There is a pressing need to develop alternative communications links due to a number of physical phenomena, limiting the bandwidth and energy efficiency of wire-based systems or economic factors such as cost, material-supply reliability and environmental costs. Networks have moved to optical connections to reduce costs, energy use and to supply high data rates. A primary concern is that current optical-detection devices require high optical power to achieve fast data rates with high signal quality. The energy required therefore, quickly becomes a problem. In this thesis, advances in single-photon avalanche diodes (SPADs) are utilised to reduce the amount of light needed and to reduce the overall energy budget. Current high performance receivers often use exotic materials, many of which have severe environmental impact and have cost, supply and political restrictions. These present a problem when it comes to integration; hence silicon technology is used, allowing small, mass-producible, low power receivers. A reconfigurable SPAD-based integrating receiver in standard 130nm imaging CMOS is presented for links with a readout bandwidth of 100MHz. A maximum count rate of 58G photon/s is observed, with a dynamic range of ≈ 79dB, a sensitivity of ≈ −31.7dBm at 100MHz and a BER of ≈ 1x10−9. We investigate the properties of the receiver for optical communications in the visible spectrum, using its added functionality and reconfigurability to experimentally explore non-ideal influences. The all-digital 32x32 SPAD array, achieves a minimum dead time of 5.9ns, and a median dark count rate (DCR) of 2.5kHz per SPAD. High noise devices can be weighted or removed to optimise the SNR. The power requirements, transient response and received data are explored and limiting factors similar to those of photodiode receivers are observed. The thesis concludes that data can be captured well with such a device but more electrical energy is needed at the receiver due to its fundamental operation. Overall, optical power can be reduced, allowing significant savings in either transmitter power or the transmission length, along with the advantages of an integrated digital chip.

A research report submitted to the Faculty of Health Sciences in fulfilment of the requirements for the degree of Master of Medicine, in Internal Medicine at the University of Witwatersrand, Johannesburg. September 2017 / Differentiating ischaemic left ventricular dysfunction (ILVD) from non-ischaemic left ventricular dysfunction (NILVD) is crucial since appropriately selected patients may benefit from coronary revascularisation. The aim of this study was to evaluate the diagnostic utility of myocardial perfusion imaging (MPI) in patients presenting with left ventricular dysfunction using coronary angiography (CA) as the gold standard. Methods This single centre retrospective study was conducted in 52 patients with heart failure with a reduced ejection fraction (EF< 40%) who had both MPI as well as CA at CHBAH between January 2005 and December 2012. ILVD was diagnosed when the distribution and severity of coronary disease on CA was sufficient to account for the degree of left ventricular dysfunction. Results From a total of 52 patients, 33 (63%) had ILVD and 19 (37%) had NILVD. As compared to patients with NILVD, those with ILVD were more likely to be Indian and White (p=0.0014), have more coronary risk factors (5(2) vs 3(2), p < 0.0001) and more commonly have q waves on the ECG (0% vs 55%, p < 0.0001). MPI had a sensitivity of 100% (95% CI 66-100%) and specificity of 52.63% (95% CI 30.18 - 75.08) for the diagnosis of ILVD. The presence of fixed perfusion defects on MPI was the best predictor of ILVD. Conclusion MPI has high sensitivity but low specificity for the diagnosis of ILVD. This makes it a useful screening test for the exclusion of coronary artery disease in patients presenting with heart failure. / MT2018

In recent years, there has been rapid development in processing of quantum information using quantum states of light. The focus is now turning towards developing real-world implementations of technologies such as all-optical quantum computing and cryptography. The ability to consistently create and control the required single photon states of light is crucial for successful operation. Therefore, high performance single photon sources are very much in demand. The most common approach of generating the required nonclassical states of light is through spontaneous photon pair generation in a nonlinear medium. One photon in the pair is detected to "herald" the presence of the remaining single photon. For many applications the photons are required to be in pure indistinguishable states. However, photon pairs generated in this manner typically suffer from spectral correlations, which can lead to the production of mixed, distinguishable states. Additionally, these sources are probabilistic in nature, which fundamentally limits the number of photons that can be delivered simultaneously by independent sources and hence the scalability of these future technologies. One route to deterministic operation is by actively multiplexing several independent sources together to increase the probability of delivering a single photon from the system. This thesis presents the development and analysis of a multiplexing scheme of heralded single photons in high-purity indistinguishable states within an integrated optical fibre system. The spectral correlations present between the two photons in the pair were minimised by spectrally engineering each photonic crystal fibre source. A novel, in-fibre, broadband filtering scheme was implemented using photonic bandgap fibres. In total, two sources were multiplexed using a fast optical switch, yielding an 86% increase in the heralded count rate from the system.

