Wave Manipulation with Functional Metasurfaces

Abstract

Recent developments have shown that the metasurface approach of tailoring wavefronts is a powerful tool to alter the propagation characteristics at the interface and it has attracted great interest because of its versatility and simplicity in fabrication. The ability to drastically modify the propagation characteristics by simply placing an array of patterned two-dimensional optical scatters on the surface offers a tremendous opportunity for novel applications in optics. The aim of this dissertation is to investigate novel applications that are enabled by this newly emerging metasurface.
To achieve our goal, we firstly develop the electrostatic analogue method and a general framework for an artificial electromagnetic boundary (AEB), described by the impedance matrix as constitutive parameters like bulk metamaterials. Such a generic design scheme of metasurface devices is investigated for realizing asymmetric transmission, shaping wavefronts, gradient-index lens, transformation optics (TO), carpet cloak and illusion optics applications. Besides, we extend to the acoustic case and realize symmetric and anti-symmetric coherent perfect absorption (CPA), and beam shifting effect with enhanced transmission by designing a single layer of metamaterials.
Particularly, in order to ease the design of metasurface devices for novel applications, we employ the developed the AEB method to completely describe the response of the metasurface to electromagnetic (EM) radiations. In this way, we firstly design a 1D Gradient-metasurfaces waveguide for asymmetric transmission, and then extend to design 2D metasurface-loaded waveguides for realizing a constant zero-index medium for wave collimation, gradient-index profiles lens, a carpet cloak and a wave bender. The particular method is to introduce the effective medium description of bulk metamaterials to the regime of metasurfaces with a few constitutive parameters. Furthermore, we present a more flexible design scheme by only a single sheet of metasurface, which enables external cloaking and illusion optics with very good performance. These investigations offer a macroscopic approach in designing functional metasurface devices and can serve as a useful source for future experimental developments. On the other hand, consider the analogy between EM and acoustic wave, we extend optical concepts to the acoustic domain. The first one is that CPA with a pair of in- (0) and out-of-phase (π) incident beams are demonstrated by designing metamaterial structures with a resonating bulk modulus and density response in acoustics (or equivalently resonating electric and magnetic response in optics). Then, an acoustic beam shifter with enhanced transmission is fabricated and demonstrated by combining principles of TO map theory and extraordinary transmission using perforated metamaterials, which is geometrically tunable.

Date of Award	6 Sept 2016
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Sai Tak CHU (Supervisor) & Jensen T H LI (Supervisor)