In this thesis, approaches for increasing the output power in monolithically integrated semiconductor mode locked (ML) lasers were investigated. The wavelength range considered is the range of operation of low temperature grown GaAs photomixers, devices commonly used for THz generation. In particular, two GaAs/AlGaAs quantum well laser epistructures (operating at 830 nm and 795 nm) were considered, both with reduced optical confinement and elongated vertical optical mode size. In this work, such laser epistructures, commonly used by high power semiconductor laser manufacturers, were successfully employed, for the first time, for producing passively ML devices. Improved average powers (up to 48 mW) under ML operation were demonstrated, around ten times higher than values previously reported in monolithic GaAs/AlGaAs ML lasers. In continuous wave operation, the output power was limited by the catastrophic damage of the laser facets at around 50 mW. For this reason, facet passivation techniques were investigated, allowing for powers up to 124 mW to be achieved. In ML regime, the output power was instead limited by the catastrophic damage of the reverse biased section of the laser. This failure mechanism was investigated and explained considering thermal effects on the reverse biased section. Such effects limited the output power to around 27 mW in 830 nm devices, which was then improved by 70% in 795 nm devices with a 70% larger optical mode area. The larger mode size, combined to a small duty-cycle laser geometry, enabled a record peak power of 9.8 W to be achieved at 6.83 GHz. This particular repetition rate was specifically designed for coherent population trapping experiments in 87Rb vapors. Sub-picosecond transform limited pulses were achieved in both the laser materials considered, with a minimum duration of 0.43 ps at 126 GHz. With the values of peak power achieved, the developed devices may also be directly used for two-photon microscopy applications.

Electricity is vital for our daily life in modern cites. In order to ensure its reliability and supply, an electric power monitoring system is indispensable in an electric power system. Currently, most electric power monitoring systems are designed for steady-state monitoring only. They may not be able to monitor instantaneous power disturbances, such as voltage surge, happened in electric power systems. In fact, instantaneous power disturbances are frequently found in electric power systems, which result in equipment failures and cause financial losses. Therefore, a novel electric power monitoring system is proposed in this thesis. Besides traditional functions, the proposed system is capable of monitoring and analyzing instantaneous power disturbances in electric power systems. Novelties of the proposed monitoring system are in the following three major aspects. Firstly, the proposed system is capable of monitoring instantaneous power disturbances. Unlike traditional monitoring systems, the proposed system captures not only statistical power quantities (e.g. kW, kWh), but also voltage and current waveforms. Since a considerable communication network bandwidth is required to transmit electric waveforms in a remote monitoring system, a novel waveform compression algorithm is proposed to realize real-time electric power waveform monitoring on low-speed communication networks (e.g. Zigbee). Secondly, the proposed system is capable of identifying various kinds of power disturbances automatically. It relieves electrical engineers from manned disturbance identification on preserved waveforms. Unlike traditional disturbance identification algorithms, the proposed system can identify not only voltage disturbances, but also current disturbances. Hence, it can provide a better chance in identifying more problems and disturbances in electric power systems. Thirdly, a novel time-frequency analysis method is proposed to analyze preserved waveforms. The proposed method is an improvement to the well-known Discrete Wavelet Packet Transform (DWPT). DWPT has been used by researchers and engineers to analyze disturbances and harmonics in electric power systems. However, DWPT is subjected to a non-uniform leakage problem, which has been discussed intensively in many studies. In order to tackle this issue, a frequency shifting scheme is introduced in the proposed method. A prototype has been implemented to demonstrate the feasibility of the proposed electric power monitoring system. There are two major components – a prototype meter and a central monitoring system. The performance of the prototype has been evaluated by conducting experiments and field tests. The capability of the proposed system for realtime remote monitoring has been verified on Zigbee network, which is a low-power, low speed wireless communication network.