"Patient motion is a significant cause of artifacts in SPECT imaging. It is important to be able to detect when a patient undergoing SPECT imaging is stationary, and when significant motion has occurred, in order to selectively apply motion compensation. In our system, optical cameras observe reflective markers on the patient. Subsequent image processing determines the marker positions relative to the SPECT system, calculating patient motion. We use this information to decide how to aggregate detected gamma rays (events) into projection images (frames) for tomographic reconstruction. For the most part, patients are stationary, and all events acquired at a single detector angle are treated as a single frame. When a patient moves, it becomes necessary to split a frame into subframes during each of which the patient is stationary. This thesis presents a method for splitting frames based on hypothesis testing. Two competing hypotheses and probability model are designed. Whether to split frames is based on a Bayesian recursive estimation of the likelihood function. The estimation procedure lends itself to an efficient iterative implementation. We show that the frame splitting algorithm performance is good for a sample SNR. Different motion simulation cases are presented to verify the algorithm performance. This work is expected to improve the accuracy of motion compensation in clinical diagnoses."

Time resolved imaging is concerned with the measurement of photon arrival time. It has a wealth of emerging applications including biomedical uses such as fluorescence lifetime microscopy and positron emission tomography, as well as laser ranging and imaging in three dimensions. The impact of time resolved imaging on human life is significant: it can be used to identify cancerous cells in-vivo, how well new drugs may perform, or to guide a robot around a factory or hospital. Two essential building blocks of a time resolved imaging system are a photon detector capable of sensing single photons, and fast time resolvers that can measure the time of flight of light to picosecond resolution. In order to address these emerging applications, miniaturised, single-chip, integrated arrays of photon detectors and time resolvers must be developed with state of the art performance and low cost. The goal of this research is therefore the design, layout and verification of arrays of low noise Single Photon Avalanche Diodes (SPADs) together with high resolution Time-Digital Converters (TDCs) using an advanced silicon fabrication process. The research reported in this Thesis was carried out as part of the E.U. funded Megaframe FP6 Project. A 32x32 pixel, one million frames per second, time correlated imaging device has been designed, simulated and fabricated using a 130nm CMOS Imaging process from ST Microelectronics. The imager array has been implemented together with required support cells in order to transmit data off chip at high speed as well as providing a means of device control, test and calibration. The fabricated imaging device successfully demonstrates the research objectives. The Thesis presents details of design, simulation and characterisation results of the elements of the Megaframe device which were the author’s own work. Highlights of the results include the smallest and lowest noise SPAD devices yet published for this class of fabrication process and an imaging array capable of recording single photon arrivals every microsecond, with a minimum time resolution of fifty picoseconds and single bit linearity.

With data throughput increasing exponentially in wireless communication networks, the limited radio frequency (RF) spectrum is unable to meet the future data rate demand. As a promising complementary approach, optical wireless communication (OWC) has gained significant attention since its licence-free light spectrum provides a considerable amount of communication bandwidth. In conventional OWC systems, the information-carried signal has to be real-valued and non-negative due to the incoherent light output of the conventional optical transmitter, light emitting diode (LED). Therefore, an intensity modulation and direct detection (IM/DD) system is used for establishing the OWC link. Some modified orthogonal frequency division multiplexing (OFDM) schemes have been proposed to achieve suitable optical signals. In previous research, three OFDM-based schemes have been presented, including DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM), asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and unipolar orthogonal frequency division multiplexing (U-OFDM). Basic concepts of SPAD receivers are studied and a novel application in OWC is proposed for a permanent downhole monitoring (PDM) system in the gas and oil industry. In this thesis, a complete model of the SPAD-based OWC system is presented, including some related SPAD metrics, the photon counting process in SPAD and a specific nonlinear distortion caused by passive quenching (PQ) and active quenching (AQ) recharged circuits. Moreover, a practical SPAD-based visible light communication (VLC) system and its theoretical analysis are presented in a long-distance gas pipe with a battery-powered LED and a basic on-off keying (OOK) modulation scheme. In this thesis, two novel optical orthogonal frequency division multiplexing (O-OFDM) technologies are proposed: non-DC-biased orthogonal frequency division multiplexing (NDCOFDM) and OFDM with single-photon avalanche diode (SPAD). The former is designed for optical multiple-input multiple-output (O-MIMO) systems based on the optical spatial modulation (OSM) technique. In NDC-OFDM, signs of modulated O-OFDM symbols and absolute values of the symbols are separately transmitted by different information carrying units. This scheme can eliminate clipping distortion in DCO-OFDM and achieve high power efficiency. Furthermore, as the indices of transmitters carry extra information bits, NDC-OFDM gives a significant improvement in spectral efficiency over ACO-OFDM and U-OFDM. In this thesis, SPAD-based OFDM systems with DCO-OFDM and ACO-OFDM are presented and analysed by considering the nonlinear distortion effect of PQ SPAD and AQ SPAD. A comprehensive digital signal processing of SPAD-based OFDM is shown and theoretical functions of the photon counting distribution in PQ SPAD and AQ SPAD are given. Moreover, based on Bussgang theorem, a conventional method for analysing memoryless distortion, close-formed bit-error rate (BER) expressions of SPAD-based OFDM are derived. Furthermore, SPAD-based OFDM is compared with conventional photo-diode (PD) based OFDM systems, and a gain of 40 dB in power efficiency is observed.

