Waveguide discontinuities are frequently encountered in modern photonic structures. It is important to characterize the reflection and transmission that occurs at the discontinuous during the design and analysis process of these structures. Significant effort has been focused upon the development of accurate modelling tools, and a variety of modelling techniques have been applied to solve this kind of problem. Throughout this work, a Transmission matrix based Bidirectional Beam Propagation Method (T-Bi-BPM) is proposed and applied on the uncoated facet and the single coating layer reflection problems, including both normal and angled incident situations. The T-Bi-BPM method is developed on the basis of an overview of Finite Difference Beam Propagation Method (FD-BPM) schemes frequently used in photonic modelling including paraxial FD-BPM, Imaginary Distance (ID) BPM, Wide Angle (WA) BPM and existing Bidirectional (Bi) BPM methods. The T-Bi-BPM establishes the connection between the total fields on either side of the coating layer and the incident field at the input of a single layer coated structure by a matrix system on the basis of a transmission matrix equation used in a transmission line approach. The matrix system can be algebraically preconditioned and then solved by sparse matrix multiplications. The attraction of the T-Bi-BPM method is the potential for more rapid evaluation without iterative approach. The accuracy of the T-Bi-BPM is verified by simulations and the factors that affect the accuracy are investigated.

In optical experiments, replacing the usual constant intensity light source with one that has its intensity modulated at a fixed frequency gives a number of advantages, namely moving the signal of interest away from low frequency noise, allowing the signal to be detected even in the presence of background illumination, as well as being able to gain more information about the experiment by measuring any change in the phase of the modulation. A number of different types of integrating pixels have been simulated in Matlab with regard to their suitability for use as a modulated light detector, along with different methods for reconstructing the signal. The quadrature method of reconstruction was chosen as the best technique, where four samples are taken per modulated time period then all four samples are used in the I and Q channels of the demodulator. A modulated light detector has been implemented using a custom integrated circuit in a standard 0:35 micro m CMOS process, linked to a field programmable gate array. The custom circuits consists of a photodiode configured as an integrating type pixel, where the output of the pixel is connected to a comparator so that when coupled with a counter, the pixel can measure the amount of time taken for the photodiode to reach a particular voltage. A camera with 128 x 128 pixels has been implemented and characterised using a modulated laser as the input, with the results obtained compared to the Matlab simulations carried out. Images have been taken with the camera that show the camera is able to detect modulated light signals at a modulation depth of 1.39% and modulation frequency of 420 Hz. The camera has also been operated successfully for a modulation frequency of 2.5 kHz.

Since the early 1980s the increase in use of pulse oximeters in many clinical situations has been quite remarkable, turning it into one of the most important methods of monitoring in use today. Pulse oximetry essentially uses photoplethysmography to calculate oxygen saturation. Consequently the wavelength dependence of the photoplethysmogram (PPG) is of direct relevance in the performance of pulse oximeters. The experimental results obtained on the wavelength dependence of the AC, DC and AC/DC PPG components for the 450 - 1000nm range are undoubtedly different to the ones predicted by the current simple pulse oximeter model based on the Lambert-Beer law. Moreover, they show unexpected phenomena regarding the magnitude of the above components over the whole range, with distinct differences between the reflection and transmission modes. This is of significance to the technique of pulse oximetry suggesting that perhaps other wavelengths should be considered for use, and that use of both "reflection" and "transmission" probes on the same oximeter may lead to inaccurate readings in one of the modes. A finger model was developed and results from Monte Carlo simulations of photon propagation obtained. The results did not correspond to the experimental results, this is most probably due to either wrong parameters or model. Recent advances in the use of reflection pulse oximeters on fetal monitoring during labour, have raised the question of possible artifacts which may arise due to inadequate probe application in the birth canal. The importance of complete opposition of the reflectance probe was examined on an adult finger. False low oxygen saturation readings were recorded with malpositioned probes. A new probe with modified geometry was designed which offered an improved performance in reducing this artifact and further suggestions were given for its possible elimination. Finally, a proposal for a novel, visible multi-wavelength reflection pulse oximeter is presented with the aim of replacing current pulse oximeters in certain situations where their use is questionable.