This thesis aims to explore and demonstrate the potential of using optical fibres both as a waveguide material and a transducer for wide sensing applications, based on a comprehensive review of the localised surface plasmon resonance (LSPR) phenomenon, which occurs at a nanoscale level when light interacts with metallic nanoparticles at a resonance wavelength. The LSPR effect of metallic nanomaterials has shown a strong dependence on the local surrounding environment. A small change for example in the refractive index or in the solution concentration can result in a variation in the LSPR spectrum. Based on this underpinning sensing mechanism, a portable system using an optical fibre coated with gold nanoparticles (AuNPs) as a sensing probe has been developed and tested for the refractive index measurement. Coupled with this, a systematic approach has been developed and applied in this work to optimize the performance of the developed system by considering several key factors, such as the size of nanoparticles produced, pH, coating time and coating temperature. The above optimised probes coated with gold-nanoparticles are further cross-compared with those optimized but coated with gold nanorods with a high aspect ratio. Both types of probes are also prepared for a specific biosensing application based on the antibody-antigen interaction to create wavelength-based sensors for the detection of anti-human IgG. Both probes have exhibited excellent refractive index (RI) sensitivity, showing ~914 nm/RIU (refractive index unit) for the probe coated with gold nanoparticles and ~601 nm/RIU for the one coated with gold nanorods. When using the modified probes for the detection of anti-human IgG, both probes are able to achieve a good LOD (limit of detection) at 1.6 nM. Based on the above cross-comparison, further research has been undertaken to explore the potential of nanoparticles of the alloy of gold and silver, with an aim to combine the robustness of gold and the excellent LSPR effect of silver. To do so, various alloy particles with varied gold/silver ratio and sizes have been prepared and tested for their respective refractive index sensitivities. The probe coated with alloy particles with bigger size and higher silver content has shown better performance in RI sensing. The work has shown a clear relationship between the size of alloys, the content ratio of alloys and RI sensitivity. Research has also been undertaken in this thesis to explore the excellent LSPR effect of hollow nanoparticles resulting from the enhanced coupling between the interior and exterior of the hollow particles. Gold hollow nanocages have been successfully synthesised and tested with different hollowness and a LSPR sensor coated with gold nanocages has shown an excellent sensitivity as high as ~1933 nm/RIU, which is more than 3 times higher than that coated with AuNPs. This result has confirmed that a significant improvement in sensitivity can be made possible for further biosensing as well as chemical sensing applications.

This thesis discusses two important designs, analysis and optimization of polarization-based devices such as polarization rotator and splitter. Many optical sub-systems integrate with guided wave photonic devices with two-dimensional confinement and high contrast between the core and cladding. The modes present in such waveguides are not purely of the TE or TM type. They are hybrid in nature, where all six components of the magnetic and electric fields are present. This causes the system fully to be polarization dependent. Currently, the polarization issue is a major topic to be dealt with during the design of high efficiency optoelectronic subsystems for further enhancement of their performances. To characterize the device polarization properties a vectrorial approach is needed. In this work, the numerical analysis has been carried out by using the powerful and versatile full vectorial H-field based finite element method (FEM). This method has been proved to be one of the most accurate numerical methods to date for calculating the modal hybridness, birefringence and consequently to calculate the device length, which is an important parameter when designing devices concerning the polarization issues. Polarization devices may be fabricated by combining several butt-coupled uniform waveguide sections. The Least Squares Boundary Residual (LSBR) method is used to obtain transmission and reflection coefficients of all the polarized modes by considering both the guided and the radiated modes. On the other hand, finite element method cannot calculate the power transfer efficiency directly, hence the LSBR method is used along with the FEM for this purpose. The LSBR method is rigorously convergent, satisfying the boundary conditions in the least square sense over the discontinuity interface. Using this method, the power transfer from the input to the coupler section and at the output ports can be evaluated. When designing polarization rotators, it is necessary to calculate the modal hybridness of a mode. In this research, it is identified that when the symmetric waveguides are broken, the modal hybridity is enhanced, and thereby a high polarization conversion is expected. This work is devoted to the study of design optimization of a compact silicon nanowire polarization device. An interesting and useful comparison is made on their operating properties such as the crosstalk, device length, polarization dependence, and fabrication tolerances of the polarization in directional coupler based devices. In this study initially the H-field modal field profile for a high index contrast silicon nanowire waveguide is shown. The effects of waveguide’s width on the effective indices, hybridness, power confinement in the core, and the cladding have been investigated. The modal birefringence of such silicon nanowire waveguides also is shown. It is presented here that for a silicon nanowire waveguide with height of 220 nm, fundamental and second modes exist in the region of the width being 150 – 300 nm, and 500 – 600 nm, respectively. A compact 52.8 μm long passive polarization rotator (PR) using simple silicon nanowire waveguides is designed with a power transfer of 99 % from input TE to output TM power mode, with cross-talk better than – 20 dB and loss value lower than 0.1 dB. Furthermore, an extensive study of fabrication tolerances of a compact (PR) is undertaken. The design of an ultra-compact polarization splitter (PS) based on silicon-on-insulator (SOI) platform is presented. It is shown here that a low loss, 17.90 μm long compact PS, and wide bandwidth over the entire C-band can be achieved.