This thesis explores Single-Photon Avalanche Diodes (SPADs), which are solid-state devices for photon timing and counting, and concentrates on SPADs integrated in nano-scale CMOS. The thesis focuses on: the search for new theory regarding Geiger-mode operation; proving the utility of calibrated Technology Computer- Aided Design (TCAD) tools for accurately simulating SPADs for the first time; the investigation of how manufacture influences device operation; and the integration of high performance SPADs into CMOS which rival discrete devices. The accepted theories of SPAD operation are revisited and it is discovered that previously neglected minority carriers have many significant roles such as determining: after-pulsing, Dark Count Rate (DCR), bipolar “SPAD latch-up,” nonequilibrium DCR, and “quenching”. The “quenching” process is revisited and it is concluded that it is the “probability time” of ≈100-200ps, and not the previously thought latching current that is important. SPADs are also found to have transient negative differential resistance. The new theories of SPADs are also supported by steady-state 1D, 2D and 3D TCAD simulations as well as novel transient simulations and videos. It is demonstrated as possible to simulate DCR, Photon Detection Efficiency (PDE), guard ring performance, breakdown voltage, breakdown voltage variation, “quenching,” and transient operation of SPADs with great accuracy. The manufacture of SPADs is studied focusing on the operation and optimisation of guard rings and it is found that ion implantation induced asymmetry from the tilt and rotation/twist is critical. Where symmetric, guard rings fail first along the <100> directions due to enhanced mobility. Process integration rules are outlined for obtaining high performance SPADs in CMOS while maintaining compatibility with transistors. The minimisation of tunnelling with lightly-doped junctions and the reduction of ion implantation induced defects by additional annealing are found essential for achieving low DCR. The thesis demonstrates that it is possible to realise high performance SPADs in CMOS through the innovation of a “Deep SPAD” which achieves record PDE of ≈72% at 560nm with >40% PDE from 410-760nm, combined with 18Hz DCR, <60ps FWHM timing resolution, and <4% after-pulsing which is demonstrated to have potential for significant further improvement. The findings suggest that CMOS SPAD-based micro-systems could outperform existing photon timing and counting solutions in the future.

