Revisit transformation-optics based metamaterial design

• Main Author: Yao, Huang
• Other Authors: Luo Yu
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: https://hdl.handle.net/10356/155817
• Institution: Nanyang Technological University

The development of transformation optics (TO) provides a powerful theoretical tool which can transform space and fields, and control electromagnetic wave propagation. This extraordinary feature significantly promotes the applications of TO theory in the design of versatile metamaterial devices including invisibility cloak, absorber, retroreflector, superlens etc. However, since the complex spatially changing refractive index is applied to control the light propagation, the metamaterial device usually ends up with bulky lossy material and involves complicated structure design. Such complexities significantly prevent TO to real world applications. In this thesis, we revisit the TO scheme focusing on untackled challenges. The contributions of this thesis include: 1. We propose a general conformal transformation approach to design polarizationrobust mid-infrared carpet cloak with minimized lateral shift. In order to completely eliminate the lateral shift, we propose an illusion device that can make an elliptic defect reflect like a flat mirror. By varying the defect property, an impedance-matched flat absorber is realized under the same coordinate transformation. These devices all require only isotropic and positive refractive index, which can be easily implemented by drilling holes on the dielectric slab. 2. We study the mid-IR ideal omnidirectional invisibility cloak by transformationinvariant metamaterial. This particular highly anisotropic metamaterial is achieved through metal-dielectric stacking structure. Apart from invisibility cloak, this transformation-invariant metamaterial is extended to construct mid-IR retroreflector and superlens. Besides, a general scheme for ultrathin plasmonic adaptor design is also proposed based on transformation-invariant metamaterial. 3. We apply this transformation-invariant metamaterial to realize finite electrostatic invisibility cloak. We demonstrate theoretically and verified experimentally its omnidirectional property and robust cloaking performance under arbitrary input source. We believe our metamaterial devices design scheme may trigger great interests for guiding other optical devices designs.