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Grid of nine different traffic users.mp4
No full textThis video is from data collected for my PhD research in the Ho Chi Minh City traffic system during the years 2015-2017. It shows a grid of the perspective of 9 different kinds of traffic users in the urban traffic simultaneously. These video perspectives were shot using GoPro and they include vehicles such as motorcycle delivery riders, truck drivers, bus drivers, a lottery ticket seller, and Vietnamese and non-Vietnamese traffic users.</p
Polyvalent interaction and confinement to suppress polysulfide dissolution and improve electrocatalysis
No full textSulfur undergoes various changes from solid S8 to soluble lithium polysulfides(Li2S8-Li2S4) and insoluble Li2S2 and Li2S during charge-discharge cycling of lithium sulfur (Li-S) batteries. The dissolution of sulfur-containing compounds in battery electrolytes and their movement between electrodes, known as the polysulfide shuttle effect, decreases the battery performance. In addition, the kinetics of sulfur redox reactions are sluggish. Different host materials have been explored to address these issues. Herein, nanofibres of conjugated polymer have been synthesised that have multiple electron transport pathways. The cross-linker is a nickel phthalocyanine tetrasulfonic acid tetrasodium salt (NPTS). The sulfur is situated in the voids of the cross-linked nanofibres of the polymer and the Ni2+ present in the NPTS attracts the negative charge-bearing polysulfides. Due to the confinement and polyvalent electrostatic attraction, the solubility of the sulfur and polysulfide is suppressed. Density Functional Theory calculations revealed that the S2- interacts with Ni2+ and Li+ interacts with the pyrrolic nitrogens of PPy-NPTS. The overlap of the p orbitals of sulfur and nickel is determined from the Density of States calculations. The bond length of Li2S is ideal for this interaction, hence this molecule showed the highest adsorption energy with the cross-linked polymeric host. The adsorption energy decreased upon an increase in the number of sulfur atoms in the polysulfide due to the bond length mismatch. However, due to electrostatic polyvalent interaction, the adsorption energy is sufficient to suppress polysulfide dissolution. Thus, the structure of this host material with nickel cations and pyrrolic nitrogens is suitable to adsorb lithium polysulfides irrespective of their length, unlike neutral hosts. This efficient binding also improved the electrocatalysis of the sulfur redox reaction. Hence, the Li-S battery containing these nanofibres showed a specific capacity of 1326 mA h/g at 0.2 C. Batteries fabricated considering practical parameters, such as low electrolyte to sulfur ratio of 5.0 μL/mg with sulfur loading of 4.0 mg/cm2, showed impressive performance.</p
Behavioral Intention to Adopt Precision Agriculture – A Study of Vietnamese Smallholder Rice Farmers
No full textGlobal agriculture is under the pressure of efficiency and sustainability. The overuse of fertilizers, chemicals, and water has led to issues associated with environmental safety and waste. Vietnam shares similar agricultural challenges with other countries. The inefficiency in input usage and low profitability in farming pose an urgent need to innovate current practices. Precision agriculture (PA) emerges as a potential solution, offering a system approach to make agricultural activities more efficient and sustainable with optimal input. While PA technology is prevalent in developed economies, its concept remains novel to Vietnamese smallholder rice farmers. This prompted an investigation into the factors influencing these farmers' intentions (BI) to adopt PA technology. Therefore, four research objectives have been listed to be addressed in this research: (1) to explore different views of various stakeholders on the potential for and necessity of PA adoption among smallholder rice farmers; (2) to identify potential factors that affect the behavioral intention of smallholder rice farmers in Vietnam towards adopting PA technology; (3) to investigate how the performance of cooperatives and other key factors influence the intention of smallholder rice farmers in Vietnam to adopt PA technology; (4) to systematically identify and analyze the various combinations of causal conditions that influence the behavioral intention of smallholder rice farmers in Vietnam to adopt PA technology. In order to accomplish the objectives, this research was conducted in two distinct phases. The initial phase involved semi-structured interviews aimed at collecting feedback from farmers and experts to primarily validate and extend the proposed research model. The subsequent phase focused on quantitative data collection from a sample of 600 smallholder farm owners to test 18 hypotheses examining various factors that directly and indirectly affect BI to adopt PA. The quantitative data was analyzed using structural equation modeling (SEM) complemented by Necessary Condition Analysis (NCA) and fuzzy-set Qualitative Comparative Analysis (fsQCA) to examine the effects of individual factors and combinations of factors on the intention of farmers to adopt PA technology. This qualitative phase discussed performance expectancy (PE), effort expectancy (EE), government support (GS), social influences (SI), internal facilitating conditions (FC), and the performance of agricultural cooperatives (COOP) as outstanding themes guided by the extended UTAUT model. The technology’s observability (OBSV) and trialability (TRIA) were found to potentially affect farmers’ performance expectancy and effort expectancy. Additionally, as grounded from the interviews, the support from lead firms is a newly emerging themes that play a crucial role in facilitating the adoption of PA technology among Vietnamese smallholder rice farmers. This new theme was added to the proposed research model to be tested in the quantitative phase. The quantitative analysis through SEM showed that factors like PE, EE, SI, GS, and LEAD significantly influenced farmers' intention to embrace PA technology. On the contrary, internal FC did not show a significant effect on BI. Importantly, the role of agricultural cooperatives as innovation intermediaries was found to significantly moderate the impact of GS and LEAD on BI. Additionally, multi-group analysis (MGA) highlighted that a farmer's age plays a crucial role in moderating the effect of SI on BI, with older farmers showing a stronger positive response. Moreover, the application of fsQCA aimed to enrich the SEM findings, identifying five distinct condition combinations that reliably lead to BI. These combinations include PE, EE, SI, GS, and LEAD; PE, EE, SI, LEAD, and COOP; PE, SI, GS, LEAD, and COOP; PE, EE, SI, GS, COOP, with a negation of FC; and PE, EE, GS, LEAD, COOP, with the absence of FC. This diversity in pathways illustrates equifinality, indicating that various combinations of factors can result in the same end goal: a strong intention to adopt PA technology. The persistence of this intention to adopt, despite less favorable internal circumstances, highlights the importance of external support mechanisms (from lead firms, the government, and cooperatives). NCA aligns with the fsQCA results, emphasizing that PE is an indispensable factor for a strong farmers’ intention to adopt. This necessity of PE is echoed across all identified configurations, highlighting its critical role in achieving the desired outcome. This alignment between NCA and fsQCA underscores the validity and strength of the configurational approaches used.The findings from this research not only enhance the understanding of PA and its potential adoption in Vietnam but also provide insights that can guide policy adjustments and the creation of initiatives to promote PA adoption among Vietnamese farmers. A notable aspect of this research is its innovative approach to extending the renowned Unified Theory of Acceptance and Use of Technology (UTAUT) model. It underscores the importance of external support from lead firms and the government, while also emphasizing the moderating role of a cooperative's performance. This contribution offers a fresh perspective on the factors influencing technology adoption in agriculture. Furthermore, the application of NCA and fsQCA in this research provides a more nuanced conceptualization of PA adoption, which has been ignored by prior research in the field. By the time of the thesis submission, the researcher successfully published two journal articles based on the thesis content. The first article, a systematic literature review, was drawn from Chapter 2, while the second, focusing on qualitative findings, emerged from Chapter 4. Additionally, a third article is currently under review; this paper employs a combination of SEM and fsQCA methodologies, as detailed in Chapter 5 of the thesis.</p
Work readiness of project management graduates in construction: a multi-method multi-vocal qualitative study
No full textWork readiness encompasses an individual's competence in a range of attributes that enable him/her to successfully transition into work. While continuing to gain increasing interest worldwide, the concept of work readiness remains one that is difficult to define. Literature on the work readiness of graduates in the project management profession is scarce. This PhD study addresses this lack by exploring work readiness within the context of the project management discipline and the Australian construction industry. Given the complexity of the concept of work readiness, the research framework drew on the multiple theoretical lenses of Stakeholder Theory, Human Capital Theory and Matching Theory as well as the underlying principles of the Resource-Based View and the Shared Value Perspective. This research adopted a multi-method research strategy consisting of three interdependent phases. The first phase used a document analysis of program learning outcomes of all fourteen project management bachelor's degrees offered in Australia to explore the work-ready attributes embedded in Australian project management degree programs. The second phase adopted a multi-vocal holistic embedded case study design. Seventy-five semi-structured in-depth interviews were conducted with five stakeholder groups with a vested interested in project management education and the pathway into construction (current students, educators, recent graduates, employers and project professional bodies). This phase explored the different stakeholders' perspectives of work readiness within the project management discipline. The inclusion of both the students' and graduates' voices is novel since these voices have been largely silent in the work-readiness discourse to date. The third and final phase of the research entailed a focus group with key informants from the five key stakeholder groups to validate the findings and generate evidence-based recommendations for the enhancement of the work readiness of emerging project management professionals within the construction industry.
