arXiv subjects

Sendy Phang

Publications and source records attributed to Sendy Phang.

At least 19 recordsLinked to original sources

arXiv2026

Investigating reservoir computing for branch prediction in pipelined processors using emerging CMOS memristor devices

This project aimed to develop a novel reservoir compute (RC) implementation framework targeting high-speed operation and integration with CMOS digital logic. With the target workload of branch prediction (BP) for multistage pipelined central pro-cessing unit (CPU) cores. For this, a novel memristor based RC design framework was developed within the context of the workload requirements. This was then implemented in simulation using industry standard modelling languages of System Verilog (SV) and Verilog-AMS (VAMS).The developed RC design framework was subsequently verified using a basic sequence detection task before further benchmarking for its effectiveness at BP. The developed RC framework was tested using the Dhrystone performance benchmark, while targeting the RISC-V RV64GC instruction set architecture (ISA). Conducted testing demonstrates that RC shows great promise for ap-plication to BP and is capable of achieving impressive overall prediction accuracy. However, testing also shows that further refinement of the developed RC design framework is necessary to address shortfalls in the adaptability of the proposed RC system. As comparison against the state of the art TAGE predictor showed the proposed RC design framework to be 15x slower to adapt to changes in branching behaviour.

cs.AR↗

arXiv2026

Metasurface Tape for Efficient Millimeter-Wave Power Transfer via Surface-Wave Propagation

Millimeter-wave technologies are essential for future high-speed wireless communications. However, a fundamental challenge remains in the form of severe free-space path loss, where the power density decreases inversely with the square of the distance r (i.e., proportional to r^{-2}) as a spherical dependence. To overcome this limitation, we propose a flexible metasurface tape that is designed to guide electromagnetic energy as surface waves. Unlike conventional free-space propagation, this engineered metasurface confines the field to a subwavelength interface, thereby altering the power decay law to a circular dependence (i.e., proportional to r^{-1}). We numerically and experimentally, for the first time, demonstrate this concept using a periodic grounded-patch array fabricated on a flexible substrate and operated at approximately 100 GHz. The measurement results show that the metasurface tape significantly increases the transmitted power, yielding an average rate of improvement of approximately 40 per meter in received power relative to the free-space baseline in our measurement geometry (e.g., 29-dB increase at 2 m). This increase is realized over a broad bandwidth from 95 GHz to 105 GHz (i.e., approximately 10 %), accommodating wideband modulation schemes required for high-data-rate applications. The flexible, lightweight nature of the tape allows it to be easily installed on diverse surfaces. Our demonstration indicates that the metasurface tape is a promising platform for extending the effective range of millimeter-wave systems, thus offering a robust solution to the path-loss bottleneck in next-generation wireless networks.

physics.app-ph↗

arXiv2025

Photonic Matrix Multiplication Circuit Based on Double Racetrack Resonator Building Blocks

This paper presents a novel design framework for photonic matrix multiplication based on programmable photonic integrated circuits using double racetrack (DRT) resonators as building blocks. Here, we analytically demonstrate that the transfer function of the DRT resonator building block resembles that conventional building blocks, such as directional couplers and MZI, making it suitable for building programmable circuits that handle complex matrix calculations. Using this new DRT resonators building block, a 3-by-3 photonic processor is implemented and validated through full-wave Finite Element Method (FEM) simulations, and scalability is further analysed using hybrid FEM-circuit modelling. Additionally, we implement a low-pass filter as a non-unitary system example, showcasing the flexibility of the approach. Results confirm high fidelity between simulated and analytical models, supporting the viability of DRT resonators for reconfigurable photonic circuits. We believe that the proposed DRT resonator building blocks have the potential to complement and integrate with other previously reported blocks, thereby enhancing the fidelity and expanding the application scope of programmable photonic integrated circuits, particularly for all-optical signal processing in communication systems and for integration within microwave photonics platforms targeting emerging telecommunications technologies.