Therapeutic ultrasound is a promising treatment method for many common cancers, including prostate cancer. Magnetic resonance image (MRI) guidance of therapeutic ultrasound permits targeting and monitoring of therapy. In this thesis a prototype MRI compatible positioning device for the treatment of prostate cancer using therapeutic ultrasound is presented. The accuracy, MRI compatibility and functionality of the positioning device was evaluated in in vitro experiments (using gel phantoms and in vitro). The MRI was used as the imaging guidance technique. The proposed device incorporates a portable electronic system and operates in two PC controlled stages, linear and angular (X - Θ) and one manual driven stage Z (height of the probe). The device is small and portable and can be placed on the patient’s table to any commercial MRI scanner. The proposed device was tested on two clinical MRI scanners of different manufacturers. Additionally, in this thesis a software that controls an MRI guided focus ultrasound system is presented. The software was written in C sharp and consists of the following options: a) connection with DAQ device, b) tab that controls 2D device, c) tab that controls 3D device, d) tab that controls ultrasound protocol and e) operation command history list, g) MRI compatible camera, h) open and control the DICOM images captured from the MRI scanner during the therapy, i) temperature reading of the HIFU focal point. The proposed positioning device offers approximately 20μm accuracy on linear and angular stages. It incorporates MRI compatible optical encoders as mechanical motion feedback. The accuracy measurements were taken using a digital calibre. The positioning device has range of 111mm in linear stage, ±90o on angular stage and 50mm on Z stage. The design was based on measurements that were taken by a 100 patients. The MRI compatibility and motion accuracy images were taken by scanning gel phantoms using T2W FSE on 1.5T and 3T MRI scanner.

The finite difference time domain (FDTD) method is a popular technique, being used successfully to analyse the electromagnetic properties of many structures, including a range of optical or photonic devices. This method offers several major advantages such as, a minimum level of calculation is required for each of the cells into which the structure is divided, as well as data parallelism and explicit and easy implementation. However, due to the use of the Finite Difference grid, this method suffers from higher numerical dispersion and inaccurate discretisation due to staircasing at slanted and curve edges. The rectangular computational domain in 2D and cuboid computational domain in 3D sometimes makes the method very resource intensive especially for large simulations. Although the finite element (FE) approach is superior for the discretisation of both 2D and 3D structures, most of the FE-based time domain approaches reported so far suffer from limitations due to the implicit or iterative form or the mass matrix formulation, for example. Therefore, the speed of the simulation is much slower than the FDTD method. Time domain analysis of electromagnetic is a very resource intensive numerical technique. Due to the slow performance the FE based techniques are not as popular as the FDTD method. In this research work a new FE based time domain technique has been proposed for both 2D and 3D problems which is similar to the FDTD method explicit and data parallel in nature. The method proposed does not requires any matrix formulation or iteration. It uses minimum possible CPU cycles among any FE-based techniques. The method also utilises a unique meshing scheme to reduce the number of calculation to at least half for 2D and one fifth for 3D compared to any full mesh FE based technique. The method also shows very low numerical dispersion when used with equilateral elements in both 2D and 3D. Thus the proposed method effectively produces results with less numerical dispersion error with lower density mesh compared to the FDTD method. When the advantage in resolution is taken into consideration, calculation of each time-step using the proposed method is significantly faster than the FDTD method.

