The conversion from low speed to high speed and vice versa in various forms, including rotary and linear motion, is a requirement for a wide range of applications. For example, wind power generation requires a conversion of low speed rotation of turbine blades to high speed generator rotation, and ocean wave power generation is achievable by conversion of low speed linear motion to either high speed rotation or high speed linear motion. Mechanical gearboxes, hydraulic and pneumatic actuators are commonly used to achieve these conversions. However, these systems suffer from reliability issues, high maintenance requirements, noise, and lack of overload protection. As an alternative, electromagnetic actuators overcome most of the issues related to the mechanical, hydraulic and pneumatic mechanisms. However, magnetic shear stress is constraint by current density and magnetic saturation. Recently, magnetic gearboxes have been proposed, which rely only on magnetic loading. They provide speed and force conversion like their mechanical counterparts, but without thermal constraints (current density limits). Unlike mechanical gears, magnetic gear contact-less operation enables it to operate without lubrication and with low noise, and higher efficiency. Its reliance on magnetic loading also provides overload protection. This dissertation focuses on investigating two new types of magnetic gears; first a magnetically-geared lead screw is proposed, which converts a low speed linear motion to a high speed rotary motion. The proposed actuator is a combination of two previously proposed actuators, the linear magnetic gear and the magnetic lead screw. Unlike these two topologies, the translator part of the proposed magnetically geared lead screw is made entirely of low-cost ferromagnetic steel. Therefore, the translator stroke length can be long without requiring more magnet material. In the second part of this dissertation, an axial flux magnetic gear is proposed that has an integrated outer stator. This axial flux magnetically-geared motor is unique in that the stator shares the high-speed rotor with the magnetic gear, so there is no need for a separate rotor. The high speed and low speed rotors use a flux-focusing typology. The stator is mounted outside the axial flux magnetic gear. This makes the design mechanically less complex. It also enables the stator to be cooled more easily. In the last part of this dissertation, analytical-based models are proposed for a linear permanent magnet coupling and magnetic lead screw. These models help to find the upper bound of the similar devices, which require a scaling analysis. Numerical methods like finite element analysis are accurate and effective enough for modeling various electromechanical and electromagnetic devices. However, these simulations are usually computationally expensive; they require a considerable amount of memory and time, especially when considering 3D finite element simulation. The proposed analytical models offer exact field solution while significantly reducing the computational time. Detailed analysis of two magnetic gears is given under their corresponding chapters. Preliminary experimental results are also provided. The analytical-based model is presented and verified by FEA results. A summary of research contributions and future works is outlined.

This thesis presents results on the applications and limitations of plasma enhanced chemical vapour deposition for silicon-based photonics, with an emphasis on optical microcavities for the control of light emission from silicon nanocrystals. ¶ Silicon nanocrystals were formed by precipitation and growth within Si-rich oxide layers (SiOx) deposited by plasma enhanced chemical vapour deposition. The films were found to exhibit strong room temperature photoluminescence, with the optimum emission depending on the composition and processing of the films. The strongest emission was achieved for films with a silicon content of ~40%, following hydrogen passivation. Hydrogen was introduced into the samples by two different methods: by annealing in forming gas (95% N2: 5% H2) or by annealing with a hydrogenated silicon nitride capping layer. Both methods caused an increase in photoluminescence intensity due to the passivation of defects. In contrast, the presence of low levels of iron and gold were shown to reduce the concentration of luminescent nanocrystals due to the creation of non-radiative centres. ¶ Optical microcavity structures containing silicon nanocrystals were also fabricated by Plasma enhanced chemical vapour deposition, using silicon dioxide, silicon nitride and silicon-rich oxide layers. The microcavities consisted of a silicon-rich oxide layer between two distributed Bragg reflectors formed of alternating silicon dioxide/nitride layers. The optical emission from these and related structures were examined and compared with that from individual layers in the structure. This revealed a complex interplay between defect and nanocrystal luminescence, hydrogen passivation and materials structure. The resulting microcavity structures were shown to be suitable for producing a stop-band over the wavelength range of interest for nanocrystal emission, 500-1000nm, and to produce significant intensity enhancement and spectral narrowing. Quality factors of 50-200 were demonstrated. ¶ The application of plasma deposited films was shown to be limited by stress-induced failure that resulted in cracking and delamination of the films during annealing. The SiOx films thicker than about 600nm failed predominantly by cracking. This was shown to be caused by tensile stress in the film caused by hydrogen desorption during high temperature annealing. The resulting cracks showed preferred alignment depending on the crystallographic orientation of the silicon substrate. For films deposited on (100) silicon, two modes of crack propagation were observed, straight cracks aligned along < 100> directions, and wavy cracks aligned along < 110> directions. For films deposited on (110) silicon, straight cracks were observed along [-1 10] directions, with a lesser number aligned along [001] directions. Cracks were also observed for films on (111) silicon. These showed 3-fold symmetry consistent with crack propagation along < 211> directions due to plastic deformation. Details of these crack geometries and their dependencies are discussed.

