1,243 research outputs found
Analytical validation of innovative magneto-inertial outcomes: a controlled environment study.
peer reviewe
Toward an active CMOS electronics-photonics platform based on subwavelength structured devices
The scaling trend of microelectronics over the past 50 years, quantified by Moore’s Law, has faced insurmountable bottlenecks, necessitating the use of optical communication with its high bandwidth and energy efficiency to further improve computing performance.
Silicon photonics, compatible with CMOS platform manufacturing, presents a promising means to achieve on-chip optical links, employing highly sensitive microring resonator devices that demand electronic feedback and control due to fabrication variations. Achieving the full potential of both technologies requires tight integration to realize the ultimate benefits of both realms of technology, leading to the convergence of microelectronics and photonics.
A promising approach for achieving this convergence is the monolithic integration of electronics and photonics on CMOS platforms. A critical milestone was reached in 2015 with the demonstration of the first microprocessor featuring photonic I/O (Chen et al, Nature 2015), accomplished by integrating transistors and photonic devices on a single chip using a monolithic CMOS silicon-on-insulator (SOI) platform (GlobalFoundries 45RFSOI, 45 nm SOI process) without process modifications, thus known as the "zero-change" approach. This dissertation focuses on leveraging the fabrication capabilities of advanced monolithic electronic-photonic 45 nm CMOS platforms, specifically high-resolution lithography and small feature size doping implants, to realize photonic devices with subwavelength features that could potentially provide the next leap in integrated optical links performance, beyond microring resonator based links.
Photonic crystal (PhC) nanobeam cavities can support high-quality resonance modes while confining light in a small volume, enhancing light-matter interactions and potentially enabling ultimate efficiencies in active devices such as modulators and photodetectors. However, PhC cavities have been overshadowed by microring resonators due to two challenges. First, their fabrication demands high lithography resolution, which excludes most standard SOI photonic platforms as viable options for creating these devices. Secondly, the standing-wave nature of PhC nanobeam cavities complicates their integration into wavelength-division multiplexing (WDM) optical links, causing unwanted reflections when coupled evanescently to a bus waveguide.
In this work, we present PhC nanobeam cavities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. The devices were fabricated in a 45 nm monolithic electronics–photonics CMOS platform optimized for silicon photonics, GlobalFoundries 45CLO, exhibiting a quality factor in excess of 100,000 the highest among fully cladded PhC nanobeam cavities in any SOI platform. Furthermore to eliminate reflections, we demonstrate an approach using pairs of PhC nanobeam cavities with opposite spatial mode symmetries to mimic traveling-wave-like ring behavior, enabling efficient and seamless WDM link integration. This concept was extended to realize a reflectionless microring resonator unit with two microrings operating as standing-wave cavities. Using this scheme with standing-wave microring resonators could lead to an optimum geometry for microring modulators with interdigitated p-n junctions in terms of modulation efficiency in a manner that allows for straightforward WDM cascading.
This work also presents the first demonstration of resonant-structure-based modulators in the GlobalFoundries 45CLO platform. We report the first-ever demonstration of a PhC modulator in a CMOS platform, featuring a novel design with sub-wavelength contacts on one side allowing it to benefit from the "reflection-less"' architecture. Additionally, we also report the first demonstration of microring modulators. The most efficient devices exhibited electro-optical bandwidths up to 30 GHz, and 25 Gbps non-return-to-zero (NRZ) on-off-keyed (OOK) modulation with 1 dB insertion loss and 3.1 dB extinction ratio.
Finally, as the complexity of silicon photonic systems-on-a-chip (SoC) increases to enable new applications such as low-energy data links, quantum optics, and neuromorphic computing, the need for in-situ characterization of individual components becomes increasingly important. By combining Near-field scanning optical microscopy (NSOM) with a flip-chip post-processing technique, this dissertation demonstrates a method to non-invasively perform NSOM scans of a photonic device within a large-scale CMOS-photonic circuit, without interfering with the performance and packaging of the photonics and electronics, making it a valuable tool for future development of high performance photonic circuits and systems
The 2023 wearable photoplethysmography roadmap
Photoplethysmography is a key sensing technology which is used in wearable devices such as smartwatches and fitness trackers. Currently, photoplethysmography sensors are used to monitor physiological parameters including heart rate and heart rhythm, and to track activities like sleep and exercise. Yet, wearable photoplethysmography has potential to provide much more information on health and wellbeing, which could inform clinical decision making. This Roadmap outlines directions for research and development to realise the full potential of wearable photoplethysmography. Experts discuss key topics within the areas of sensor design, signal processing, clinical applications, and research directions. Their perspectives provide valuable guidance to researchers developing wearable photoplethysmography technology
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Implementation of a real time Hough transform using FPGA technology
This thesis is concerned with the modelling, design and implementation of efficient architectures for performing the Hough Transform (HT) on mega-pixel resolution real-time images using Field Programmable Gate Array (FPGA) technology. Although the HT has been around for many years and a number of algorithms have been developed it still remains a significant bottleneck in many image processing applications.
