No description available.

This work describes the application of Kinetic Monte Carlo (KMC) modelling technique to organic photovoltaic (OPV) devices. Such devices are an exciting and relatively new form of photovoltaic (PV) technology, which can help bring solar power to the mass market using low energy processing methods, and materials that are cheap, and have several novel characteristics, such as being lightweight, flexible, and potentially even translucent. The modelling technique and many of the results found here are also applicable to other organic devices, such as organic light-emitting displays (OLEDs), as the underlying device physics is very similar. Following an introduction and discussions on the theoretical basis of the work and its computational implementation, the work described in the thesis falls into three main sections: Firstly, an evaluation is performed as to the accuracy of the First Reaction Method (FRM), a means of reducing the computational complexity of KMC simulations. Although this method is widely used, its accuracy when used to model OPV devices has never been satisfactorily evaluated, leading it to be questioned by some authors. Hence, its accuracy under a range of scenarios relevant for OPV simulations was tested and quantified. The findings presented here confirm its validity within the field and disorder ranges that are applicable to OPV device operation, and also give some insight into low-field geminate separation dynamics. Secondly, the KMC methodology, with the FRM approximation, is applied to the investigation of the role of device morphology in determining OPV efficiency. Morphology optimisation has frequently been identified as being key to future device design, and the KMC methodology is unique in its ability to examine this. Furthermore, as the popularity of using self-assembled bicontinuous nanostructures in OPVs grows, it is useful to evaluate their potential impact on OPV efficiency, using the insight gained from investigating morphology in general. Among the main conclusions reached from this work, it was determined that one of the key limiting factors in the efficiency of devices is the angle of the heterojunctions to the field, which is a feature of the device morphology. It was also found that, because of this, bicontinuous structures are unlikely to greatly improve OPV efficiency. Thirdly, modelling was performed in an attempt to reproduce the quantitative experimental characteristics of PFB:F8BT devices. This was achieved through first modelling individual charge mobility in the two polymers in question, and quantifying the effects of different forms of disorder. Having found disorder descriptions that could reproduce the single carrier mobility of both PFB and F8BT, as deduced by Blakesley et. al. using drift-diffusion modelling, this disorder description was applied to single layer devices, in order to deduce the injection barrier. Finally, the disorder and injection barriers deduced were combined with optical modelling to reproduce full photovoltaic behaviour. This was generally found to be successful, and therefore potentially gives some real insight into the nature of polymer disorder, whilst also validating the KMC model used in this thesis. An additional implication of this work is that the KMC model can, in the future, be applied to experimental data which cannot be satisfactorily modelled using drift-diffusion simulations.

The dependence of the optical and structural properties of amorphous and polycrystalline FeSi2 layers fabricated by ion beam sputter deposited (IBSD) FeSi2 and ion beam mixing (IBM), have been characterised. Amorphous and polycrystalline FeSi2 were fabricated using IBSD of Fe and Si at deposition temperatures from room temperature (80 °C) up to 700 °C and post-anneals between 300 and 700 T. Optical absorption measurements revealed direct band gaps for all layers including the amorphous layers from 0.891 - 0.947 eV. Little effect on the optical properties was found for amorphous layers annealed below 500 °C. The band gap value and absorption coefficient only significantly increased upon annealing above 500 °C, coinciding with the transformation from the amorphous to crystalline , B-phase. The deposition temperature was seen to affect the crystallinity of the as-deposited thin films, and vary the optical and structural properties within the layers significantly. An increase in deposition temperature resulted in a decrease of the band gap energies and an increase in photo-absorption by an order of magnitude. Using ion beam mixing, we have demonstrated formation of semiconducting silicides possessing direct band gap energies between 0.89 - 1.43 eV via low energy process conditions on multi-layer structures of Fe - Si. RBS was successfully employed to determine the level of silicidation formed using the extracted depth profiles. Mixing was enhanced upon increasing either the irradiation temperature or the ion fluence. The increase in the silicidation was greater when irradiating similar structures at a higher fluence than at a higher temperature. Optically, the increased silicidation did not affect the band gaps, with values of 0.89 - 1.03 eV upon irradiation of structures with 4- or more layers. Comparison of the effective absorption coefficients a} of structures revealed that although there is higher silicidation within the higher fluence structures, a larger absorption coefficient a was observed for higher temperature mixing. The formation of the FeSi2 at higher temperatures allows the amorphous structure to form with more short-to mid-range order thus exhibiting stronger and sharper absorption.