The integration of photodetectors with IC circuits provides a significant improvement over conventional designs. Featuring noise reduction, extended frequency responses, lower power consumption, and data operations, these integrated devices open challenging opportunities for many applications. One type of photodetector has the potential for important applications in the life science and remote sensing fields -- a photodetecting device that detects modulated light while rejecting ambient light. A circuit that can reject very bright ambient light yet provide high AC gain for the best signal-to-noise ratio was simulated, constructed and tested by discrete components, and excellent results were obtained. Using 80 klux tungsten light, this device detected an 0.08 lux light signal modulated at 16 kHz, rejecting more than 120 dB of DC light. This circuit was demonstrated by application to a plant physiology study, and the results were also significant. Based on a 1.2 ��m n-well CMOS process, a monolithic device that rejects DC light was designed and simulated by using HSPICE and the SWITCAP2 programs. It was found that a rejection of about 112 dB of DC light may be realized by the CMOS monolithic device. A structure extending this sensor to an imaging device that rejects DC ambient light is also proposed. / Graduation date: 1997

Non-destructive testing is an important field of research in many areas of industry and science. This field covers methods that test some property of an object while not impacting its future usefulness. This project is specifically interested in a method of NDE called Laser Doppler Vibrometry (LDV), which uses light to probe the motion of an object's surface. This thesis presents research into the possibility of developing a full-field LDV camera capable of measuring the vibration at a number of points across an object simultaneously. The approach chosen was to develop a single processing element which contained a light detector as well as the processing required to produce an output signal proportional to the vibration of the surface imaged by the element. This processing element, or pixel, could then be used to produce a full-field LDV camera capable of imaging an object's surface to provide vibration amplitude and frequency for a number of points across the whole surface simultaneously Some early work was carried out measuring the vibration of a piezoelectric target with a CMOS camera and the results were compared with theory. The method of processing chosen is called zero-crossing demodulation and a circuit was designed and simulated using this method. This circuit was then laid-out and a CMOS chip was fabricated with the pixel on it. The circuit was designed such that the different parts of it could be tested separately using electrical signals, and a number of electrical tests were performed to check how well the operation of the fabricated pixel compared with simulation. Using a laser interferometer the pixel was finally tested with real vibrating objects and compared with a commercial LDV.

Modulated Light Cameras represent a breed of cameras designed specifically to capture intensity modulated light. This is because using coherent detection it is possible to lift a signal of interest out of the background noise and thus increase the precision of measurements. This work presents a camera designed to detect the phase of amplitude modulated light. By implementing an in-pixel demodulation, wide-field detection of the phase of light is possible. The camera provides 32 by 32 pixels, each with a pitch of 115 μm with a fill factor of 16 %. This pixel used in the camera introduces a novel tuning mechanism that matches the camera to the frequency of operation and light conditions. This enables the camera to work at high modulation depths, and increases the detection frequency to 50 MHz. The camera also provides an improved linear response without compromising on dynamic range and pixel size. The noise response of the camera is also improved as compared with previous work performed. The camera has been demonstrated in wide-field range measurements of a scene (Imaging LIDAR). It has also been applied to wide-field heterodyne interforemetry and in ultra-stable interferometry.

