Single-photon avalanche diodes (SPADs) capable of single photon detection are promising optical sensors for use as receivers in optical wireless communication (OWC) systems. In SPAD-based receivers, the intersymbol interference (ISI) effect caused by dead time is an important drawback that limits performance. In this thesis, we propose two novel SPAD operation receivers to reduce the ISI effect in SPAD-based OWC. To validate the feasibility of these two modes, we design a free-running SPAD front-end circuit with post-layout transient simulation results. This SPAD circuit is improved by a novel mixed passive-active quench and reset front-end circuit that achieves a very short dead time. Based on the traditional free-running mode, we design the clock-driven mode and time-gated mode to reduce the ISI effect through time-controlled operating signals. In this work, we develop a new simulation system to assess the ISI effect in On-Off Keying (OOK) modulated communication and pulse position modulated (PPM) communication. To accurately evaluate these three modes, we build a OWC platform to test our proposed SPAD receiver manufactured by TSMC 65 nm process. The Test results demonstrate that the clock-driven mode and time-gated mode receivers can improve the bit error rate (BER) performance in low data rate communication and high data rate high optical power communication, respectively. Moreover, compared to the free-running mode, the two proposed time-controlled modes achieve higher data rate communication and better noise tolerance ability in SPAD-based OWC. / Thesis / Master of Applied Science (MASc) / Optical communication involves using light as a signal to transmit information, and it is currently a highly popular field of research. However, optical receivers used in this type of communication often require specific conditions, which can limit the overall performance of the communication system. To address this issue, we have developed an optical sensor tailored for optical communication. This sensor boasts exceptional sensitivity, allowing it to detect individual particles of light, thereby substantially reducing the demand for signal intensity in the optical communication system. Moreover, we have devised three operational circuits that enhance the sensor's responsiveness to signals under specific communication conditions. We have created a mathematical model to evaluate the proposed optical sensor and the designed circuits, and subsequently manufactured the optical sensor. Both the simulation results and the actual test outcomes unequivocally demonstrate that our proposed sensor has the potential to enhance the performance of optical communication systems.

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.

Fluorescence based analysis is a fundamental research technique used in the life sciences. However, conventional fluorescence intensity measurements are prone to misinterpretation due to illumination and fluorophore concentration non-uniformities. Thus, there is a growing interest in time-resolved fluorescence detection, whereby the characteristic fluorescence decay time-constant (or lifetime) in response to an impulse excitation source is measured. The sensitivity of a sample’s lifetime properties to the micro-environment provides an extremely powerful analysis tool. However, current fluorescence lifetime analysis equipment tends to be bulky, delicate and expensive, thereby restricting its use to research laboratories. Progress in miniaturisation of biological and chemical analysis instrumentation is creating low-cost, robust and portable diagnostic tools capable of high-throughput, with reduced reagent quantities and analysis times. Such devices will enable point-of-care or in-the-field diagnostics. It was the ultimate aim of this project to produce an integrated fluorescence lifetime analysis system capable of sub-nano second precision with an instrument measuring less than 1cm3, something hitherto impossible with existing approaches. To accomplish this, advances in the development of AlInGaN micro-LEDs and high sensitivity CMOS detectors have been exploited. CMOS allows electronic circuitry to be integrated alongside the photodetectors and LED drivers to produce a highly integrated system capable of processing detector data directly without the need for additional external hardware. In this work, a 16x4 array of single-photon avalanche diodes (SPADs) integrated in a 0.35μm high-voltage CMOS technology has been implemented which incorporates two 9-bit, in-pixel time-gated counter circuits, with a resolution of 400ps and on-chip timing generation, in order to directly process fluorescence decay data. The SPAD detector can accurately capture fluorescence lifetime data for samples with concentrations down to 10nM, demonstrated using colloidal quantum dot and conventional fluorophores. The lifetimes captured using the on-chip time gated counters are shown to be equivalent to those processed using commercially available external time-correlated single-photon counting (TCSPC) hardware. A compact excitation source, capable of producing sub-nano second optical pulses, was designed using AlInGaN micro-LEDs bump-bonded to a CMOS driver backplane. A series of driver array designs are presented which are electrically contacted to an equivalent array of micro-LEDs emitting at a wavelength of 370nm. The final micro-LED driver design is capable of producing optical pulses of 300ps in width (full width half maximum, FWHM) and a maximum DC optical output power of 550μW, this is, to the best of our knowledge, the shortest reported optical pulse from a CMOS driven micro-LED device. By integrating an array of CMOS SPAD detectors and an array of CMOS driven AlInGaN micro-LEDs, a complete micro-system for time-resolved fluorescence analysis has been realised. Two different system configurations are evaluated and the ability of both topologies to accurately capture lifetime data is demonstrated. By making use of standard CMOS foundry technologies, this work opens up the possibility of a low-cost, portable chemical/bio-diagnostic device. These first-generation prototypes described herein demonstrate the first time-resolved fluorescence lifetime analysis using an integrated micro-system approach. A number of possible design improvements have been identified which could significantly enhance future device performance resulting in increased detector and micro-LED array density, improved time-gate resolution, shorter excitation pulse widths with increased optical output power and improved excitation light filtering. The integration of sample handling elements has also been proposed, allowing the sample of interest to be accurately manipulated within the micro-environment during investigation.