nÃo hà / Tecnologia da InformaÃÃo QuÃntica à uma Ãrea multidisciplinar nova que tem recebido muita atenÃÃo por ser promissora e devido a seu alto potencial em resolver problemas ainda nÃo solucionados. Dentro desta grande Ãrea, as ComunicaÃÃes QuÃnticas estÃo bastante desenvolvidas. Nesta sub-Ãrea, distribuiÃÃo QuÃntica de Chaves à o campo mais avanÃado. Ela permite que duas partes, chamadas Alice e Bob, compartilhem uma chave criptogrÃfica atravÃs de um canal seguro (seguranÃa garantida por leis da mecÃnica quÃntica). A maior parte dos Sistemas de DistribuiÃÃo QuÃntica de Chaves à executada em enlaces de fibras Ãpticas e, nestes sistemas, a mais importante parte à o Detector de FÃtons Isolados. Detector de FÃtons Isolados à um equipamento capaz de absorver um fÃton e gerar um sinal TTL. Assim, em um Detector de FÃtons Isolados ideal, cada fÃton que chega deve disparar um pulso TTL na saÃda. Dado que a energia de um fÃton isolado à muito baixa, um fotodiodo de avalanche à usado para realizar o processo absorÃÃo do fÃtongeraÃÃo de portador, uma vez que este fotodiodo, se corretamente polarizado, pode disparar uma avalanche de portadores detectÃvel. ApÃs a avalanche ter se iniciado, ela deve ser extinta para evitar qualquer dano ao fotodiodo, o que à feito por um circuito de extinÃÃo de avalanche. O fotodiodo de avalanche à o elemento mais importante de um Detector de FÃtons Isolados e sua caracterizaÃÃo requer muita atenÃÃo. Neste contexto, esta dissertaÃÃo lida com aspectos teÃricos e prÃticos de Detectores de FÃtons Isolados para ComunicaÃÃes QuÃnticas. Inicia com a teoria de fotodiodos de avalanche e circuitos de extinÃÃo (resultados numÃricos de circuitos de extinÃÃo tambÃm sÃo mostrados), e segue atà a caracterizaÃÃo de um Detector de FÃtons Isolados construÃdo em laboratÃrio e suas aplicaÃÃes em metrologia de dispositivos Ãpticos, bem como em resoluÃÃo de nÃmero de fÃtons. / Quantum Information Technology is a new multi-disciplinary area which has received a lot of attention due to its promises and its high potential in solving problems still unsolved. In this big area, Quantum Communication is too much developed. In this subarea, Quantum Key Distribution is the most advanced field. It permits two parties, named Alice and Bob, sharing a cryptography key through a secure channel (guaranteed by laws of quantum mechanics). The most of Quantum Key Distribution Systems run over optical fiber links and, in these systems, the most important part is the Single-Photon Detector. Single-Photon Detector is an equipment able to absorb a photon and generate a TTL pulse. Thus, in an ideal Single-Photon Detector, each photon incoming must trigger a TTL pulse at the output. Since the energy level of a single-photon is too much low, an avalanche photodiode is used to perform the photon absorption-carrier generation process, once this photodiode if correctly biased can trigger a detectable avalanche of carriers. After the avalanche has been started, it must be quenched in order to avoid any damage to the photodiode, which is made by an avalanche quenching circuit. The avalanche photodiode is the most important element of a Single-Photon Detector and its characterization requires much attention. In this context, this dissertation deals with theoretical and practical aspects of Single-Photon Detectors for Quantum Communication. It starts from the theory of avalanche photodiodes and quenching circuits (numerical results of quenching circuits are also shown) and follows until the characterization of a home-made Single-Photon Detector and its applications in Metrology of optical devices and in Photon-Number Resolution as well.

FLIM is branch of microscopy mainly used in biology which is quickly improving thanks to a rapid enhancement of instrumentation and techniques enabled by new sensors. In FLIM, the most precise method of measuring fluorescent decays is called TCSPC. High voltage PMT detection devices together with costly and bulky optical setups which scan the sample are usually required in TCSPC instrumentation. SPADs have enabled a big improvement in TCSPC measurement setup, providing a CMOS compatible device which can be designed in wide arrays format. However, sensors providing in-pixel TCSPC do not scale in size and in large array like the time-gated SPAD pixel sensors do. Time-gated pixels offer a less precise lifetime estimation, discarding any photon information outside a given time window, but this loss in photon-efficiency is offset by gains in pixel size. This work is aimed at the development of a wide field TCSPC sensor with a pixel size and fill factor able to reduce the cost of such devices and to obtain a high resolution time-resolved fluorescence image in the shortest time possible. The study focuses on SPAD and pixel design required to maximise the fill factor in sub 10 μm pixel pitch. Multiple pixel designs are proposed in order to reduce pixel area and so enable affordable wide array TCSPC systems. The first proposed pixel performs the CMM lifetime estimation in order to reduce the frame rate needed to stream the data out of the SPAD array. This pixel is designed in a 10 μm pitch and attains with the most aggressive design a fill factor of 10:17 %. A second design proposes an analogue TCSPC which consists in a S/H TAC circuitry. This simpler pixel can achieve a higher fill factor of 19:63% as well as smaller pitch of 8 μm thanks to the adoption of SPAD n-well and electronics area sharing. This last design is implemented in a 320 x 256 SPAD array in which is included part of a novel ADC aimed at reduction of the processing time required to build a TCSPC histogram. A more conventional analogue readout is used to evaluate the pixel performance as well as a more fine TCSPC histogram. The device was used to measure the fluorescence lifetime of green micro-spheres while the 2b flash ADC is used to demonstrate rapid resolution and separation of two different fluorescence decays.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 143-150).