Study Of Invisibility Cloak In Visible Light Based On Homogeneous Transformation Optics Theory

Invisibility has been a long-cherished dream of human being. Thanks to the theoretic works of "metamaterials" and "transformation optics", it becomes possible to make object perfectly invisible. Since then, great progress has been reported and invisibility is now one of the hottest research areas in electromagnetism, physics, photonics, materials science and related inter-discipline. This dissertation addressed the design and implementation of invisibility cloak in visible light based on homogeneous transformation optics theory.In the first part of the dissertation, we introduce the research status of invisibility cloak. The constitutive parameters of the ideal cloak obtained through transformation optics are often inhomogeneous and include extreme values, which increased the difficulty in experimental realization, in particular, to obtain the required parameters in optical spectrum. So far, the experiments on isolated cloaks are mostly in microwave frequencies and rarely in optical frequencies.The main work of this dissertation is detailed as follows:1. We propose a homogeneous transformation method to design isolated invisibility cloak. In practical, inhomogeneous constitutive parameters is hard to realize especially in optical frequency range. By using homogeneous transformation method, the constitutive parameters can be homogeneous and contain no extreme values, which make it easier for experimental realization.2. By using homogeneous transformation method, the method to design the polygonal isolated invisibility cloak is suggested. We also suggest the method to design the isolated acoustic cloak based on homogeneous transformation acoustics.3. Based on the above method, an isolated invisibility cloak in TM polarized visible light is demonstrated in this dissertation. By using natural anisotropic materials, a hexagonal isolated cloak which works for six incident directions is fabricated for experimental verification, the performance of which is validated in a broadband visible spectrum for TM polarized light. The realization of an isolated invisibility cloak in the visible light is an important step towards achieving a fully movable invisibility cloak.4. By abolishing the requirement for phase preservation and make the cloak effective only on several incident directions, the constitutive parameters of the invisibility cloak can be further simplified and isolated invisibility cloaks in full polarized visible light are demonstrated. By using isotropic materials, a cloak works in incoherent natural light for large objects is experimental verified. Further more, to make the invisibility cloak works for unidirection, a full polarized unidirectional invisibility cloak in visible light is also verified.5. At last, a broadband subwavelength imaging device based on transformation optics is proposed and demonstrated in this dissertation. The resolution of a conventional optical device has been restricted due to the diffraction limit, the previous subwavelength imaging using hyperlens work only in a narrow frequency band. We demonstrated that subwavelength imaging can be achieved in a broad frequency band using non-resonant metamaterials which is fabricated by metallic closed-rings with a broadband magnetic response.