Free-space optical interconnects (FSOIs) are widely seen as a potential solution to present and future bandwidth bottlenecks for parallel processing applications. This thesis will be focused on the study of a particular FSOI system called Optical Highway (OH). The OH is a polarised beam routing system which uses Polarising Beam Splitters and Liquid Crystals (PBS/LC) assemblies to perform reconfigurable interconnection networks. The properties of the OH make it suitable for implementing different passive static networks. A technology known as Rapid Prototyping (RP) will be employed for the first time in order to create optomechanical structures at low cost and low production times. Off-theshelf optical components will also be characterised in order to implement the OH. Additionally, properties such as reconfigurability, scalability, tolerance to misalignment and polarisation losses will be analysed. The OH will be modelled at three levels: node, optical stage and architecture. Different designs will be proposed and a particular architecture, Optimised Cut-Through Ring (OCTR), will be experimentally implemented. Finally, based on this architecture, a new set of properties will be defined in order to optimise the efficiency of the optical channels.

No description available.

The objective of the work described in this thesis was to optimize the optical phase modulating properties of liquid crystal on silicon (LCoS) devices for non-display applications. This thesis presents the characterization of oxide two deposition processes, modelling of binary phase modulation in ferroelectric liquid crystal SLMs using electronic equivalent circuit, and characterization of multi-phase modulation in nematic liquid crystal with pulse-width modulation. For optimal optical performance of a phase modulating LCoS device, the degree of surface planarisation of the CMOS backplane has to be superior to that of conventional CMOS. Two oxide-deposition processes have been characterized to evaluate their effectiveness in planarising microdisplay backplanes. In order to investigate the trench-filling capabilities of the respective oxide deposition processes, I prepared test samples that had a set of trench patterns (1 - 6 μm wide) etched into 4 μm -thick thermal oxide on a Si-substrate. I found that the trench filling capability of an electron cyclotron resonance chemical vapor deposition (ECR CVD) process is superior to that of a pyrolytic CVD process. I investigated the effects of ECR CVD deposition parameters on trench-filling properties and demonstrated the ability to produce deposited oxide layers which fill high aspect ratio trenches without producing voids. Modelling of binary phase modulation is required for optimal performance of ferroelectric liquid crystals on silicon SLMs when used in coherent optical systems. This thesis presents a modelling technique by which an HSpice model can be provided for characterization of phase modulation properties for designing FLC-on-silicon SLMs. The simulation and experimental measurements of phase modulation are described. For the theoretical model simulation, FLC parameter measurements are described. I experimentally verified the modeled prediction of phase modulation by investigating reflective FLC test cells. I have shown reasonable agreement within 9 % between the measured and simulated values of phase modulation. In phase modulating diffractive optical devices multi-phase modulation provides improved performance over binary modulation. Multi-phase modulation can be achieved by using nematic liquid crystal spatial light modulators (NLCSLM) with pulse-width modulation driven from a binary CMOS backplane. This thesis presents the characteristics and the driving scheme of the 512x512 Si-backplane SLM for the implementation of the multi-phase modulation while comparing the binary and four-level phase holograms. A diffraction efficiency of 39.7% for binary grating and 72.7% for four-level blazed grating were obtained at a spatial frequency of 0.78 lines per mm.

This thesis concerns the development of novel resolution-enhancing optical techniques for the purposes of non-destructive sub-surface semiconductor integrated-circuit (IC) inspection. This was achieved by utilising solid immersion lens (SIL) technology, polarisation-dependent imaging, pupil-function engineering and optical coherence tomography (OCT). A SIL-enhanced two-photon optical beam induced current (TOBIC) microscope was constructed for the acquisition of ultra-high-resolution two- and three-dimensional images of a silicon flip-chip using a 1.55μm modelocked Er:fibre laser. This technology provided diffraction-limited lateral and axial resolutions of 166nm and 100nm, respectively - an order of magnitude improvement over previous TOBIC imaging work. The ultra-high numerical aperture (NA) provided by SIL-imaging in silicon (NA=3.5) was used to show, for the first time, the presence of polarisation-dependent vectorialfield effects in an image. These effects were modelled using vector diffraction theory to confirm the increasing ellipticity of the focal-plane energy density distribution as the NA of the system approaches unity. An unprecedented resolution performance ranging from 240nm to ~100nm was obtained, depending of the state of polarisation used. The resolution-enhancing effects of pupil-function engineering were investigated and implemented into a nonlinear polarisation-dependent SIL-enhanced laser microscope to demonstrate a minimum resolution performance of 70nm in a silicon flip-chip. The performance of the annular apertures used in this work was modelled using vectorial diffraction theory to interpret the experimentally-obtained images. The development of an ultra-high-resolution high-dynamic-range OCT system is reported which utilised a broadband supercontinuum source and a balanced-detection scheme in a time-domain Michelson interferometer to achieve an axial resolution of 2.5μm (in air). The examination of silicon ICs demonstrated both a unique substrate profiling and novel inspection technology for circuit navigation and characterisation. In addition, the application of OCT to the investigation of artwork samples and contemporary banknotes is demonstrated for the purposes of art conservation and counterfeit prevention.

