High-speed and Robust Integrated Silicon Nanophotonics for On-Chip Interconnects

Optical interconnects offer advantages over electrical interconnects such as higher bandwidth, low power, reduced interconnects delay, and immunity to electro-magnetic interference and signal crosstalk. However, in order for optical interconnects to be widely adopted, the technology must be made cost effective and must be simple to implement with CMOS electronics. Silicon photonics offers a great promise due to its inexpensive material and its compatibility with the current CMOS fabrication technology. Moreover, Silicon as a platform has the ability to integrate with different types of the optical components such as photodetector, modulator, light source, and waveguide to form a photonics integrated circuit. The goal of this work is to develop and fabricate devices that utilize a hybrid electronic-photonic integration to enable high performance optoelectronic computing and communication systems that overcome the barriers of electronics and dramatically enhance the performance of circuits and systems. We experimentally demonstrate a novel broadband optical time division multiplexer (OTDM) on a silicon chip. The system has a footprint× 700 micrometer and is inherently broadband with a bandwidth of over 100nm making it suitable for high-speed optical networks on chip. Also, we propose and fabricate a novel design to demultiplex the high bit rates of OTDM data using two differentially operated 5Gb/s modulators. Moreover, we propose a high-speed hybrid optical-time-division-multiplexing (OTDM) and wavelength-division-multiplexing (WDM) system that seamlessly generates high bit-rate data (\u3e200Gbit/s) from a low speed (5Gbit/s) quantum-dot mode locked laser pulse source. By utilizing time and wavelength domains, the proposed design is a promising solution for high-speed, compact and low-power consumption optical networks on chip. And finally, we experimentally demonstrate a robust, low insertion loss, compact Silicon ring resonator electro-optic modulator for Binary Phase Shift Key (BPSK) coding/decoding that encodes data in the phase of light. Our design improves significantly over recently demonstrated PSK modulator designs in terms of insertion loss and stability

Generic closed loop controller for power regulation in dual active bridge DC-DC converter with current stress minimization

This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) DC/DC converter using triple phase shift (TPS) control to enable closed loop power regulation while minimizing current stress. The key new achievements are: a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e. Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter AC RMS current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the RMS current in the entire bidirectional power range of - 1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool which is carefully analyzed to derive simple useful relations. Such relations enabled a generic closed loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate precision of the proposed closed loop controller under various operating conditions. An experimental prototype also substantiates the results achieved

Modular multilevel converter with modified half-bridge submodule and arm filter for dc transmission systems with DC fault blocking capability

Although a modular multilevel converter (MMC) is universally accepted as a suitable converter topology for the high voltage dc transmission systems, its dc fault ride performance requires substantial improvement in order to be used in critical infrastructures such as transnational multi-terminal dc (MTDC) networks. Therefore, this paper proposes a modified submodule circuit for modular multilevel converter that offers an improved dc fault ride through performance with reduced semiconductor losses and enhanced control flexibility compared to that achievable with full-bridge submodules. The use of the proposed submodules allows MMC to retain its modularity; with semiconductor loss similar to that of the mixed submodules MMC, but higher than that of the half-bridge submodules. Besides dc fault blocking, the proposed submodule offers the possibility of controlling ac current in-feed during pole-to-pole dc short circuit fault, and this makes such submodule increasingly attractive and useful for continued operation of MTDC networks during dc faults. The aforesaid attributes are validated using simulations performed in MATLAB/SIMULINK, and substantiated experimentally using the proposed submodule topology on a 4-level small-scale MMC prototype

A systems approach to determine how Toxoplasma gondii Infection causes neuropsychiatric disease