As well as identifying the work-readiness attributes embedded in current Australian undergraduate project management degrees, this research has also consolidated the fragmented perspectives of five major stakeholders to develop an integrated holistic understanding of what constitutes work readiness for project management graduates working in construction. The results of this research show that i) work-readiness attributes are contextual and may vary based on country, university, and school where the degree is offered, ii) misalignments exist between stakeholder perspectives with an observed divide between stakeholders with industry experience and those without, and iii) while all stakeholders value work readiness, there is limited stakeholder collaboration towards its development. Finally, this research puts forward a set of evidence-based practical recommendations which can be exercised by the five stakeholder groups to encourage a collective, collaborative strategy to enhance student work readiness. The results of this research may be of value to universities offering undergraduate project management degrees, which have an interest in considering the perspectives of industry employers, peak professional bodies, as well as their graduates and students when looking to build upon their work-readiness initiatives. In addition, it is expected that the recommendations from this research will have benefits for employers and project management professional bodies as well as for undergraduate project management students and graduates who wish to pursue careers in the Australian construction industry.</p
Studies on porous organic polymers and their nanocomposites for electrocatalytic and biological applications
No full textPorous organic polymers (POPs) are a promising class of porous materials which contain organic building blocks that are interwoven via strong covalent bonds. In the recent decade, there has been rising attention in POPs as nanoreactors for heterogeneous catalysis (electrochemical, biological, thermal, and photochemical) due to their structural diversity which implies large surface areas, high chemical, and thermal stabilities, tuneable pore size distributions, and adjustable chemical functionalities. These salient structural features have allowed work on different synthetic strategies for constructing various POP materials to influence their functionality and study their impressive application as future generation nanoreactors. The above-mentioned characteristics of POP-based materials makes them useful as electrocatalysts, as they offer the potential for preparation of either metal-free or metallated polymer catalysts that favour electrocatalytic reduction of CO2 into value-added products, and production of clean H2 and O2 from water. In addition, antibacterial applications have been studies for POPs, as physical damage of bacterial cell walls can be caused by their structure.
This thesis emphasizes the integration of different synthetic methods, and the application of POPs as a catalyst that offers opportunities in next generation for the synthesis of functional materials with vital effect in both applied and basic research areas. In this present work, the POP reactivity is tailored for specific applications by fine starting materials in the synthetic procedures.
Initially, we focused on the synthesis and electrochemical applications of phloroglucinol, 1,4-phenylenediamine and triazine (PPT-POP) based covalent triazine frameworks (CTF). The skeletal structure of synthesized CTF has a large amount of ‘N’ content that results in excellent stability (chemical and thermal) and catalytic activity. Due to their large surface areas, they are often used as electrocatalysts as well as in energy storage applications. Furthermore, the carbonization of CTF at high temperatures under an inert atmosphere lead to the decomposition of the framework structure. It is noted that an increase in carbonization temperature improves the degree of graphitization, thereby yielding N-doped carbon materials with high porosity and active sites which are essential for improved catalytic activity. In this aspect, we reported the synthesis and application of a new carbonized porous organic polymer materials based on triazine and its electrocatalytic performance towards electrocarboxylation, hydrogen-evolution, and oxygen-evolution reactions.