The aim of this work was to design, fabricate and characterize InP high electron mobility transistor (HEMT) based monolithic millimetre wave integrated circuits (MMIC) which operate at 770Hz. To achieve this active and passive circuit elements were designed, fabricated and characterized and accurate equivalent circuit models extracted. All circuits were designed with coplanar waveguide (CPW) as the transmission medium. Electron beam lithography was used for most fabrication processes in this work. A range of passive elements such as CPW discontinuities, series and parallel MIM and interdigital capacitors of different sizes and NiCr resistors were designed fabricated and measured. Equivalent circuit models of these elements were extracted which were shown to be valid to 110 OHz. Passive circuits such as branch-line coupler, rat-race coupler, Lange coupler and Wilkinson divider were successfully demonstrated at W-band frequencies. In all cases the circuits have equal power splitting characteristics with low insertion losses and very good input and output match over large bandwidth. Equivalent circuits of these circuits were extracted and were used in design of MMICs. Active devices were fabricated on a lattice matched InAIAs/InOaAs InP HEMT material structure. Two different 0.12 f..UD T -gate processes were used to make these devices with a UVIIIIPMMA based process giving superior high frequency performance when compared to a conventional CopolymerlPMMA based T -gate structure. The end to end gate resistance of UVIIIIPMMA T -gate was comparable to the lowest 0.1 J..lm gate resistance ever reported. The HEMTs fabricated in this work have shown fT as high as 1930Hz and MAO of 13 dB at 940Hz. Equivalent circuit models of these HEMTs were extracted and were valid up to 1100Hz. These passive and active circuit models were used to design MMICs, in particular reactively matched single ended, balanced and balanced switching amplifiers at 77 OHz. Direct carrier modulators including BPSK, bi-phase amplitude modulation, QPSK and QAM were designed, fabricated and measured at 770Hz. These modulators are designed with reflection type topology to perform the different modulation schemes. The Balanced BPSK modulator circuit was used to ' .. ~ . demonstrate switching operation· with ON-OFF isolation better than 25 dB. The Pagel Abstract two ON states showed 180±5° phase difference which is almost ideal for BPSK modulation. For all states, the input and output reflections were measured to be better than -17 dB at the design frequency. In the case of QAM and QPSK modulation, the circuits showed non-ideal performance with high insertion loss and phase errors but the input and out put reflections were better than -10 dB.

Recent diversification of the telecommunications industry has resulted in the adaptation of optical materials and their associated fabrication technologies for use in the bioanalytical sensor industry. Flame hydrolysis deposited (FHD) planar silica is one such material. Capable of producing high quality films for optical waveguides, the chemical inertness of the deposited silica makes it an ideal substrate from which to fabricate a biological fluorescence sensor. The aim of the work contained in this thesis was to utilise the FHD silica in optical - fluorescence sensors suitable for use at visible and in particular red wavelengths where several fluorophores can be excited, and background fluorescence from the silica is small. New technologies for producing waveguides have been evaluated in the context of their usefulness in optical sensors, with the intention of producing devices with as few fabrication steps as possible to reduce fabrication time and cost. The design, fabrication and testing of a number of sensor configurations is described, in which optical waveguides were interfaced with microfluidic chambers to provide excitation of a fiuorophore in solution. New waveguide fabrication technologies were used for the first time in sensor systems with integrated microfluidic circuits. Waveguides, written by electron beam densification were evaluated in terms of their performance in splitting an excitation signal into several different components, as would be appropriate for excitation of multiple microfluidic chambers - an 'array sensor'. Both Y-branch waveguides and multimode interference (MMI) splitters were successfully used to split the excitation signal. In addition to electron beam densification, UV irradiation at a wavelength of 157 nm was used to write waveguides in FHD silica. The application of a metal surface mask to define the waveguide structures is described. To allow sensitive detection and identification of fluorophores from FHD silica sensor chips, a single chamber device was successfully interfaced to a system to make time resolved fluorescence measurements, a technique known as time correlated single photon counting (TCSPC). The use of TCSPC allowed measurement of the decay time of the fluorescent dye, by which different fluorescent molecules could be identified, as well as the possibility of low concentration measurements. The research has allowed new technologies for creating waveguides in FHD silica to be adapted for sensing purposes, leading to a platform for creating devices in a number of different configurations.

