Next Generation Silicon Photonic Transceiver: From Device Innovation to System Analysis

Silicon photonics is recognized as a disruptive technology that has the potential to reshape many application areas, for example, data center communication, telecommunications, high-performance computing, and sensing. The key capability that silicon photonics offers is to leverage CMOS-style design, fabrication, and test infrastructure to build compact, energy-efficient, and high-performance integrated photonic systems-on- chip at low cost. As the need to squeeze more data into a given bandwidth and a given footprint increases, silicon photonics becomes more and more promising. This work develops and demonstrates novel devices, methodologies, and architectures to resolve the challenges facing the next-generation silicon photonic transceivers. The first part of this thesis focuses on the topology optimization of passive silicon photonic devices. Specifically, a novel device optimization methodology - particle swarm optimization in conjunction with 3D finite-difference time-domain (FDTD), has been proposed and proven to be an effective way to design a wide range of passive silicon photonic devices. We demonstrate a polarization rotator and a 90◦ optical hybrid for polarization-diversity and phase-diversity communications - two important schemes to increase the communication capacity by increasing the spectral efficiency. The second part of this thesis focuses on the design and characterization of the next- generation silicon photonic transceivers. We demonstrate a polarization-insensitive WDM receiver with an aggregate data rate of 160 Gb/s. This receiver adopts a novel architecture which effectively reduces the polarization-dependent loss. In addition, we demonstrate a III-V/silicon hybrid external cavity laser with a tuning range larger than 60 nm in the C-band on a silicon-on-insulator platform. A III-V semiconductor gain chip is hybridized into the silicon chip by edge-coupling to the silicon chip. The demonstrated packaging method requires only passive alignment and is thus suitable for high-volume production. We also demonstrate all silicon-photonics-based transmission of 34 Gbaud (272 Gb/s) dual-polarization 16-QAM using our integrated laser and silicon photonic coherent transceiver. The results show no additional penalty compared to commercially available narrow linewidth tunable lasers. The last part of this thesis focuses on the chip-scale optical interconnect and presents two different types of reconfigurable memory interconnects for multi-core many-memory computing systems. These reconfigurable interconnects can effectively alleviate the memory access issues, such as non-uniform memory access, and Network-on-Chip (NoC) hot-spots that plague the many-memory computing systems by dynamically directing the available memory bandwidth to the required memory interface

The Role of Soil Indigenous Microbes and Their Interactions with Maize Plants in Arsenic Uptake, Translocation, Speciation and Detoxification in the Soil-Plant System

Arsenic (As) is a metalloid that is classified as a Class 1 carcinogen. Due to its high toxicity, As can cause a variety of human diseases such as anemia, leucopenia, and skin cancer. Arsenic is persistent, non-biodegradable, and bio-accumulative, and it persists in soils for extended periods of time and has negative effects on soil organisms. Since As is readily absorbed by plants, it can harm crop plants and result in a reduction in crop development and yields. Once these plants are consumed by animals or humans, As can enter the human food chain and poses a serious health risk to both animals and humans. To avoid such harmful repercussions, it is necessary to understand the uptake, translocation, speciation, and detoxification of As in the systemic soil-plant system. The overall goal of my research is to investigate the role of soil indigenous microbes to immobilize As in soils and decrease its bioavailability to plants. Specifically, there are three questions to be answered: (i) What are the effects of microbial disturbance, plant growth, and As treatments on the concentration and speciation of As in soil water and in soils? (ii) How do microbial disturbance and As treatments affect the concentration and speciation of As in maize (Zea mays L.) plants? And (iii) what effects do microbial disturbance and As treatments have on the health of maize plants? To answer these research questions, a greenhouse pot experiment was conducted to investigate the transformation of As in the soil-maize system and its influence on plant health. Three soil treatments with varying levels of soil microbial disturbance were performed in the experiment: native soil (NS, control soils), reconditioned soil (RS, sterilized soils and reconditioned with native soil microbes), and disturbed soil (DS, sterilized soil before planting). The DS and RS treatments were introduced to differentiate between biotic (microbial disturbance) and abiotic (soil sterilization) effects. The sterilization effect was the same in DS and RS, while the microbial disturbance effect was partly eliminated in the RS treatment due to the microbial reconditioning. Therefore, it is assumed that the difference between RS and DS showed the microbial disturbance effect, and the difference between NS and RS reflected the abiotic effect. The three soil treatments were intersected with three As treatments (uncontaminated soils (As0), moderate-As soils (As100, addition of 100 mg As kg−1 soil), and high-As soils (As200, addition of 200 mg As kg−1soil)). There were three replicates without maize (No-plant) and ten replicates with maize (Plant). This experiment thus comprised a total of 18 treatment groups. Arsenic concentration and speciation were analyzed in soil water, in soils, and in different maize tissues (roots, stem, leaves, and grains). Arsenic speciation was categorized into inorganic As species (inAs, i.e., arsenate (AsV) and arsenite (AsIII)) and organic As species (orgAs, including methylarsonic acid (MMAV), dimethylarsinic acid (DMAV), and trimethylarsine oxide (TMAO)). Various plant health parameters were also measured on a regular basis to examine the physiological responses of maize to microbial disturbance and As exposure, including plant height, fresh and dry biomass, BBCH-scale, leaf numbers per plant, leaf chlorophyll content, and damage scale of leaf spot. In soil water, total As (totAs) and As species followed a general concentration pattern of NS < RS ≤ DS, owing to the release of As into soil water caused by both the microbial disturbance and sterilization effects. Both effects played a greater role in the concentration of orgAs compared to that of inAs in soil water, implying that microbial disturbance may have influenced the methylation process of As, which converts inAs to organic forms. The microbial disturbance effect (difference RS-DS) is defined as the difference between RS and DS and is caused by the presence of soil indigenous microbes in RS. While the sterilization effect (difference NS-RS) is due to physicochemical changes and nutrient release after soil sterilization. For instance, the increased concentration of dissolved organic carbon (DOC) in soil water and lowered soil pH could mobilize As in soil water. Interestingly, the presence of maize plants mitigated both the microbial disturbance and sterilization effects, possibly helping soil microbes to recover from soil sterilization and favoring beneficial microbes in coping with As stress jointly (Chapter II). The concentrations of totAs and inAs in maize tissues followed the same order of NS leaves > stem > grains in uncontaminated soils, while in contaminated soils, the position of stem and leaves changed, indicating lower translocation of As into the maize leaves and grains. Moreover, the simultaneous presence of microbial disturbance and sterilization effects could exaggerate the adverse effects of As on plant health. Without added As (As0), both effects had no effect on dry biomass, which is one of the most critical indicators of plant growth and health. In the presence of As, however, the loss in dry biomass was more pronounced in maize grown in sterilized soils (RS and DS) than in unsterilized soils (NS) due to the sterilization effect. Furthermore, inAs and MMAV were revealed to be the species responsible for the loss in dry biomass, probably due to the high abundance and toxicity of inAs and the efficient translocation of MMA in maize (Chapter III). As with dry biomass, plant height and BBCH-scale were not affected by both the microbial disturbance and sterilization effects in maize grown on uncontaminated soils, implying that plants are capable to buffer both effects. In contrast, the effects of microbial disturbance on contaminated soils resulted in a reduction in plant height, leaf numbers, and chlorophyll content as well as an increase in the damage scale of leaf spot. Even at a high As concentration in soils, these affected health parameters were not or only slightly retarded in maize in NS indicating the resilience of an undisturbed soil-microbe-plant system. The sterilization effect caused phosphorus (P) and manganese (Mn) deficiencies in maize grown on high-As soils, which hampered plant growth and may have indirectly led to increased As accumulation in maize plants (Chapter IV). Overall, this research highlights the importance of soil indigenous microbes and their potential interaction with plants in their common resistance to the detrimental effects of As, which may improve the knowledge of As uptake, translocation, speciation, and detoxification in the soil-maize system and reduce As inputs into the food chain. This could also help to ensure food safety, food security, and sustainable food production as well as the protection of animal and human health. Further studies on soil microbial diversity, communities, and functioning (e.g., enzyme activity) as well as plant microbial communities, would be beneficial to learn more about As effects on soil health and plant health