As a next step, an o-tolidine based triazine polymer (TTP) was synthesized by adopting the above synthetic route with o-tolidine as a starting material instead of 1,4-phenylenediamine for validating and comparing the catalytic activity with PPT-POP. The synthesized TTP had a large surface area for electro-catalysis applications, which combined with high ‘N' content, and excellent chemical and thermal stability, allowing exploration of catalytic and energy storage applications. Also, the structural flexibility and tunability allow precise modulation for the desired applications. The triazine interconnects allowed the introduction of a metal ion/metal oxide via coordination, which is known to further enhance the conductivity and catalytic properties. It was thus demonstrated that the synthesis of o-tolidine based triazine (TTP) covalent organic frameworks and modification of the surface with Cu, Ni and Cu-Ni alloy, allowed electrocatalysis of the electrocarboxylation of epoxide to cyclic carbonate, and water splitting reactions.
In the next step, we introduced metal ions into the 1,4-phenylenediamine based covalent organic polymer (PD-COP) to investigate the electrochemical behaviour. Metal ion decoration on PD-COP polymers allows the synthesis a range of new types of micro-and mesoporous (2–50 nm) materials, involving amorphous organic polymers and crystalline COPs as active and selective electrocatalysts. Au nanoparticles (NPs) decorated on COP have been frequently used by electrochemists due to their catalytic activity. For electrocatalysis towards total water splitting (TWS) in an alkaline medium, to date, there is no report on Au NPs decorated on COP. Herein, we attempted to use Au NPs modified COP as an electrocatalyst for water splitting in an alkaline medium. We proposed a facetious route for the incorporation of Au NPs on COP involving sodium borohydride (NaBH4) reduction. It is noteworthy to mention that the excess amine sites on the COP act as a stabilizing agent. In this step, we reported the development of an Au NPs decorated polymer catalyst with for total water splitting, wherein the as-prepared catalysts show excellent catalytic activity.
Finally, we focused on a biological application of the initially synthesized COP which are scarcely studied and reported in the literature. The COF has a high specific surface area and porosity and hence finds applications in gas storage/CO2 reduction, battery materials, chemical sensors, gas/chemical separation, catalysis processes, and light-emitting materials. To date, many of these reported applications are based on their physical and chemical properties, and very little has been explored on their biological properties/applications. While the physical and chemical properties highly depend on the specific surface area, nature of interactions in the pores, and pore size, the biological applications completely rely on aspects such as biocompatibility and anti-fungal/antiviral behavior. In the present work, we reported the synthesis of o-tolidine and triazine interlinked covalent organic polymer (oTT-COP) and its antibacterial activity towards Staphylococcus aureus and Pseudomonas aeruginosa (gram-positive and gram-negative) respectively. The antibacterial activity of PPT-COP (phenylene diamine, phloroglucinol interlinked triazine covalent organic polymer) was evaluated to understand the role of the amine group on the polymer network towards antibacterial activity.
Overall, we have successfully synthesized and characterized various porous organic polymers (phenylene diamine, phloroglucinol and o-tolidine-based POPs) and their nanocomposites containing various metal ions such as Cu, Ni, Cu-Ni and Au. The catalytic properties were studied for electrocarboxylation, and water splitting (HER and OER). Furthermore, the synthesised phenylene diamine, phloroglucinol and o-tolidine-based metal free POPs were used in biological studies for the first time
Improving satellite connectivity using artificial intelligence and inter-satellite links
No full textThe rapid expansion of the Internet of Things (IoT) through the last decade has allowed billions of devices and sensors to exchange vast amounts of data wirelessly, revolutionizing connectivity across smart appliances, automobiles, and urban infrastructure. This technological leap has necessitated advancements at the base stations where managing such extensive data exchange is intricate. Artificial intelligence emerges as a pivotal solution, with its proven prowess in handling complex, high-dimensional datasets in signal processing, computer vision, speech recognition, and more, by learning from data directly without the need for explicit programming.