physics.optics↗

arXiv2024

Photonic Circuit of Arbitrary Non-Unitary Systems

A design framework to implement non-unitary input-output operations to a practical unitary photonic integrated circuit is described. This is achieved by utilising the cosine-sine decomposition to recover the unitarity of the original operation. The recovered unitary operation is decomposed into fundamental unitary building blocks, forming a photonic integrated circuit network based on directional couplers and waveguide phase shifters. The individual building blocks are designed and optimised by three-dimensional full-wave simulations and scaled up using a circuit approach. The paper investigates the scalability and robustness of the design approach. Our study demonstrates that the proposed approach of performing unitary matrix completion can be applied to any arbitrary matrices. This design approach allows for implementation of non-unitary operations to perform various linear functions in neuromorphic photonics for computing, sensing, signal processing and communications.

physics.optics↗

arXiv2024

An experimental demonstration of neuromorphic sensing of chemical species using electro-optical reservoir computing

A chemical discrimination system based on photonic reservoir computing is demonstrated experimentally for the first time. The system is inspired by the way humans perceive and process visual sensory information. The electro-optical reservoir computing system is a photonic analogue of the human nervous system with the read-out layer acting as the 'brain', and the sensor that of the human eye. A task-specific optimisation of the system is implemented, and the performance of the system for the discrimination between three chemicals is presented. The results are compared to the previously published numerical simulation. This publication provides a feasibility assessment and a demonstration of a practical realisation of photonic reservoir computing for a new neuromorphic sensing system - the next generation sensor with a built-in 'intelligence' which can be trained to 'understand' and to make a real time sensing decision based on the training data.

physics.optics↗

arXiv2024

New Reservoir Computing Kernel Based on Chaotic Chua Circuit and Investigating Application to Post-Quantum Cryptography

The aim of this project was to develop a new Reservoir Computer implementation, based on a chaotic Chua circuit. In addition to suitable classification and regression benchmarks, the Reservoir Computer was applied to Post-Quantum Cryptography, with its suitability for this application investigated and assessed. The cryptographic algorithm utilised was the Learning with Errors problem, for both encryption and decryption. To achieve this, the Chua circuit was characterised, in simulation, and by physical circuit testing. The Reservoir Computer was designed and implemented using the results of the characterisation. As part of this development, noise was considered and mitigated. The benchmarks demonstrate that the Reservoir Computer can achieve current literature benchmarks with low error. However, the results with Learning with Errors suggest that a Chua-based Reservoir Computer is not sufficiently complex to tackle the high non-linearity in Post-Quantum Cryptography. Future work would involve researching the use of different combinations of multiple Chua Reservoir Computers in larger neural network architectures. Such architectures may produce the required high-dimensional behaviour to achieve the Learning with Errors problem. This project is believed to be only the second instance of a Chua-based Reservoir Computer in academia, and it is the first to be applied to challenging real-world tasks such as Post-Quantum Cryptography. It is also original by its investigation of hitherto unexplored parameters, and their impact on performance. It demonstrates a proof-of-concept for a mass-producible, inexpensive, low-power consumption hardware neural network. It also enables the next stages in research to occur, paving the road for using Chua-based Reservoir Computers across various applications.

cs.CR↗

arXiv2023

SARIS: Scattering Aware Reconfigurable Intelligent Surface model and Optimization for Complex Propagation Channels

The reconfigurable intelligent surface (RIS) is an emerging technology that changes how wireless networks are perceived, therefore its potential benefits and applications are currently under intense research and investigation. In this letter, we focus on electromagnetically consistent models for RISs inheriting from a recently proposed model based on mutually coupled loaded wire dipoles. While existing related research focuses on free-space wireless channels thereby ignoring interactions between RIS and scattering objects present in the propagation environment, we introduce an RIS-aided channel model that is applicable to more realistic scenarios, where the scattering objects are modeled as loaded wire dipoles. By adjusting the parameters of the wire dipoles, the properties of general natural and engineered material objects can be modeled. Based on this model, we introduce a provably convergent and efficient iterative algorithm that jointly optimizes the RIS and transmitter configurations to maximize the system sum-rate. Extensive numerical results show the net performance improvement provided by the proposed method compared with existing optimization algorithms.

