Working with nanoscale optics requires methods and equipment designed for the purpose. This thesis describes the development of techniques and a system for performing highly localised spectroscopy. The system consists of a nanonics multiview 2000 scanning near-field optical microscope, a grating spectrometer and a photonic crystal fibre supercontinuum light source. Discussion of the microscope includes its modes of operation and development of software to collect and analyse data. In order to demonstrate the setup, an example of localised spectroscopy is presented in the form of an investigation of hollow core photonic crystal fibre. Taking spectra of the components of the cladding of these fibres makes it possible to investigate the origins of bandgap guidance. A core focus of nanoscale optics is the interaction of light with metal structures. This field is called plasmonics. Fabrication of structures is presented and requires special facilities and processes. These processes are both time consuming and expensive, both factors that emphasise the need for prior modelling. Forward difference time domain modelling of a proposed structure comprising of a concentrically arranged ring and disk is explored using home written code and a commercial package called CST Microwave Studio. The investigation of this concentric design through modelling shows a very highly localised field enhancement which can be engineered to have a narrow spectral resonance in the near infrared. The interaction of the two components which govern this resonance is explained using a theory called plasmon hybridization. Once the optical behaviour of small metal objects is understood they can be used in other ways. An example of this is shown in Porous Silicon. As a material it provides an excellent template for formation of metal nano-particles. Embedded in a high surface area network of silicon these particles can be used as very effcient catalysts.

Este trabalho teve como objetivo principal a fabricação de fotodetetores do tipo Metal-Semicondutor-Metal (MSM) com corrente de escuro da ordem de 1 nA, responsividade da ordem de 0,1 A/W e razão fotocorrente/corrente de escuro de pelo menos 10. Estes valores asseguram que os fotodetetores obtidos tenham sensibilidade suficiente para serem utilizados em sensores ópticos integrados. Todos os materiais utilizados na construção dos fotodetetores MSM são compatíveis com processos convencionais de fabricação em microeletrônica, facilitando a integração com outros dispositivos em estado sólido. O semicondutor utilizado nos fotodetetores foi o silício, na forma monocristalina ou policristalina. Como material de eletrodo, foi utilizado o alumínio, o titânio ou o níquel. No processo de fabricação básico, foram utilizados apenas três etapas: deposição do filme metálico, fotolitografia e corrosão, confirmando a simplicidade de fabricação desse fotodetetor. Através da construção de dispositivos com diferentes geometrias e diferentes combinações dos materiais citados acima, foi possível verificar a influência que a estrutura cristalina do semicondutor, tipo de dopagem do semicondutor, geometria e material de eletrodo tem sobre o desempenho e o comportamento dos MSMs. O comprimento de onda de 632,8 nm foi utilizado na caracterização dos dispositivos, devido a sua disponibilidade e o desenvolvimento de guias ópticos utilizando esse comprimento de onda em trabalhos anteriores do nosso grupo de pesquisa. Os melhores resultados obtidos foram com as amostras de Si monocristalino tipo-p com eletrodos de titânio. Na amostra sinterizada à 250°C foi obtido um valor da corrente de escuro de 4,8 nA e, na amostra de referência, foi obtido um valor de responsividade de 0,28 A/W. / The goal of this work was the fabrication of Metal-Semiconductor-Metal (MSM) photodetectors with the following characteristics: dark current of about 1 nA, responsivity of about 0.1 A/W and dark/photocurrent ratio of at least 10. These values ensure that the photodetectors have enough sensitivity to be used in integrated optic sensors. All materials used in the fabrication of the MSM are compatible with conventional microelectronic manufacture process, so that the photodetectors can be more easily integrated with other solid-state devices. The semiconductor used in the photodetectors was silicon, in single crystal and polycrystalline form. As material of electrodes, aluminum, titanium or nickel had been used. The basic fabrication process consists of only three steps: metal film deposition, photolithography and etching, which confirm the simplicity of the fabrication of this device. Building MSMs with different geometries and making combinations with the materials cited above, gave the possibility to verify the influence that crystalline structure of the semiconductor, doping type of the semiconductor, geometry and electrode material have on the behavior of the photodetectors. The wavelength of 632.8 nm was used in the characterization of the devices, due to its availability and the development of optic waveguides using this wavelength in previous works of our research group. The best results were obtained with the samples fabricated using single crystal Si p-type with titanium electrodes. The sample annealed at 250°C had dark current value of 4.8 nA and, the reference sample had responsivity of 0.28 A/W.