Optical microresonators can form the basis of all-optical switching and control devices. The presented study is an exploration of the Transmission Line Modelling (TLM) method as a suitable candidate for designing optical microresonators. Chalcogenide glasses were identified as promising materials, with which to fabricate optical microresonators. The study presents the formulation of TLM in two dimensions to model nonmagnetic dielectric materials and a suitable computationally efficient yet flexible software design. Some methods for extracting spectral properties of resonators are compared and the modified difference Prony method was identified as a suitable tool to extract resonant frequencies and Q factors from a limited time signal. When applying TLM to microresonators of sub-wavelength dimensions it was understood that the method of discretisation plays an important role in accurately modelling microresonators. Two novel methods of discretisations -the same area method and the anti-aliasing method- were used to improve the accuracy significantly compared to existing mesh refinement techniques. Perfect matched layers (PMLs) were implemented to improve reflections from domain truncation using several methods. A Convolutional PML(CPML) was identified as the best, but it does not reach the efficiency of PMLs in the Finite Difference Time Domain (FDTD) method. Several frequency dependent refractive index models were proposed and implemented in TLM. A Tauc-Lorentz model was identified as the best fit to the experimental refractive index of three chalcogenide glasses, but a Sellmeier model with one term and a coefficient was efficient for TLM implementation. The main concern in the use of these models within TLM was shown to be the error arising due to mesh dispersion. Kerr nonlinear models were formulated and implemented in TLM and the models applied to the study of a waveguide junction. Compared to an equivalent implementation in a time domain beam propagation method, TLM models better represent the waveguide junction reflections.

The prolific rate at which advances in photonics have been made in recent years has increased the need for accurate and efficient computer aided design tools. New device technologies and material systems mean the designer is faced with many more degrees of freedom with which to optimise a design. Because of this versatile techniques that yield results accurately and quickly are foremost in the designers mind. Throughout this work a well proven technique, the Spectral Index (SI) method is extended and generalised to a wide variety design situations of practical importance. The design of a novel Silicon Germanium based device was used to prove the suitability of an iterative design methodology in developing and optimising practical waveguiding components. The novel development of the SI method for the accurate analysis of waveguide losses is then presented further extending its suitability to the analysis and design of rectangular rib waveguides. Following this the generalisation of the SI method to structures of non-rectangular cross-section is presented allowing for the analysis of a wider range of optical rib waveguides. A novel implementation of the SI method is then developed for the analysis of the whispering gallery class of resonant modes supported by cylindrical dielectric disc and ring structures, allowing for the characterisation of the optical properties of this important class of devices. A 3D circuit analysis technique based upon a robust implementation of the SI method in its complex form is developed that allows for the characterisation of any waveguide system that may be represented by a number of discrete waveguide components. Finally the SI method is generalised to the full 3D exact analysis of optical waveguiding structures.