Smart grid has been advocated in both developing and developed countries in many years to deal with large amount of energy deficit and air pollutions. However, many literatures talked about some specific technologies and implementations, few of them could give a clear picture on the smart grid implementations in a macro scale like what is the main consideration for the smart grid implementations, how to examine the power system operation with communication network deployment, how to determine the optimal technology scheme with consideration of economic and political constraints, and so on. Governments and related institutions are keen to evaluate the cost and benefit of new technologies or mechanisms in a scientific way rather than making decision blindly. Decision Support System, which is an information system based on interactive computers to support decision making in planning, management, operations for evaluating technologies, is an essential tool to provide decision makers with powerful scientific evidence. The objective of the thesis is to identify the data and information processing technologies and mechanisms which will enable the further development of decision support systems that can be used to evaluate the indices for smart grid technology investment in the future. First of all, the thesis introduces the smart grid and its features and technologies in order to clarify the benefits can be obtained from smart grid deployment in many aspects such as economics, environment, reliability, efficiency, security and safety. Besides, it is necessary to understand power system business and operation scenarios which may affect the communication network model. This thesis, for the first time, will give detailed requirements for smart grid simulation according to the power system business and operation. In addition, state of art monitoring system and communication system involved in smart grid for better demand side management will be reviewed in order to find out their impacts reflecting to the power systems. The methods and algorithms applied to the smart grid monitoring, communication technologies for smart grid are summarized and the monitoring systems are compared with each other to see the merits and drawbacks in each type of the monitoring system. In smart grid environment, large number of data are need to be processed and useful information are required to be abstracted for further operation in power systems. Machine learning is a useful tool for data mining and prediction. One of the typical machine learning artificial algorithms, artificial neural network (ANN) for load forecasting in large power system is proposed in this thesis and different learning methods of back-propagation, Quasi-Newton and Levenberg-Marquardt, are compared with each other to seek the best result in load forecasting. Bad load forecasting may leads to demand and generation mismatch, which could cause blackout in power systems. Load shedding schemes are powerful defender for power system from collapsing and keep the grid in integral to a maximum extent. A lesson learned from India blackout in July 2012 is analyzed and recommendations on preventing grid from blackout are given in this work. Also, a new load shedding schemes for an isolated system is proposed in this thesis to take full advantage from information sharing and communication network deployment in smart grid. Lastly, the new trend of decision support system (DSS) for smart grid implementation is summarized and reliability index and stability scenarios for cost benefit analysis are under DSS consideration. Many countries and organizations are setting renewable penetration goals when planning the contribution to reduce the greenhouse gas emission in the future 10 or 20 years. For instance, UK government is expecting to produce 27% of renewable energies EU-wide before 2030. Some simulations have been carried out to demonstrate the physical insight of a power system operation with renewable energy integration and to study the non-dispatchable energy source penetration level. Meanwhile, issues from power system reliability which may affect consumers are required to take into account. Reliability index of Centralized wind generations and that of distributed wind generations are compared with each other under an investment perspective.