Malignant or benign tumors may be ablated with high‐intensity focused ultrasound (HIFU). This technique, known as focused ultrasound surgery (FUS), has been actively investigated for decades, but slow to be implemented and difficult to control due to lack of real‐time feedback during ablation. Two methods of imaging and monitoring HIFU lesions during formation were implemented simultaneously, in order to investigate the efficacy of each and to increase confidence in the detection of the lesion. The first, Acousto‐Optic Imaging (AOI) detects the increasing optical absorption and scattering in the lesion. The intensity of a diffuse optical field in illuminated tissue is mapped at the spatial resolution of an ultrasound focal spot, using the acousto‐optic effect. The second, Harmonic Motion Imaging (HMI), detects the changing stiffness in the lesion. The HIFU beam is modulated to force oscillatory motion in the tissue, and the amplitude of this motion, measured by ultrasound pulse‐echo techniques, is influenced by the stiffness. Experiments were performed on store‐bought chicken breast and freshly slaughtered bovine liver. The AOI results correlated with the onset and relative size of forming lesions much better than prior knowledge of the HIFU power and duration. For HMI, a significant artifact was discovered due to acoustic nonlinearity. The artifact was mitigated by adjusting the phase of the HIFU and imaging pulses. A more detailed model of the HMI process than previously published was made using finite element analysis. The model showed that the amplitude of harmonic motion was primarily affected by increases in acoustic attenuation and stiffness as the lesion formed and the interaction of these effects was complex and often counteracted each other. Further biological variability in tissue properties meant that changes in motion were masked by sample‐to‐sample variation. The HMI experiments predicted lesion formation in only about a quarter of the lesions made. In simultaneous AOI/HMI experiments it appeared that AOI was a more robust method for lesion detection. / Bernard M. Gordon Center for Subsurface and Imaging Systems (CenSSIS) via the NSF ERC award number EEC‐9986821.

Kong Fung Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 59-70). / Chapter CHATPER 1 --- GENERAL INTRODUCTION --- p.1-12 / Chapter CHATPER 2 --- EXAMINATION OF THE BEHAVIOR OF GROWTH CONE IN DIFFERENT REGIONS OF THE OPTIC CHIASM / Introduction --- p.13-14 / Materials and Methods --- p.15-18 / Results --- p.19-23 / Discussion --- p.24-27 / Chapter CHATPER 3 --- STUDY OF BINOCULAR INTERACTION AFTER UNILATERAL INTRA-UTERO ENUCLEATION / Introduction --- p.28-29 / Materials and Methods --- p.30-31 / Results --- p.32-35 / Discussion --- p.36-39 / Chapter CHATPER 4 --- ISOLATION OF DIFFERENTIALLY EXPRESSED mRNA IN DIFFERENT REGIONS OF THE RETINA / Introduction --- p.40-43 / Materials and Methods --- p.44-48 / Results --- p.48-50 / Discussion --- p.51-54 / Chapter CHATPER 5 --- GENERAL DISCUSSION --- p.56-58 / REFERENCE --- p.59-70 / FIGURES / TABLES

Biosensor development has the potential to meet the need for rapid, sensitive, and specific detection of pathogenic bacteria from natural sources. An antibody-based fiber-optic biosensor assay to detect low levels of Vibrio vulnificus in estuarine waters following an enrichment step was developed. The principle of the sensor is based on an immuno-sandwich assay where an anti-V. vulnificus polyclonal capture antibody preparation was first immobilized on a polystyrene fiber-optic waveguide using a biotin-avidin association. The capture antibody is responsible for binding the target cells to the waveguide. Cyanine-5-conjugated anti-V. vulnificus polyclonal antibodies are subsequently allowed to bind to immobilized cells, and detection occurs when a photodetector collects emitted light (670-710 nm) from the fluorophore, which is excited with 635-nm laser light produced by the Analyte 2000 biosensor. Any detection signal greater than a pre-determined threshold signal is considered to be a positive detection event, while any signal lower than the threshold is considered no detection. This immunosensor assay proved highly specific when tested against whole cells and cell extracts from V. cholerae, V. parahaemolyticus, V. alginolyticus, and E. coli. isolates. Following a four hour enrichment in PNCC broth, and in a total of less than seven hours, the assay was able to detect cell extracts from as few as 100 V. vulnificus colony forming units suspended in sterile water. This method holds promise for detection of low numbers V. vulnificus and other autochthonous pathogens in estuarine waters.

