Transformation Optics And Application In The Invisibility Cloak And Surface Plasmon Polaritons Propagation

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.