Vision has always been one of the most important cognitive tools of human beings. In this regard, the development of image sensors opens up the potential to view objects that our eyes cannot see. One of the most promising capability in some image sensors is their single-photon sensitivity that provides information at the ultimate fundamental limit of light. Time-resolved single-photon avalanche diode (SPAD) image sensors bring a new dimension as they measure the arrival time of incident photons with a precision in the order of hundred picoseconds. In addition to this characteristic, they can be fabricated in complementary metal-oxide-semiconductor (CMOS) technology enabling the integration of complex signal processing blocks at the pixel level. These unique features made CMOS SPAD sensors a prime candidate for a broad spectrum of applications. This thesis is dedicated to the optimization and characterization of quantum imagers based on the SPADs as part of the E.U. funded SUPERTWIN project to surpass the fundamental diffraction limit known as the Rayleigh limit by exploiting the spatio-temporal correlation of entangled photons. The first characterized sensor is a 32×32-pixel SPAD array, named “SuperEllen”, with in-pixel time-to-digital converters (TDC) that measure the spatial cross-correlation functions of a flux of entangled photons. Each pixel features 19.48% fill-factor (FF) in 44.64-μm pitch fabricated in a 150-nm CMOS standard technology. The sensor is fully characterized in several electro-optical experiments, in order to be used in quantum imaging measurements. Moreover, the chip is calibrated in terms of coincidence detection achieving the minimal coincidence window determined by the SPAD jitter. The second developed sensor in the context of SUPERTWIN project is a 224×272-pixel SPAD-based array called “SuperAlice”, a multi-functional image sensor fabricated in a 110-nm CMOS image sensor technology. SuperAlice can operate in multiple modes (time-resolving or photon counting or binary imaging mode). Thanks to the digital intrinsic nature of SPAD imagers, they have an inherent capability to achieve a high frame rate. However, running at high frame rate means high I/O power consumption and thus inefficient handling of the generated data, as SPAD arrays are employed for low light applications in which data are very sparse over time and space. Here, we present three zero-suppression mechanisms to increase the frame rate without adversely affecting power consumption. A row-skipping mechanism that is implemented in both SuperEllen and SuperAlice detects the absence of SPAD activity in a row to increase the duty cycle. A current-based mechanism implemented in SuperEllen ignores reading out a full frame when the number of triggered pixels is less than a user-defined value. A different zero-suppression technique is developed in the SuperAlice chip that is based on jumping through the non-zero pixels within one row. The acquisition of TDC-based SPAD imagers can be speeded up further by storing and processing events inside the chip without the need to read out all data. An on-chip histogramming architecture based on analog counters is developed in a 150-nm CMOS standard technology. The test structure is a 16-bin histogram with 9 bit depth for each bin. SPAD technology demonstrates its capability in other applications such as automotive that demands high dynamic range (HDR) imaging. We proposed two methods based on processing photon arrival times to create HDR images. The proposed methods are validated experimentally with SuperEllen obtaining >130 dB dynamic range within 30 ms of integration time and can be further extended by using a timestamping mechanism with a higher resolution.