Thermoelectric generators (TEGs) convert the thermal energy flowing through them into DC electrical energy in a quantity dependant on the temperature difference across them and the electrical load applied, with a conversion efficiency of typically 5%. Nonetheless, they can be successfully employed to recover energy from waste heat and their use has increased rapidly in recent years, with applications ranging from microwatts to kilowatts, due to energy policy legislations and increasing energy cost determined by climate change, environmental issues and availability of energy sources. The performance of TEGs, subject to thermal and electrical effects, can vary considerably depending on the operating conditions, therefore it is necessary to measure and characterise their performance, and to understand their dynamic behaviour and interaction with the other parts of the system. Based on this knowledge it is then desired to develop an effective electronic system able to control these devices so as to maximise the power generated and increase the overall efficiency of the system. Several TEGs can be electrically connected in series and/or parallel (forming an array) to provide the required voltage and/or current. However, TEGs are usually employed in environments with time-varying temperatures, thermal powers and electrical loads. As a consequence in most TEG systems the individual thermoelectric devices can be subject to temperature mismatch due to operating conditions. Therefore it is of relevant importance to accurately simulate the evolution of thermoelectric systems during thermal and electrical transients. At the same time accurate experimental performance data are necessary to permit precise simulations. Unfortunately, there is still no standardised method to test the electrical and thermal performance of TEGs. This thesis tackles these key challenges and contributes to the pool of existing knowledge about TEGs dealing with four main topics: testing of thermoelectric generators, simulation of thermoelectric generating systems, design and production of power electronic converters for thermoelectric generators, and physical applications of thermoelectric generators. After an introduction to the physical phenomena underlying the operation of TEGs, this thesis describes the innovative test system built at the University of Glasgow to assess the performance of TEG devices in the ”real-world”. The fixture allows a single TEG device to be tested with thermal input power up to 1 kW and hot temperature up to 800◦C with minimal thermal losses and thermal shock; the mechanical clamping force can be adjusted up to 5 kN, and the temperatures are sensed by thermocouples placed directly on the TEGs surfaces. A computer program controls all the instruments in order to minimise errors and to aid accurate measurement and test repeatability. The test rig can measure four TEGs simultaneously, each one individually controlled and heated. This allows testing the performance of TEG arrays under mismatched conditions, e.g., dimensions, clamping force, temperature, etc. Under these circumstances experimental results and a mathematical analysis show that when in operation each TEG in the array will have a different electrical operating point at which maximum energy can be extracted and problems of decreased power output arise. This thesis provides the transient solution to the one-dimensional heat conduction equation with internal heat generation that describes the transfer and generation of heat throughout a thermoelectric device with dynamic exchange of heat through the hot and cold sides. This solution is then included in a model in which the Peltier effect, the thermal masses and the electrical behaviour of the system are also considered. The resulting model is created in Simulink and the comparison with experimental results from a TEG system confirms the accuracy of the simulation tool to predict the evolution of the thermoelectric system both in steady-state and during thermal or electrical transients. This thesis presents an investigation of the optimum electrical operating load to maximise the power produced by a TEG. Both fixed temperature difference and fixed thermal input power conditions are considered. Power electronic converters controlled by a Maximum Power Point Tracking (MPPT) algorithm are used to maximise the power transfer from the TEG to the load. The MPPT method based on the open-circuit voltage is arguably the most suitable for the almost linear electrical characteristic of TEGs. An innovative way to perform the open-circuit voltage measurement during the pseudo-normal operation of the power converter is presented. This MPPT technique is supported by theoretical analysis and used to control an efficient synchronous Buck-Boost converter capable of interfacing TEGs over a wide range of temperatures. The prototype MPPT converter is controlled by an inexpensive microcontroller, and a lead-acid battery is used to accumulate the harvested energy. Experimental results using commercial TEG devices demonstrate the ability of the MPPT converter to accurately track the maximum power point during steady-state and thermal transients. This thesis also presents two practical applications of TEGs. The first application exploits the thermal energy generated by a stove to concurrently produce electrical energy and heat water, while the second application recovers the heat energy rejected to ambient by a car’s exhaust gas system to generate electrical energy for battery charging.