As IoT technology extends its reach beyond terrestrial bounds into satellite communications, the importance of global connectivity comes into sharp focus. Satellites play a crucial role where terrestrial networks cannot suffice, but they introduce unique challenges, primarily energy constraints. Therefore, while traditional deep learning is instrumental in terrestrial IoT, it must be adapted to suit the energy-efficient requirements of satellite networks. This adaptation leads to the exploration of Spiking Neural Networks (SNNs), which offer a promising avenue for handling the energy efficiency needed in satellite IoT communications.
This dissertation delves into the role of artificial intelligence in addressing the complexities of next-generation wireless communications for IoT. It presents novel artificial intelligence frameworks tailored for signal detection in both terrestrial and satellite IoT networks, advocating for learning-based spectrum sensing and the development of energy-efficient inter-satellite-link (ISL) topologies within large satellite constellations. The study aims to demonstrate that by harnessing the power of artificial intelligence, it can effectively surmount the challenges presented by the IoT's vast scale and the energy limitations of satellite networks.
One of the key advantages of artificial intelligence techniques is their ability to automatically extract relevant features from the input data. For example, in the case of oscillator offset conditions, artificial intelligence techniques can be trained on large datasets of signals with varying degrees of frequency and time offset, enabling them to learn the underlying patterns and characteristics of signals affected by this offset. The techniques can then use this knowledge to accurately detect and classify signals even when a significant oscillator offset is present. As such, using deep learning networks for IoT signal detection on signals impaired with oscillator offset is one of the investigated topics in this thesis.
Another prominent issue in next-generation IoT networks is that high device density, which inherently leads to elevated levels of co-channel interference. This generally occurs when two or more signals are occupying the same frequency band at the same time and accordingly interfering with each other resulting in a degradation in the quality of the communication link. This can result in an incorrect signal demodulation/detection by the base station which then requires re-transmission by the user device. This is particularly a challenge for low-power devices as re-transmission results in higher energy consumption, a luxury that is not always available for IoT devices. To enhance the robustness of signal detection, this dissertation also explores deep learning networks for signal detection under co-channel interference scenarios.
Furthermore, for resource-constrained base stations (receivers) such as low-Earth orbit (LEO) satellite terminals, SNNs have emerged to provide a promising solution for achieving energy-efficient inference. Unlike digital-based artificial neural networks, SNNs are designed to mimic the behavior of biological neurons, allowing them to operate more efficiently and with lower power consumption. The thesis investigates utilizing SNNs for signal detection with an elevated level of co-channel interference as well as for wideband Frequency spectrum analysis.
In addition, one area that can be used to increase energy efficiency in satellites is the design of an ISL topology for direct communication between satellites within a mega-satellite constellation. In this thesis, energy-efficient ISL topologies are explored, where a novel topology is proposed that constructs optimized ISLs. Once the topology is constructed, a classical algorithm is employed to find the shortest possible path between any two satellites within a constellation.
