；其次我们将变换光学进一步拓展到表面等离激元的传播调控中,设计并分析了表面等离激元波束控制器、分束器、弯折装置以及全向吸收器,最后提出了界面不连续结构上的表面等离激元耦合器和纵向压缩器的概念。本论文的主要内容和研究成果包括如下几方面：(1)提出了一种由多层均匀各向同性材料构成的隐身蓬的优化设计方法。通过严格电磁散射计算和遗传算法优化设计,我们得到了层数较少的隐身斗篷结构,分别给出一个六层等厚材料的隐身斗蓬和一个由两种材料交替构成的五层隐身斗蓬的设计实例,均具有很好的隐身效果。在考虑等离子材料损耗影响的情况下,通过采用引进增益材料进行补偿的优化方法,对低损耗和高损耗两种情况分别进行了讨论,也获得了较好的隐身斗篷效果。(2)提出了一种由多层均匀各向异性材料实现的电磁集中器的优化设计方法。理论上分析推导了柱坐标系下各向异性材料中的电磁场表达形式和散射计算公式,并将其运用于多层均匀各向异性材料构成的电磁集中器的优化设计中,获得了预期的器件性能。(3)运用变换光学方法,提出了360度无畸变全景透镜的设计方案,该器件能够将360度视角的光线压缩到一个180度视角的区域内。分析计算了该器件的材料参数,并对所设计全景透镜的电磁性能,在多种情况下进行了仿真验证,获得预期的效果。(4)将变换光学理论和设计方法运用到表面等离激元调控器件的设计方法中,提出了表面等离激元波束控制器、分束器以及弯折装置的设计方案,通过电磁分析分别验证了这些器件的性能。针对表面等离激元调控器件的实现问题,运用改变金属表面介质覆层的厚度来调节SPPs的有效折射率,设计了可实现的表面等离激元弯折装置以及全向吸收器,并对这些表面等离激元调控器件进行了三维电磁波全波仿真验证。(5)基于补偿媒质和折叠几何的变换光学,提出了金属/介质界面缝隙上表面等离激元的耦合传输方法。分别分析了利用补偿媒质和变换光学设计方法使SPPs在横向偏移、纵向偏移或轴向倾斜的金属/介质界面缝隙上耦合传输。最后,我们还提出了SPPs的纵向压缩器件,可以用来抑制金属表面附近存在障碍物时SPPs的散射,并能有效提高SPPs的传输效率。更多还原

【Abstract】 In2006, Professor J. B. Pendry proposed the theory of transformation optics, which has been received wide attention from researchers of related fields. Transformation optics can be used to freely control the propagation of electromagnetic (EM) wave. The most important application of this theory is EM invisibility cloak and carpet, and other novel EM devices are proposed later, for example the EM concentrator, rotator, splitter and so on. Currently, the research of invisibility cloak is focused on the realization and reducing the complexity of the cloak. As transformation optics is based on the form-invariant of Maxwell’s equations under different coordinate transformations, it applies to all EM waves including the surface plasmon polaritons (SPPs). Recently, some efforts have been made in successful application of transformation optics to the efficient manipulation of the SPP waves.In the view of above development trend, this dissertation mainly studies the transformation optics and its application in the invisibility cloak and SPPs propagation. Firstly, we proposed the optimized design of invisibility cloak with layers of isotropic materials on the basis of transformation optics and scattering cancellation theory, and then several novel transformational devices were studied and designed. Secondly, we extended the transformation optics to surface plasmonic waves, and designed several surface plasmonic devices, including SPPs squeezer, splitter, bend and omni-directional absorber. At last, we proposed the concept of plasmonic coupler for the discontinuous dielectric/metallic interface. The main contributions of this dissertation are listed below:(1) We presented optimized design of cylindrical invisibility cloak composed of minimum number of layers of homogeneous and isotropic materials. Through rigid EM scattering calculation and optimization based on genetic algorithm, we achieved multilayered invisibility cloak, such as six-layer cloak with uniform thickness and five-layer cloak with alternating of two materials. We demonstrated that the optimized designs could achieve nearly perfect cloaking performance. When considering the losses of the plasmonic material in the cloak, we analyzed the conditions of high-loss and low-loss through introduction of gain medium to compensate the losses, and also achieved good performance.(2) We presented an optimized design of EM concentrator with layers of homogeneous anisotropic materials. We theoretically analyzed EM wave expressions and scattering formula in anisotropic materials under the cylindrical coordinate system, which was then used to optimally design the concentrator with layers of homogeneous anisotropic materials. At last, we obtain the expectant functionality of the device.(3) Using the method of transformation optics, we proposed the design scheme of a360°panoramic lens without aberration, which can compress the light from a360°view angle into a180°view angle. The material parameters of the panoramic lens are analyzed and calculated. Through simulations under several different cases, we validated the expected performance of the panoramic lens.(4) We applied the theory and design method of transformation optics to the SPPs manipulating devices. The SPPs squeezer, splitter and bend are proposed and validated by three-dimensional (3D) full-wave EM simulations. For the realization of the SPPs devices, we can adjust the effective refractive index of the SPPs through varying the thickness of the cladding material on the metal. We designed the realizable SPPs bend and omni-directional absorber. The functionality of these proposed plasmonic devices has been verified using3D full-wave EM simulations. (5) Based on the complementary media and folded-geometry transformation optics, the coupling of SPPs through the gap in the dielectric/metallic interface has been proposed. We analyzed the SPPs coupling when the gap in the dielectric/metallic interface has transverse excursion, longitudinal excursion or even the axial tilt. At last, we presented the SPPs longitudinal compressing device, which can be used to suppress the scattering from the obstacle closely above the metal surface and effectively increase SPPs transmission efficiency.更多还原