This thesis studies optoelectronic devices and the integration of these components onto optoelectronic multi chip modules (OE-MCMs) using a combination of packaging techniques. For this project, (1×12) array photodetectors were developed using PIN diodes with a GaAs/AlGaAs strained layer structure. The devices had a pitch of 250μm, operated at a wavelength of 850nm. Optical characterisation experiments of two types of detector arrays (shoe and ring) were successfully performed. Overall, the shoe devices achieved more consistent results in comparison with ring diodes, i.e. lower dark current and series resistance values. A decision was made to choose the shoe design for implementation into the high speed systems demonstrator. The (1x12) VCSEL array devices were the optical sources used in my research. This was an identical array at 250μm pitch configuration used in order to match the photodetector array. These devices had a wavelength of 850nm. Optoelectronic testing of the VCSEL was successfully conducted, which provided good beam profile analysis and I-V-P measurements of the VCSEL array. This was then implemented into a simple demonstrator system, where eye diagrams examined the systems performance and characteristics of the full system and showed positive results. An explanation was given of the following optoelectronic bonding techniques: Wire bonding and flip chip bonding with its associated technologies, i.e. Solder, gold stud bump and ACF. Also, technologies, such as ultrasonic flip chip bonding and gold micro-post technology were looked into and discussed. Experimental work implementing these methods on packaging the optoelectronic devices was successfully conducted and described in detail. Packaging of the optoelectronic devices onto the OEMCM was successfully performed. Electrical tests were successfully carried out on the flip chip bonded VCSEL and Photodetector arrays. These results verified that the devices attached on the MCM achieved good electrical performance and reliable bonding. Finally, preliminary testing was conducted on the fully assembled OE-MCMs. The aim was to initially power up the mixed signal chip (VCSEL driver), and then observe the VCSEL output.

The work within this thesis investigates the characteristics and sensing properties of novel near- and mid-infrared tellurite and germanate glass fibres and their potential as sensing elements. An asymmetric splicing method for fusion-splicing tellurite and germanate glass fibres to standard silica fibre is demonstrated. The thermal and strain sensing properties of these glass fibres have been studied by analysing the properties of optical fibre Fabry-Perot cavities, which were formed when these high refractive index fibres were spliced to silica fibre, and fibre Bragg gratings. Using fibre F-P interferometer, the normalized thermal sensitivity of tellurite and germanate fibre was measured to be 10.76×10-6/°C and 15.56×10-6/°C respectively, and the normalized strain sensitivity of tellurite and germanate fibre was also measured with values of 0.676×10-6 /με and 0.817×10-6 /με respectively. These results show good agreement with measurements using fibre Bragg gratings in these fibres and are reasonably consistent with the values predicted using available published data for glasses of similar compositions. Tellurite and germanate glass fibres show potential as thermal sensing and load sensing elements compared with silica fibre. The design of an evanescent field gas sensor using tapered germanate fibre for methane gas species detection was investigated and modelled. This model shows the maximum gas cell length (sensing fibre length), detectable gas concentration range, and required gas cell length range for the expected minimum detectable gas concentration of a fibre evanescent field sensor, which gives guidance for the effective gas cell length choosen according to different minimum detectable gas concentration requirement in practise. The investigation of tellurite and germanate glass fibre characteristics and sensing properties offer guidance for their applications in sensing areas.

work presented in this thesis encompasses an investigation into the use of ultrafast laser inscription in the fabrication of glass based photonic devices for integrated optical applications. Waveguide fabrication and characterisation experiments were carried out in three categories of glass substrate. Firstly, waveguides were inscribed in an erbium doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.5 μm spectral region. Low loss waveguides were fabricated in substrates with different dopant concentrations. Fibre to fibre net gain was achieved from one substrate composition, however it was found that ion clustering limited the amount of achievable gain. Laser action was demonstrated by constructing an optical fibre based cavity around the erbium doped waveguide amplifier. Waveguides were also inscribed in bismuth doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.3 μm spectral region. Low loss waveguides were fabricated, however the initial composition was incapable of providing gain. A proven substrate material was employed, demonstrating ultra-broadband gain spanning more than 250 nm. High losses prevented the achievement of net gain, however the broad potential of the substrate material was highlighted. Finally, waveguides were inscribed in a Chalcogenide glass. Strong refractive index contrasts were observed, with a wide range of waveguiding structures produced. Supercontinuum experiments were carried out in order to confirm the nonlinear behaviour of the waveguides. A spectrally smooth supercontinuum spanning 600 nm was generated, providing a potentially useful source for optical coherence tomography.