In this thesis, mathematical analysis is utilized to investigate the merits of the proposed methods in addition to Monte Carlo analysis using computer simulations to test the hypotheses. Furthermore, the experimental results are compared with baseline schemes, from state-of-the-art literature, to showcase the benefits of the proposed solutions. The majority of the findings presented in this dissertation have been published, in part or, in well-respected peer-reviewed journals and conference proceedings, or are currently undergoing the peer-review process. These publications are duly highlighted and identified throughout this thesis
Heat transfer enhancement using ferrofluid under magnetic fields
No full textThe miniaturisation of electronic devices has resulted in the need for improved micro- and nanoscale heat transfer solutions. Various cooling techniques have been analysed in recent years, and the data suggests that forced convective and spray liquid cooling will play a crucial role in thermal management practices. Due to their unique properties, ferrofluids, known as magnetite nanofluids, have garnered interest as potential heat transfer solutions. These suspensions of magnetic nanoparticles in a liquid carrier can respond to external magnetic fields, altering their thermal properties and behaviour. This makes ferrofluids an attractive option for heat transfer, as they can be controlled and manipulated in ways impossible with conventional liquids. Based on this information, this thesis is divided into two main areas: convective heat transfer and droplet impingement using a ferrofluid. The goal is to understand the convective heat transfer characteristics of ferrofluids in a microchannel under a magnetic field and analyse the heat transfer of the ferrofluid droplets. Simulations and experimental studies have been used to determine the heat transfer performance of ferrofluids in a microchannel under different external magnetic fields. The impact of magnetic fields on the heat transfer characteristics of the ferrofluid droplets will be studied under microscale conditions. The droplets’ size and their impingement velocity will be controlled to ensure consistent conditions. The temperature of the solid surface has been measured to determine the heat transfer performance of the ferrofluid droplets.
The results of this research provide insight into the impact of magnetic fields on the heat transfer characteristics of ferrofluids under microscale conditions. This information will be helpful for engineers and researchers in the field of thermal management, as it will provide a foundation for the design of more effective and efficient cooling systems for electronic devices
The governance of urban greenspace in Dhaka City, Bangladesh
No full textThe governance of urban greenspace is critical for sustainable development since it is the space where policies and programmes, the roles and responsibilities of different actors, approaches, resource implications, and partnerships unfold. While there exists a substantial amount of study on urban greenspace, there is a noticeable dearth of studies focusing on the governance aspect of urban greenspace in the Global South. Given the importance of urban greenspace and the presence of governance challenges in the Global South, research on the governance of urban public greenspace is critical. With a specific emphasis on Dhaka city, Bangladesh, a rapidly expanding Asian metropolis, this PhD research aims to explore how and in what ways the governance of urban public greenspace supports and promotes sustainable development. Given the various types of urban greenspace, the study focuses on public parks and playgrounds.
Using a qualitative case study research approach, the study investigates the institutional arrangements, including the role of different actors, the decision-making process, politics, and informalities in the development process of public greenspace, and critically engages with - whose interests are sustained in the development process, and outlines the challenges and opportunities to support sustainable development. The data collection process involves 21 key informant interviews and examines five cases of public parks and playgrounds. Additionally, relevant secondary sources, such as newspaper articles, reports, and official documents, are utilized to validate and support the interview data. The collected data is analyzed thematically using a combination of inductive and deductive approaches to identify emerging themes.
Key findings from the research are that multiple government or public authorities are responsible for provisioning and managing public greenspace in Dhaka city. The involvement of NGOs is limited to policy advocacy, campaigns, and protests. A limited number of community-based organisations are primarily engaged in the management of public parks, and their involvement is contingent upon specific contextual factors such as the socioeconomic status of the community, and the location of the park. Public participation is principally confined to the city corporation’s election, while public consultation is tokenistic.The public greenspace development decisions are fragmented due to the involvement of multiple actors and the lack of coordination among the actors. The decision-making process for greenspace development exhibits a reactive approach. The dominant power of the mayor, the financial capacity of the institution, the national interests, or the influence of the central government all affect the development decision. Furthermore, the clientelist political culture, bureaucratic authority and local elites influence the decision. As a result, public greenspace development decisions lead to the emergence of elite capture, privatisation, expulsion, social segregation, and the rise of grey structures over greenspace, all of which pose significant challenges to sustainable development.
This research contributes to addressing the significant knowledge and policy gaps around the governance of urban public greenspace, and the challenges and opportunities for achieving the Sustainable Development Goals (SDGs) in the context of the Global South. The thesis offers a new integrated framework to inform urban greenspace governance and policy practices, with particular reference to the sustainable development of cities in the Global South
A cable-driven neck rehabilitation robot for neural rehabilitation
No full textDropped head syndrome (DHS) is often seen in patients with neuromuscular or neurological disorders. DHS patients face severe difficulty in lifting, moving, and holding their heads. They are typically prescribed physical therapy to reduce pain and restore their neck mobility. This thesis focuses on designing, modelling, and experimental investigation of a cable-driven robot for neck rehabilitation. The proposed mechanism is novel in how cable-driven joints and power transmission are deployed for neck therapy to control the complete natural range of motion. Additionally, the performance of the proposed robot is verified in Patient-in-change and Robot-in-charge modes.