Even though, the basic idea of the HT is to locate curves in an image that can be parameterized: e.g. straight lines, polynomials or circles, in a suitable parameter space, the research presented in this thesis will focus only on location of straight lines on binary images. The HT algorithm uses an accumulator array (accumulator bins) to detect the existence of a straight line on an image. As the image needs to be binarized, a novel generic synchronization circuit for windowing operations was designed to perform edge detection. An edge detection method of special interest, the canny method, is used and the design and implementation of it in hardware is achieved in this thesis.
As each image pixel can be implemented independently, parallel processing can be performed. However, the main disadvantage of the HT is the large storage and computational requirements. This thesis presents new and state-of-the-art hardware implementations for the minimization of the computational cost, using the Hybrid-Logarithmic Number System (Hybrid-LNS) for calculating the HT for fixed bit-width architectures. It is shown that using the Hybrid-LNS the computational cost is minimized, while the precision of the HT algorithm is maintained.
Advances in FPGA technology now make it possible to implement functions as the HT in reconfigurable fabrics. Methods for storing large arrays on FPGA’s are presented, where data from a 1024 x 1024 pixel camera at a rate of up to 25 frames per second are processed
LIPIcs, Volume 261, ICALP 2023, Complete Volume
LIPIcs, Volume 261, ICALP 2023, Complete Volum
Orientation control during 2D-3D composite preforming
Non-crimp fabrics (NCFs) are employed in composite structures as an alternative to woven fabrics when there is a requirement for improved tensile strength and modulus. To exploit NCF properties, components are designed with optimised fibre directions that reinforce the predicted load paths. 2D to 3D composite forming is a manufacturing method that has been developed for automation, to improve the labour economy of components and reduce per unit costs. Currently it is difficult to maintain accurate fibre orientation control due to the constraints of the 2D pre-form and the lack of interaction with the fabric during its transition from a 2D to a 3D form.
This thesis explores process alterations that improve fibre orientation control in 2D-3D forming through the introduction of multiple forming stages. Thus enabling the implementation of optimised NCF layups in formed components. The approach has been broken down into the following research areas:
Analysis of fibre angle distribution: A robust method for the full field measurement of fibre angle distribution has been created and validated to ±0.5 degrees for in-plane testing and ±3 degrees on double curvature surfaces. It has been shown that the theoretical calculation of shear angle from the bias extension test for an NCF is incorrect above shear angle values of 15 degrees. Whereas, theoretical shear angle calculations for NCFs in the picture frame test are accurate to within ±1 degree. It was found that shearing causes a non-linear variation in the tensile properties of an NCF due to fibre misalignment that has previously been unmeasured. NCFs can experience an undesirable reduction in tensile properties at shear angles that are commonly found in 2D-3D formed components.
Analysis of fibre misalignment due to inter-stitch buckling defects: It was found that a deformation mode occurs in NCFs at very low shear angles (0 degrees to 1 degree) where frictional interactions between the yarns prevents slippage at the stitch points. This causes a non-linear shear region at low shear angles observed for many NCF shear force/angle graphs. An analytical model was created to show the link between the initial non-linear shear region and the inter-stitch buckling defects that has been proved to impact fibre misalignment at higher shear angles. To improve fibre alignment, two buckling defect reduction strategies were developed as a result of the modelling and applied to 2D and 3D samples. During in-plane testing localised stitch removal showed a 51% reduction in fibre misalignment and resin lubrication presented a 57% reduction. These strategies combat the undesirable reduction in properties due to fibre misalignment, enabling multiple forming cycles to be conducted without negatively impacting the fabric structure.
Modelling multiple forming cycles: A novel multi-cycle finite element material model was created, that accurately captures the previously undocumented hysteresis phenomenon found in NCFs when subjected to multiple shear cycles. This was validated to within 8% of experimental values during in-plane testing. A multi-stage double diaphragm forming process has been developed that locally induces regions of high shear with the objective of taking advantage of the multi-cycle hysteresis in the fabric. The process alteration generated a 25% reduction in the maximum defect size found on a double curvature component, highlighting the formability benefits of a multiple stage processes and validating the model.
Fibre continuity control during forming: A process alteration has been developed to show that plies running longitudinally along a formed component can be successfully pre-sheared before the forming operation to locally align fibres in the desired orientation. A structural simulation was created that combined the multi-cyclic material model and the non-linear structural behaviour of sheared fabrics. The results for a simple beam showed that a pre-sheared laminate has a higher peak stress under all the tested load cases and an improvement to mechanical stiffness which was shown to be transferable to a component weight reduction of 17% through ply removal. The pre-shearing process also generated a reduction in the wastage from trimming fabrics. The overall fabric area needed for simple beam like geometries was reduced by 15.5%-34.5%. A complex beamlike demonstrator was modelled and showed a 31% improvement to material utilisation and 11% improvement to mechanical stiffness.
The thesis chapters progress the idea of fibre alignment control in 2D-3D forming from: measurement), to understanding, into modelling, and finally a demonstration of the application. Ideas from each chapter can be applied to current industrial processes and improve the capabilities of components made using 2D-3D forming
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