Optics and photonics enable important technological solutions for critical areas such as health, communications, energy, and manufacturing. Novel nanofabrication techniques, on the other hand, have enabled the realization of ever shirking devices. On-chip photonic micro-resonators, the fabrication of which was made possible in the recent decade thanks to the progress in nanofabrication, provide a sensitive and scalable transduction mechanism that can be used for biochemical sensing applications. The recognition and quantification of biological molecules is of great interest for a wide range of applications from environmental monitoring and hazard detection to early diagnosis of diseases such as cancer and heart failure. A sensitive and scalable biosensor platform based on an optimized array of silicon nitride microring resonators is proposed for multiplexed, rapid, and label-free detection of biomolecules. The miniature dimension of the proposed sensor allows for the realization of handheld detection devices for limited-resource and point-of-care applications. To realize these sensors, the design, fabrication, stabilization, and integration challenges are addressed. Especially, the focus is placed on solving a major problem in using resonancebased integrated photonic sensors (i.e., the insufficiency of wavelength scan accuracy in typical tunable lasers available) by using an interferometric referencing technique for accurate resonance tracking. This technique can improve the limit of detection of the proposed sensor by more than one order of magnitude. The method does not require any temperature control or cooling, and the biosensor platform does not require narrow linewidths necessary for the biosensors based on ultrahigh quality factor resonators, thus enabling low-cost and reliable integration on the biosensor platform.

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This thesis is about the design, fabrication, and characterization of nanophotonic elements in the visible that can enhance light-matter interaction for single quantum emitters. We focus on two material systems: single photon sources based on the nitrogen-vacancy (NV) center in diamond with improved spontaneous emission rates and collection efficiencies, and passive TiO2 devices that comprise a potentially broadband (from the visible to the infrared), low loss photonics platform and that are suitable for probing and manipulating single colloidal quantum dots. We first discuss the requirements for using color center emission in bulk diamond crystals for potential applications in quantum information processing, and provide examples of using nanowire structures and planar resonators made in diamond for engineering the the NV center’s pump and collection efficiencies, and spontaneous emission rates, respectively. We also describe the integration of diamond with plasmonic structures. We have designed and implemented diamond-silver apertures for broadband enhancements of the spontaneous emission rates of NV centers. We show that shallow-implanted NV centers in diamond nanoposts provide a good system for controlling the NV center spontaneous emission rates, allowing for quenched emission with long lifetimes in the bare case, and enhanced emission with fast decay rates (corresponding to a Purcell factor of around 6) when coated with silver. We add plasmonic gratings around the diamond-silver apertures to improve the collection efficiency of the system, and observe over two-fold improvement in collection. We demonstrate the fabrication of chip-scale linear optical elements such as waveguides and racetrack resonators in low-loss \(TiO_2\) thin films. The fabricated waveguides operate over a wide bandwidth with propagation losses from from 30 dB/cm in the visible to 4 dB/cm in the IR, while racetrack resonators can critically couple to waveg- uides and have quality factors as high as ~22000 in the red wavelengths. We present the fabrication of dielectric slot waveguides and their integration with colloidal quan- tum dots. Finally, we describe efforts to study and control charge transfer processes between quantum dots and \(TiO_2\) on a single emitter level. / Engineering and Applied Sciences

We investigate the properties of integrated dielectric filters for the purposes of on-chip routing of photons. We started with the use of high quality factor tunable photonic crystal nanobeam cavities and moving on to examine a new class of reflection based reverse designed filters that maintain the footprint of a waveguide while allowing for arbitrary amplitude and phase response. / Engineering and Applied Sciences

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.

Thesis (Ph. D.)--School of Physics , Faculty of Science, University of Sydney, 2004. / Bibliography: p. 237-254.

Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, Centre for Micro-Photonics, 2005. / A thesis submitted for the degree of Doctor of Philosophy, Centre for Micro-Photonics, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, 2005. Typescript. Bibliography: p. 129-142.