Initially, the first version of a cable-driven neck rehabilitation robot (called CaRNeck-I) was proposed; it is able to support the human neck for two degrees of freedom (DoFs) only. Then, the improved version of the cable-driven neck rehabilitation robot (CaRNeck-III) was designed to assist neck therapy in controlling the complete natural range of motion. In this thesis, first, the proposed mechanism is described in detail, and screw theory is applied to carry out mobility analysis and closed-chain kinematics analysis. Second, the Jacobian and structure matrices are derived for two modes: robot-in-charge and patient-in-charge. Third, simulation experiments are employed to analyse cable tensions in static and dynamic scenarios. Fourth, a prototype has been developed, including cable-driven actuation modules and a humanoid neck. Finally, experimental investigations are reported in the proposed robot's passive, resistive, and active modes.
The proposed CaRNeck robot can be a potential solution to remediate DHS. To the best of my knowledge, the CaRNeck-III rehabilitation robot is the first in the literature to study, train, assist, and support coordinated head-neck movements for a complete natural rotational range of motion
Silicon integrated multimode Optical Phased Array (OPA) for parallel beam steering
No full textSilicon integrated Optical Phased Arrays (OPA) have been widely studied for wide and accurate beam steering applications, taking advantage of the high power handling capability, the stable and precise optical beam control, and the CMOS fabrication compatibility to realize low-cost devices. Both one-dimensional and two-dimensional silicon integrated OPAs have been demonstrated, and beam steering over a large angular range with versatile beam patterns have been achieved. However, existing silicon integrated OPAs are based on single mode operation, tuning the phase delay of the fundamental mode amongst phased array elements and generating a single beam from each OPA. Whilst generating more beams for parallel steering are feasible by using multiple OPAs integrated on the same silicon circuit, the device size, complexity as well as power consumption increase substantially. To overcome these limitations, in this research, we propose and demonstrate the feasibility of designing and using multimode OPA to generate more than one beam from the same silicon integrated OPA that can be steered in different locations to scan the target area in a parallel manner. The overall architecture, multiple beam parallel steering operation principle, and key individual components are designed and discussed. Results show that with the simplest two modes operation, the proposed multimode OPA design principle can realize parallel beam steering to reduce the total number of beam steering required over the target angular range and the power consumption by almost 50%, whilst minimizing the device size by more than 30%. When the multimode OPA operates with a larger number of modes, a larger number of beams can be generated, and the required total number of beam steering, the power consumption, and the size are further improved.
In addition, we have investigated key multimode supported components (e.g., mode multiplexer and converter, phase shifter, and emitter) required for the multimode OPA to achieve parallel beam steering. We have proposed a novel mode multiplexer and converter (MUX-C), one of the key components of the multimode OPA, based on asymmetric adiabatic taper approach, which has a low insertion loss of 0.32 dB and a broad bandwidth of 75 nm with a compact size. Besides, the proposed multimode phase shifter is capable of providing different phase shifts to signals with different modes. It achieves up to π phase shift for the TE0 and TE1 modes, consuming 25 mW and 23.7 mW power, respectively. It achieves a low thermal crosstalk of <-25 dB at a lateral distance of 21 µm. Besides, the designed multimode emitter can steer two different beams in two directions, forming parallel beam steering. The designed 1×4 emitter array with 1 μm element spacing and 0˚-150˚ phase delay can steer TE0 mode at 12˚and TE1 mode at 30˚ with negligible sidelobes and having a compact die area of 5.8 × 320 μm2. Therefore, all the designed multimode components contribute greatly to achieve the parallel beam steering with the improved performance of the proposed multimode OPA