1,191 research outputs found

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Pulsed Free Space Photonic Vector Network Analyzers

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    Terahertz (THz) radiation (0.1–10 THz) has demonstrated great significance in a wide range of interdisciplinary applications due to its unique properties such as the capacity to penetrate optically opaque materials without ionizing effect, superior spatial resolution as compared to the microwave domain for imaging or ability to identify a vast array of molecules using THz fingerprinting. Advancements in generation and detection techniques, as well as the necessities of application-driven research and industry, have created a substantial demand for THz-range devices and components. However, progress in the development of THz components is hampered by a lack of efficient and affordable characterization systems, resulting in limited development in THz science and technology. Vector Network Analyzers (VNAs) are highly sophisticated well-established characterization instruments in the microwave bands, which are now employed in the lower end of the THz spectrum (up to 1.5 THz) using frequency extender modules. These modules are extremely expensive, and due to the implementation of hollow metallic waveguides for their configuration, they are narrowband, requiring at least six modules to achieve a frequency coverage of 0.2–1.5 THz. Moreover, they are susceptible to problems like material losses, manufacturing and alignment tolerances etc., making them less than ideal for fast, broadband investigation. The main objective of this thesis is to design a robust but cost-effective characterization system based on a photonic method that can characterize THz components up to several THz in a single configuration. To achieve this, we design architectures for the Photonic Vector Network Analyzer (PVNA) concept, incorporating ErAs:In(Al)GaAs-based photoconductive sources and ErAs:InGaAs-based photoconductive receivers, driven with a femtosecond pulsed laser operating at 1550 nm. The broadband photonic devices replace narrowband electronic ones in order to record the Scattering (S)-parameters in a free space configuration. Corresponding calibration and data evaluation methods are also developed. Then the PVNAs are configured, and their capabilities are validated by characterizing various THz components, including a THz isolator, a distributed Bragg Reflector, a Split-Ring Resonator array and a Crossed-Dipole Resonator (CDR) array, in terms of their S-parameters. The PVNAs are also implemented to determine the complex refractive index or dielectric permittivity and physical thickness of several materials in the THz range. Finally, we develop an ErAs:In(Al)GaAs-based THz transceiver and implement it in a PVNA configuration, resulting in a more compact setup that is useful for industrial applications. The feasibility of such systems is also verified by characterizing several THz components. The configured systems achieve a bandwidth of more than 2.5 THz, exceeding the maximum attainable frequency of the commercial Electronic Vector Network Analyzer (EVNA) extender modules. For the 1.1-1.5 THz band, the dynamic range of 47-35 dB (Equivalent Noise Bandwidth (ENBW) = 9.196 Hz) achieved with the PVNA is comparable to the dynamic range of 45-25 dB (ENBW = 10 Hz) of the EVNA. Both amplitude and phase of the S-parameters, determined by the configured PVNAs, are compared with simulations or theoretical models and showed excellent agreement. The PVNA could discern multi-peak and narrow resonance characteristics despite its lower spectral resolution (∼3-7 GHz) compared to the EVNA. By accurately determining the S-parameters of multiple THz components, the transceiver-based PVNA also demonstrated its exceptional competence. With huge bandwidth and simpler calibration techniques, the PVNA provides a potential solution to bridge the existing technological gap in THz-range characterization systems and offers a solid platform for THz component development, paving the way for more widespread application of THz technologies in research and industry

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    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

    Sensing Collectives: Aesthetic and Political Practices Intertwined

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    Are aesthetics and politics really two different things? The book takes a new look at how they intertwine, by turning from theory to practice. Case studies trace how sensory experiences are created and how collective interests are shaped. They investigate how aesthetics and politics are entangled, both in building and disrupting collective orders, in governance and innovation. This ranges from populist rallies and artistic activism over alternative lifestyles and consumer culture to corporate PR and governmental policies. Authors are academics and artists. The result is a new mapping of the intermingling and co-constitution of aesthetics and politics in engagements with collective orders