Photovoltaics are used for the direct conversion of sunlight into electricity. In order to provide useful power, the individual solar cells must be connected together. This electrically connected and environmentally protected unit is termed a photovoltaic (PV) module. The structure of a PV module consists of a number of layers of various materials with different properties. The encapsulation material is one of the critical components of a PV module. It mechanically protects the devices and electrically insulates them, ideally for at least the 20-25 year lifetime of the modules. The lifetime of a PV module is generally limited by the degradation of the constituent parts. The materials degrade and cause a decrease in the efficiency leading to eventual failure, with the encapsulant being particularly susceptible to degradation. The most common encapsulant material is Ethylene Vinyl Acetate (EVA) the degradation of which leads to a significant drop in a PV module’s efficiency, durability and lifetime. EVA undergoes chemical degradation when it is exposed to environmental factors such as elevated temperature, humidity and Ultra Violet (UV) radiation. Although numerous works have been done in this field there is still a gap in knowledge to fully understand the degradation of EVA and develop a predictive tool. This work investigates the chemical degradation of an EVA encapsulant to understand the degradation mechanisms, develop a predictive model and correlate the degradation with changes in the structure and mechanical properties. To determine the effect of environmental stresses on EVA environmental conditions were simulated in the laboratory in order to accelerate the test program. The ageing was classified into three main groups, namely thermal ageing, UV ageing and damp-heat ageing. In order to investigate the effect of elevated temperature on the mechanical and thermal properties and also to study the thermal degradation, EVA sheets were aged in a dark laboratory oven at 85°C for up to 80 days. To investigate the impact of UV exposure on the properties and photodegradation of EVA the samples were exposed to UV radiation of 0.68 W/m2 at 340 nm and 50°C. To study moisture diffusion and the impact of absorbed moisture on the mechanical properties and morphology, EVA sheets were aged in an environmental chamber at 85°C-85% RH and using a potassium chloride (KCl) salt solution in a sealed chamber to obtain 85% RH at room temperature (22±3°C). Thermal analysis techniques including Differential Scanning Calorimetry (DSC), Thermo-gravimetric Analysis (TGA), Dynamic Mechanical Analysis (DMA) along with Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Gravimetrics were used to investigate the structure, degradation kinetics and viscoelastic mechanical properties of the EVA as a function of ageing. The EVA was shown to have viscoelastic properties that were highly sensitive to the ambient temperature. Thermal ageing was shown to reduce the storage modulus due to the changes in the structure of the EVA and reduction in crystallinity. Over a longer time, chemical changes due to thermal activation also occurred, hence, these were insignificant compared with transient thermal effects. The activation energy of deacetylation was also shown not be affected by the ageing process. Investigation of photodegradation showed notable chemical changes as a result of UV exposure, with FTIR absorbance peaks related to carboxylic acid, lactone and vinyl exhibiting a sharp increase after UV irradiation. Differences in the ATR-FTIR spectra of the UV irradiated and non-irradiated samples showed that the intensity is depth dependant. DMA results showed UV ageing had a significant influence on the mechanical properties of the EVA and reduces the storage modulus. The predictive photodegradation model showed a good agreement on the UV irradiated surface with the experimental data where it did not agree well with the results on the non-irradiated side which could be due to the presence of UV absorber. The response of the EVA to damp heat was investigated at two conditions with same the RH level (85% RH) and different temperatures (room temperature and 85°C). The moisture diffusion coefficient was measured via gravimetry and Water Vapour Transmission Rate (WVTR) technique which were well-agreed. Results from DSC indicated that the crystallinity increased due to incorporation of moisture into the structure of the copolymer but decreased as ageing continued, showing the significant influence of elevated temperature and thermal degradation on the structure of EVA. A comparative study of the impact of the ageing on the structure and mechanical properties indicated that UV has a stronger degrading influence comparing to other degradation factors. DSC results also suggested that property changes could be connected to structural modifications. The impact of different degradation factors can be summarised as UV > T > DH.

Capacitive division and other charge-sharing techniques have become ubiquitous within modern technology. Almost all touchscreen devices depend on some form of charge sharing mechanism. The Capacitive-Division Imaging Readout, C-DIR, scheme developed for space/astronomy applications, is a proven concept which has benefited from widespread publication and several iterations of prototyping. In this study, we borrowed this idea and assessed its application in the field of life sciences, specifically, fluorescence lifetime imaging microscopy (FLIM). Firstly, the composite C-DIR camera system was developed using a prototype anode developed by Lapington et al in combination with advanced photomultiplier tube technology developed by Photek Limited, and ultra-fast NINO ASIC and high performance time-to-digital converter, HPTDC, readout electronics developed by CERN. Several issues like signal noise, timing jitter and image distortion required special attention to successfully tune the C-DIR system for obtaining FLIM measurements. The C-DIR was characterized in the context of current detector technologies used for time-resolved applications. The maximum achievable global event rate was determined to be a USB 2.0 hard limit of about 1MHz. The spatial resolution and timing performance were identified as 0.5 line-pairs/mm and 200ps FWHM, respectively, which was comparable to other wide-field fluorescence lifetime cameras. These results provided the basis for using the system in a real situation. Before this was possible, however, it was necessary to engineer a bespoke software platform for data acquisition which could cope with the data rates and reduce raw data emerging from the C-DIR system, producing a format compatible with widely used fitting software. The final stage of the project involved using the C-DIR for real science by reproducing real world experiments which allow for a fitness test of the system in the field. The first experiment involved a calcium calibration where the C-DIR system was calibrated using FLIM on a series of calcium buffers of known concentrations. This C-DIR was able accurately recover the lifetime values from the calcium buffers. The second shorter experiment involved using the calibrated system for the quantification of calcium within living tissue samples using fluorescence lifetime imaging. Results were consistent with those published in the literature which solidified the position of the C-DIR as a viable option for time-resolved fluorescence microscopy.