This thesis was previously held under moratorium from 16/03/2020 to 16/03/2022T. gondii infection acquired during life has been associated with psychoneurological disease in humans and behavioural changes in mice. However, less is known about the potential of congenitally acquired T. gondii infection, or for maternal T. gondii infection induced immune activation, to cause psychoneurological disease. The studies described herein, using LCMS (Liquid chromatography–mass spectrometry) demonstrate that adult acquired infection alters the neurochemistry and transcriptome of the brains of BALB/c mice. Notable changes to tryptophan, purine, arginine and carnitine metabolism were observed in infected mice. Congenitally infected and mice exposed to the maternal immune response to T. gondii, but not congenitally infected were found to have decreased mobility compared with control mice. Congenital T. gondii infection resulted in similar alterations in the neurochemistry of mice as seen in adult acquired infections. Some of these changes were observed, including tryptophan metabolism in mice exposed to the maternal immune response to T. gondii, but not congenitally infected. Both adult acquired T. gondii and congenital infection altered the brain transcriptome of mice relative to control uninfected mice with notable changes seen to transcripts of many immunologically important genes and enzymes in some of the metabolic pathways identified by LCMS. In addition, both adult acquired T. gondii infection, congenital infection and maternal exposure to different degrees were found to induce changes in a number of additional transcripts previously associated with psychoneurological diseases. These results demonstrate that maternal exposure to T. gondii infection during pregnancy induces a subset of neurochemical and transcriptomic changes found in mice with adult acquired and congenital T. gondii infection. The results therefore reinforce the potential of maternal immune activation to affect psychoneurological diseases and implicate T. gondii as a potential aetiological agent of this process.T. gondii infection acquired during life has been associated with psychoneurological disease in humans and behavioural changes in mice. However, less is known about the potential of congenitally acquired T. gondii infection, or for maternal T. gondii infection induced immune activation, to cause psychoneurological disease. The studies described herein, using LCMS (Liquid chromatography–mass spectrometry) demonstrate that adult acquired infection alters the neurochemistry and transcriptome of the brains of BALB/c mice. Notable changes to tryptophan, purine, arginine and carnitine metabolism were observed in infected mice. Congenitally infected and mice exposed to the maternal immune response to T. gondii, but not congenitally infected were found to have decreased mobility compared with control mice. Congenital T. gondii infection resulted in similar alterations in the neurochemistry of mice as seen in adult acquired infections. Some of these changes were observed, including tryptophan metabolism in mice exposed to the maternal immune response to T. gondii, but not congenitally infected. Both adult acquired T. gondii and congenital infection altered the brain transcriptome of mice relative to control uninfected mice with notable changes seen to transcripts of many immunologically important genes and enzymes in some of the metabolic pathways identified by LCMS. In addition, both adult acquired T. gondii infection, congenital infection and maternal exposure to different degrees were found to induce changes in a number of additional transcripts previously associated with psychoneurological diseases. These results demonstrate that maternal exposure to T. gondii infection during pregnancy induces a subset of neurochemical and transcriptomic changes found in mice with adult acquired and congenital T. gondii infection. The results therefore reinforce the potential of maternal immune activation to affect psychoneurological diseases and implicate T. gondii as a potential aetiological agent of this process

Electro-absorption of silicene and bilayer graphene quantum dots

We study numerically the optical properties of low-buckled silicene and AB-stacked bilayer graphene quantum dots subjected to an external electric field, which is normal to their surface. Within the tight-binding model, the optical absorption is calculated for quantum dots, of triangular and hexagonal shapes, with zigzag and armchair edge terminations. We show that in triangular silicene clusters with zigzag edges a rich and widely tunable infrared absorption peak structure originates from transitions involving zero energy states. The edge of absorption in silicene quantum dots undergoes red shift in the external electric field for triangular clusters, whereas blue shift takes place for hexagonal ones. In small clusters of bilayer graphene with zigzag edges the edge of absorption undergoes blue/red shift for triangular/hexagonal geometry. In armchair clusters of silicene blue shift of the absorption edge takes place for both cluster shapes, while red shift is inherent for both shapes of the bilayer graphene quantum dots.Comment: 7 pages, 7 figure

Modified dual active bridge DC/DC converter with improved efficiency and interoperability in hybrid LCC/VSC HVDC transmission grids

DC transmission grids are the promising electrical networks in the near future especially with the high penetration of large scale renewables. This paper proposes a modified version of the dual active bridge (DAB) DC/DC converter with AC link capacitors generating reactive power to compensate for non-active power consumption; hence mitigating current stresses and losses to improve efficiency. The proposed topology also enables the connectivity of current source line-commutated HVDC and voltage source HVDC technologies particularly during power reversal; a feature which conventional DAB is incapable of doing. Analysis and detailed design of the proposed converter are addressed and a comparative performance analysis is carried out with conventional DAB. Converter principle of operation is explained and Matlab/Simulink simulations are carried out to verify converter operation particularly under adverse conditions such as rated power reversal and DC fault conditions. A low scale prototype substantiates the theoretical analysis and simulation results

Enhanced performance modified discontinuous PWM technique for three phase Z-source inverter

Various industrial applications require a voltage conversion stage from DC to AC. Among them, commercial renewable energy systems (RES) need a voltage buck and/or boost stage for islanded/grid connected operation. Despite the excellent performance offered by conventional two-stage converter systems (DC-DC followed by dc-ac stages), the need for a single-stage conversion stage is attracting more interest for cost and size reduction reasons. Although voltage source inverters (VSIs) are voltage buck-only converters, single stage current source inverters (CSIs) can offer voltage boost features, although at the penalty of using a large DC-link inductor. Boost inverters are a good candidate with the demerit of complicated control strategies. The impedance source (Z-source) inverter is a high-performance competitor as it offers voltage buck/boost in addition to a reduced passive component size. Several pulse width modulation (PWM) techniques have been presented in the literature for three-phase Z-source inverters. Various common drawbacks are annotated, especially the non-linear behavior at low modulation indices and the famous trade-off between the operating range and the converter switches' voltage stress. In this paper, a modified discontinuous PWM technique is proposed for a three-phase z-source inverter offering: (i) smooth voltage gain variation, (ii) a wide operating range, (iii) reduced voltage stress, and (iv) improved total harmonic distortion (THD). Simulation, in addition to experimental results at various operating conditions, validated the proposed PWM technique's superior performance compared to the conventional PWM techniques