    Analog Photonics Computing for Information Processing, Inference and Optimisation

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    This review presents an overview of the current state-of-the-art in photonics computing, which leverages photons, photons coupled with matter, and optics-related technologies for effective and efficient computational purposes. It covers the history and development of photonics computing and modern analogue computing platforms and architectures, focusing on optimization tasks and neural network implementations. The authors examine special-purpose optimizers, mathematical descriptions of photonics optimizers, and their various interconnections. Disparate applications are discussed, including direct encoding, logistics, finance, phase retrieval, machine learning, neural networks, probabilistic graphical models, and image processing, among many others. The main directions of technological advancement and associated challenges in photonics computing are explored, along with an assessment of its efficiency. Finally, the paper discusses prospects and the field of optical quantum computing, providing insights into the potential applications of this technology.Comment: Invited submission by Journal of Advanced Quantum Technologies; accepted version 5/06/202

    Tools for efficient Deep Learning

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    In the era of Deep Learning (DL), there is a fast-growing demand for building and deploying Deep Neural Networks (DNNs) on various platforms. This thesis proposes five tools to address the challenges for designing DNNs that are efficient in time, in resources and in power consumption. We first present Aegis and SPGC to address the challenges in improving the memory efficiency of DL training and inference. Aegis makes mixed precision training (MPT) stabler by layer-wise gradient scaling. Empirical experiments show that Aegis can improve MPT accuracy by at most 4\%. SPGC focuses on structured pruning: replacing standard convolution with group convolution (GConv) to avoid irregular sparsity. SPGC formulates GConv pruning as a channel permutation problem and proposes a novel heuristic polynomial-time algorithm. Common DNNs pruned by SPGC have maximally 1\% higher accuracy than prior work. This thesis also addresses the challenges lying in the gap between DNN descriptions and executables by Polygeist for software and POLSCA for hardware. Many novel techniques, e.g. statement splitting and memory partitioning, are explored and used to expand polyhedral optimisation. Polygeist can speed up software execution in sequential and parallel by 2.53 and 9.47 times on Polybench/C. POLSCA achieves 1.5 times speedup over hardware designs directly generated from high-level synthesis on Polybench/C. Moreover, this thesis presents Deacon, a framework that generates FPGA-based DNN accelerators of streaming architectures with advanced pipelining techniques to address the challenges from heterogeneous convolution and residual connections. Deacon provides fine-grained pipelining, graph-level optimisation, and heuristic exploration by graph colouring. Compared with prior designs, Deacon shows resource/power consumption efficiency improvement of 1.2x/3.5x for MobileNets and 1.0x/2.8x for SqueezeNets. All these tools are open source, some of which have already gained public engagement. We believe they can make efficient deep learning applications easier to build and deploy.Open Acces

    Design and characterisation of monolithic CMOS detectors for high energy particle physics and SEU radiation tests for ATLAS Inner Tracker Upgrade readout chip

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    This thesis covers the characterisation results and the design of monolithic CMOS detectors designed in TowerJazz 180nm CMOS technology for High Energy Particle Physics applications. Three different detectors have been studied the MALTA, the Mini-MALTA and the MALTA2. The MALTA sensor showed some efficiency losses at the corners of the pixels after irradiation, which meant that it was not suitable for the radiation environments in which it was supposed to be installed. Therefore, the front-end electronics and the fabrication process were modified to overcome this issue. The Mini-MALTA prototype was designed including the above mentioned improvements, fabricated and fully characterised. Finally taking into account all the knowledge acquired during these years of developments another large scale sensor the MALTA2 has been produced which should be radiation tolerant and have very good time resolution. The description and studies of the different architectures used in this family of detectors are covered and a simulation to estimate the bandwidth capabilities have been reported. Furthermore, this work will present characterisation of single event effects in the ITkPixV1, the prototype version of the ATLAS Inner Tracker Upgrade chip for the High Luminosity LHC. Measurements were made in testbeam campaigns with high energy ions and protons to evaluate the level of single event effects in the chip