Novel polarization-diversity devices on a silicon-on-insulator platform.

Master'sMASTER OF ENGINEERIN

Reversible Watermarking in Deep Convolutional Neural Networks for Integrity Authentication

Deep convolutional neural networks have made outstanding contributions in many fields such as computer vision in the past few years and many researchers published well-trained network for downloading. But recent studies have shown serious concerns about integrity due to model-reuse attacks and backdoor attacks. In order to protect these open-source networks, many algorithms have been proposed such as watermarking. However, these existing algorithms modify the contents of the network permanently and are not suitable for integrity authentication. In this paper, we propose a reversible watermarking algorithm for integrity authentication. Specifically, we present the reversible watermarking problem of deep convolutional neural networks and utilize the pruning theory of model compression technology to construct a host sequence used for embedding watermarking information by histogram shift. As shown in the experiments, the influence of embedding reversible watermarking on the classification performance is less than 0.5% and the parameters of the model can be fully recovered after extracting the watermarking. At the same time, the integrity of the model can be verified by applying the reversible watermarking: if the model is modified illegally, the authentication information generated by original model will be absolutely different from the extracted watermarking information.Comment: Accepted to ACM MM 202

Document Clustering Method Based on Frequent Co-occurring Words

PACLIC 20 / Wuhan, China / 1-3 November, 200

Application of the robust estimate in SLR data preprocessing

An M-estimator, one kind of a robust estimator, has been used in satellite laser ranging (SLR) data preprocessing. It has been shown that the M-estimator has a 50 percent or more breakdown point

A Cooperative Deception Strategy for Covert Communication in Presence of a Multi-antenna Adversary

Covert transmission is investigated for a cooperative deception strategy, where a cooperative jammer (Jammer) tries to attract a multi-antenna adversary (Willie) and degrade the adversary's reception ability for the signal from a transmitter (Alice). For this strategy, we formulate an optimization problem to maximize the covert rate when three different types of channel state information (CSI) are available. The total power is optimally allocated between Alice and Jammer subject to Kullback-Leibler (KL) divergence constraint. Different from the existing literature, in our proposed strategy, we also determine the optimal transmission power at the jammer when Alice is silent, while existing works always assume that the jammer's power is fixed. Specifically, we apply the S-procedure to convert infinite constraints into linear-matrix-inequalities (LMI) constraints. When statistical CSI at Willie is available, we convert double integration to single integration using asymptotic approximation and substitution method. In addition, the transmission strategy without jammer deception is studied as a benchmark. Finally, our simulation results show that for the proposed strategy, the covert rate is increased with the number of antennas at Willie. Moreover, compared to the benchmark, our proposed strategy is more robust in face of imperfect CSI.Comment: 33 pages, 8 Figure