Le Groupe de Recherche en Appareillage Médical de Sherbrooke (GRAMS) travaille actuellement sur un programme de recherche portant sur des photodiodes à avalanche monophotoniques (PAMP) opérées en mode Geiger en vue d'une application à la tomographie d’émission par positrons (TEP). Pour opérer dans ce mode, la PAMP, ou SPAD selon l’acronyme anglais (Single Photon Avalanche Diode), requiert un circuit d'étouffement (CE) pour, d’une part, arrêter l’avalanche pouvant causer sa destruction et, d’autre part, la réinitialiser en mode d’attente d’un nouveau photon. Le rôle de ce CE comprend également une électronique de communication vers les étages de traitement avancé de signaux. La performance temporelle optimale du CE est réalisée lorsqu’il est juxtaposé à la PAMP. Cependant, cela entraîne une réduction de la surface photosensible ; un élément crucial en imagerie. L’intégration 3D, à base d'interconnexions verticales, offr une solution élégante et performante à cette problématique par l’empilement de circuits intégrés possédant différentes fonctions (PAMP, CE et traitement avancé de signaux). Dans l’approche proposée, des circuits d’étouffement de 50 [mu]m x 50 [mu]m réalisés sur une technologie CMOS 130 nm 3D Tezzaron, contenant chacun 112 transistors, sont matricés afin de correspondre à une matrice de PAMP localisée sur une couche électronique supérieure. Chaque circuit d'étouffement possède une gigue temporelle de 7,47 ps RMS selon des simulations faites avec le logiciel Cadence. Le CE a la flexibilité d'ajuster les temps d'étouffement et de recharge pour la PAMP tout en présentant une faible consommation de puissance ( ~ 0,33 mW à 33 Mcps). La conception du PAMP nécessite de supporter des tensions supérieures aux 3,3 V de la technologie. Pour répondre à ce problème, des transistors à drain étendu (DEMOS) ont été réalisés. En raison de retards de production par les fabricants, les circuits n’ont pu être testés physiquement par des mesures. Les résultats de ce mémoire sont par conséquent basés sur des résultats de simulations avec le logiciel Cadence.

Time-Resolved diffuse optics is a powerful and safe technique to quantify the optical properties (OP) for highly scattering media such as biological tissues. The OP values are correlated with the compositions of the measured objects, especially for the tissue chromophores such as hemoglobin. The OP are mainly the absorption and the reduced scattering coefficients that can be quantified for highly scattering media using Time-Resolved Diffuse Optical Spectroscopy (TR-DOS) systems. The OP can be retrieved using Time-Resolved Diffuse Optical Imaging (TR-DOI) systems to reconstruct the distribution of the OP in measured media. Therefore, TR-DOS and TR-DOI can be used for functional monitoring of brain and muscles, and to diagnose some diseases such as detection and localization for breast cancer and blood clot. In general, TR-DOI systems are non-invasive, reliable, and have a high temporal resolution. TR-DOI systems have been known for their complexity, bulkiness, and costly equipment such as light sources (picosecond pulsed laser) and detectors (single photon counters). Also, TR-DOI systems acquire a large amount of data and suffer from the computational cost of the image reconstruction process. These limitations hinder the usage of TR-DOI for widespread potential applications such as clinical measurements. The goals of this research project are to investigate approaches to eliminate two main limitations of TR-DOI systems. First, building TR-DOS systems using custom-designed free-running (FR) and time-gated (TG) SPAD detectors that are fabricated in low-cost standard CMOS technology instead of the costly photon counting and timing detectors. The FR-TR-DOS prototype has demonstrated comparable performance (for homogeneous objects measurements) with the reported TR-DOS prototypes that use commercial and expensive detectors. The TG-TR-DOS prototype has acquired raw data with a low level of noise and high dynamic range that enable this prototype to measure multilayered objects such as human heads. Second, building and evaluating TR-DOI prototype that uses a computationally efficient algorithm to reconstruct high quality 3D tomographic images by analyzing a small part of the acquired data. This work indicates the possibility to exploit the recent advances in the technologies of silicon detectors, and computation to build low-cost, compact, portable TR-DOI systems. These systems can expand the applications of TR-DOI and TR-DOS into several fields such as oncology, and neurology. / Thesis / Doctor of Philosophy (PhD)