    Integrated Optical Receivers for High-speed Indoor Optical Wireless Communication

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    Stokes Vector Modulation of Optical Signals; Coherence, Noise, and Digital Signal Processing

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    Stokes vector modulation (SVM) is a method of encoding information onto an optical wave by controlling its amplitude and its state of polarization (SOP). SVM offers the potential to achieve the high spectral efficiency of multi-dimensional symbols using a power-efficient, direct-detection receiver. Combining the two independent degrees of freedom representing polarization with one representing amplitude, SVM symbols are defined in a 3-D space of Stokes vectors, where vector length represents the amplitude and altitude/azimuth angles represent the SOP. The recoverable information content is fundamentally limited by the noise on the received signal, which may include shot noise due to photon-counting, electrical circuit noise, amplified spontaneous emission due to optical amplifiers, and self-interference of low-coherence light sources. Some of these noise terms do not obey the usual approximation of additive white Gaussian noise, and some may not be isotropic in Stokes space. Taking these complexities into account, I will theoretically analyze and compare several recently-proposed SVM receiver designs under different conditions of source coherence and channel impairments. For the most promising options, I will design symbol constellations and receiver decision strategies suitable for maximal data throughput. Construction and operation of apparatus to experimentally verify bit-error performance up to at least 10 Gsym/s with different sources, constellations, fiber spans, and receivers will be an essential component of the work. Possible extensions may include simultaneous modulation of the degree of polarization, to create a 4-D symbol space. Further, I will develop and characterize a system based on a cubic constellation for 8-SVM, using an off-the-shelf integrated modulator driven with simple bias points and data waveforms. Symbol error rates (SER) and bit error rates BER) are measured up to 30 Gb/s, and analysis of the symbol errors reveals a significant effect of inter-symbol interference. Finally, I will theoretically and experimentally demonstrate a novel adaptation of independent component analysis (ICA) for compensation of both cross-polarization and inter-symbol interference in a direct-detection link using Stokes vector modulation (SVM). SVM systems suffer from multiple simultaneous impairments that can be difficult to resolve with conventional optical channel DSP techniques. The proposed method is based on a six-dimensional adaptation of ICA that simultaneously derotates the SVM constellation, corrects distortion of constellation shape, and mitigates inter-symbol interference (ISI) at high symbol rates. Experimental results at 7.5 Gb/s and 15Gb/s show that the newly-developed ICA-based equalizer achieves power penalties below ~1 dB, compared to the ideal theoretical bit-error rate (BER) curves. At 30-Gb/s, where ISI is more severe, ICA still enables polarization de-rotation and BE

    Forecasting the Past and Recalling the Future: Lemniscate Narratives in the Work of Richard Powers

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    Richard Powers’s multifaceted accounts of individuals navigating turbulent histories are relayed via nonlinear timelines, situating the future in relation to an imminent past. The characters’ reassembly of pre-existing compositions, patterns, and traditions in self-styled configurations, engages with interlocking legacies whilst asserting their individual perspective on reality. Multiple analyses of Powers’s texts have focused on the permeable borders between interconnected genres, eras, and disciplines in relation to spliced or stereoscopic images of society. The six texts analysed in this comparative study depict twofold timelines intersecting in the present, creating a lemniscate form with a seemingly endless course of expansion. This comparative approach assesses the converging and diverging lemniscate narrative form and content of six texts written at different stages in Powers’s career. The thesis explores the purpose of each text’s proposed lemniscate temporal frame in relation to the reoccurring depictions of transmedial utopian fictions and a neocolonial US history. This synthesis of pre-existing forms, modernist, and postmodernist world views resembles a metamodernist or transglossic literary style. The tensions between individual and hegemonic ideologies are explored within the three comparative chapters, evaluating the similarities and differences between Powers’s treatment of music and science, innovation and neocolonialism, and individual and collective responses to autonomy in the Atomic Age US
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