Abstract not available

In this thesis, my main focus was to establish a novel composite-cavity fibre laser (CCFL) and to apply it in sensing, particularly in the hydrophone application. The CCFL that I have proposed is formed by writing three wavelength matched fibre Bragg gratings directly into a continuous length of doped fibre. I have also examined the relative advantages and disadvantages of interferometric and intensity-based hydrophone systems, and have established a hydrophone system that can be switched between the two modes of operation, by making use of digital signal processing. I have established a theoretical model to study the lasing and spectral characteristics of the CCFL. My analysis showed that whilst the CCFL have significantly different phase and threshold conditions from the common semiconductor diode lasers with external cavity, the CCFL also have mode-limiting properties that are often sought after. Through simulations, I was able to identify that a non-uniform straining scheme, that is, when one of the sub-cavities of the CCFL is restrained from strain, can improve the sensitivity with respect to existing single cavity fibre lasers, in both the frequency and intensity domains. My simulations also showed that the sensitivity of such a straining scheme can be optimised by tuning the reflectivity of the gratings, sub-cavity lengths, doping concentration and pump power. I have fabricated multiple CCFLs using the in-house grating writing facilities, and have experimentally assessed their power and spectral related lasing characteristics. Whilst having a significantly longer total cavity length compared to typical fibre lasers, the CCFLs demonstrated stable single longitudinal mode operation and narrow linewidth in the order for a few tens of kHz. Asymmetric output power and frequency as a result of unequal sub-cavity lengths were also examined. Finally, I conducted sensing experiments by applying the CCFLs in strain monitoring and intensity-based hydrophone. My results showed that the non-uniform straining scheme had significantly improved the intensity response of the CCFL, and that the acoustic pressure and frequency can be determined by directly sampling and applying Fourier transform to the output intensity of the fibre laser.

This thesis makes a number of new contributions to control and sensing for unmanned vehicles. I begin by developing a non-linear simulation of a small unmanned helicopter and then proceed to develop new algorithms for control and sensing using the simulation. The work is field-tested in successful flight trials of biologically inspired vision and neural network control for an unstable rotorcraft. The techniques are more robust and more easily implemented on a small flying vehicle than previously attempted methods.¶ Experiments from biology suggest that the sensing of image motion or optic flow in insects provides a means of determining the range to obstacles and terrain. This biologically inspired approach is applied to control of height in a helicopter, leading to the World’s first optic flow based terrain following controller for an unmanned helicopter in forward flight. Another novel optic flow based controller is developed for the control of velocity in hover. Using the measurements of height from other sensors, optic flow is used to provide a measure of the helicopters lateral and longitudinal velocities relative to the ground plane. Feedback of these velocity measurements enables automated hover with a drift of only a few cm per second, which is sufficient to allow a helicopter to land autonomously in gusty conditions with no absolute measurement of position.¶ New techniques for sensor fusion using Extended Kalman Filtering are developed to estimate attitude and velocity from noisy inertial sensors and optic flow measurements. However, such control and sensor fusion techniques can be computationally intensive, rendering them difficult or impossible to implement on a small unmanned vehicle due to limitations on computing resources. Since neural networks can perform these functions with minimal computing hardware, a new technique of control using neural networks is presented. First a hybrid plant model consisting of exactly known dynamics is combined with a black-box representation of the unknown dynamics. Simulated trajectories are then calculated for the plant using an optimal controller. Finally, a neural network is trained to mimic the optimal controller. Flight test results of control of the heave dynamics of a helicopter confirm the neural network controller’s ability to operate in high disturbance conditions and suggest that the neural network outperforms a PD controller. Sensor fusion and control of the lateral and longitudinal dynamics of the helicopter are also shown to be easily achieved using computationally modest neural networks.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.