School of Physics - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemFluorescent defects and optical structures in metal oxides( 2016)The emission properties from fluorescent defects and manipulation/control of this light were the main themes of this thesis. It begins with the exploration of the emission properties of a radiating dipole within a spherical nanoparticle (NP) and how it is affected by the surrounding refractive index environment. It is important to address this topic as it can give researchers preliminary insight to their system using relatively simple numerical method and modelling. The radiating dipole is treated classically and the finite-difference time-domain technique is used to solve the electrodynamics of systems with optically relevant environments. This method is not restricted to just the environments presented within, but can be generalised to any arbitrary system. The total radiated power from the dipole can be significantly affected by: the refractive index of the NP, the size of the NP and the surrounding refractive index environment of the NP. Experimentally relevant refractive index distributions were considered in this thesis. The mechanism of visible and infrared fluorescence from optical defects within metal oxides has been highly debated where materials scientists do not have a general consensus on the origin. One aspect that is agreed upon is that the visible emission is due to native point defects within the crystallographic structure. This thesis will focus on the optical characterisation of fluorescence defects in promising optical materials of zinc oxide (ZnO) and titanium dioxide (TiO2). The controversy begins with the abundance of fabrication methods for ZnO and TiO2 that inevitably introduces different defects based on the experimental conditions. The fluorescence characterisation by materials scientists involves measurements that sample many defects, due to a large spot size in commercial set-ups, and therefore individual defect signal is lost. The defects in ZnO and TiO2 explored here will be characterised using confocal microscopy, a high-resolution optical technique. This gives the ability to address individual defects with an appropriate resolution to isolate single defects. The fluorescence defects from a few morphologies of ZnO and TiO2 were shown to exhibit room-temperature single-photon emission and these were furthered characterised by investigating their: photoluminescence spectrum, photodynamics, power saturation and lifetimes. Finally, this thesis explores the control and manipulation of light through a structured environment which is central to the operation of an integrated optical circuit. An important integrated component known as an optical microcavity which confines and traps was explored in this thesis. A deterministic algorithm for an ultrahigh-Q nanobeam cavity was explored within TiO2 that operates at the visible wavelength of λ = 637 nm, the mean fluorescence wavelength of the TiO2 single-photon emitters also presented in this thesis. The electrodynamics of the system was calculated using the finite-difference time-domain method. Preliminary fabrication results were also presented. The trapped light with an optical cavity is routed and connected within an integrated optical circuit using waveguides. An optical waveguide design that exhibits coherent tunnelling adiabatic passage of light was explored. The solving and propagation of optical modes was obtained using a combination of _nite element method and beam propagation method techniques. The design showed robust light transfer despite significant perturbations to the optimised system The archetypal three-waveguide system can be extended to a five-waveguide system where this system acts as a power divider. The three-waveguide system was fabricated into tellurium dioxide, an emerging material for non-linear optical communication applications.