Metamaterials with low symmetries

Abstract

Metamaterials, with subwavelength artificial atoms, have shown great promise in manipulating electromagnetic waves. Recent development of chiral metamaterials with electro-magnetic coupling enhance circular dichroism, asymmetric transmission and optical activity, showing that symmetry breaking can play a vital role in the optical properties of metamaterials. In this dissertation, we further investigate metamaterials with generally low symmetries. By breaking various spatial symmetries or parity-time symmetry, it allows cross-coupling between different polarizations and hence a wider spectrum of exotic optical phenomena including complete polarization conversion, asymmetric transmission for linear polarization, coherent perfect absorption, and optical phase transition. (1) By using metamaterial atoms with broken rotational and mirror symmetries, we demonstrate strong asymmetric transmission for linear polarization from the anisotropy and chirality induced from spectrally detuned resonances; (2) By using metamaterial atoms with tilted anisotropy from the incidence plane of wave propagation, we extend the framework of transformation optics from conventional coordinate transformation to include field transformation, which can be utilized to achieve all-angle complete polarization conversion and all-angle perfect magnetic conductor; (3) By using metamaterials with well-controlled coupling between bright electric and dark magnetic atoms, we establish a passive route to obtain a parity-time symmetric Hamiltonian. The spontaneous breaking of this parity-time symmetry allows us to demonstrate phase transitions of optical properties such as coherent perfect absorption in a passive system. These investigations about metamaterials with low symmetries allow us to construct metamaterials with polarization-enabled or tunable functionalities and are potentially useful for designing antenna substrates, tunable metamaterial absorbers, polarization convertors, and resonators with tailored boundary conditions.

Date of Award	16 Feb 2015
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Jensen T H LI (Supervisor) & Sai Tak CHU (Supervisor)