cs.IT↗

arXiv2023

Photonic reservoir computing enabled by stimulated Brillouin scattering

Artificial Intelligence (AI) drives the creation of future technologies that disrupt the way humans live and work, creating new solutions that change the way we approach tasks and activities, but it requires a lot of data processing, large amounts of data transfer, and computing speed. It has led to a growing interest of research in developing a new type of computing platform which is inspired by the architecture of the brain specifically those that exploit the benefits offered by photonic technologies, fast, low-power, and larger bandwidth. Here, a new computing platform based on the photonic reservoir computing architecture exploiting the non-linear wave-optical dynamics of the stimulated Brillouin scattering is reported. The kernel of the new photonic reservoir computing system is constructed of an entirely passive optical system. Moreover, it is readily suited for use in conjunction with high performance optical multiplexing techniques to enable real-time artificial intelligence. Here, a methodology to optimise the operational condition of the new photonic reservoir computing is described which is found to be strongly dependent on the dynamics of the stimulated Brillouin scattering system. The new architecture described here offers a new way of realising AI-hardware which highlight the application of photonics for AI.

physics.optics↗

arXiv2022

Electromagnetic Illusion in Smart Environments

Metasurfaces can be designed to achieve prescribed functionality. Careful meta-atom design and arrangement achieve homogeneous and inhomogeneous layouts that can enable exceptional capabilities to manipulate incident waves. Inherently, the control of scattering waves is crucial in wireless communications and stealth technologies. Low-profile and light-weight coatings that offer comprehensive manipulation are highly desirable for applications including camouflaging, deceptive sensing, radar cognition control, and defense security. Here, we propose a method that achieves electromagnetic illusion without altering the object. A proof of principle is proposed and practiced for one-dimensional media. The idea is to engineer the environment instead of the object coating. This work paves the way for versatile designs that will improve electromagnetic security applications with the aid of smart environments.

physics.app-ph↗

arXiv2022

Non-spectroscopic sensing enabled by electro-optical reservoir computer

A fully bio-inspired apparatus to perform non-spectroscopic sensing to discriminate, and determine the constituent concentrations of a chemical mixture is proposed. Here, fully bio-inspired means that it is comprised of a biomimetic sensor and a neuromorphic signal processor. The sensor is similar to the human eye in terms of its trichromat architecture and overlapping spectral response. The information processor is a neuromorphic system based on an electro-optical implementation of a reservoir computer. A time-stepping signal algorithm based on the Z-bilinear transformation has been developed to realistically simulate the electro-optical reservoir computer; this demonstrates the discrimination and chemical concentration determination tasks. We believe such an apparatus offers potential benefits in areas in which chemical composition needs to be monitored in real time, for example in chemical processing, and food-beverage (fermentation/brewing) and environmental monitoring.

physics.optics↗

arXiv2021

Smart Radio Environments

This Roadmap takes the reader on a journey through the research in electromagnetic wave propagation control via reconfigurable intelligent surfaces. Meta-surface modelling and design methods are reviewed along with physical realisation techniques. Several wireless applications are discussed, including beam-forming, focusing, imaging, localisation, and sensing, some rooted in novel architectures for future mobile communications networks towards 6G.

physics.class-ph↗

arXiv2021

Wireless Environment as a Service Enabled by Reconfigurable Intelligent Surfaces: The RISE-6G Perspective

The design of 6th Generation (6G) wireless networks points towards flexible connect-and-compute technologies capable to support innovative services and use cases. Targeting the 2030 horizon, 6G networks are poised to pave the way for sustainable human-centered smart societies and vertical industries, such that wireless networks will be transformed into a distributed smart connectivity infrastructure, where new terminal types are embedded in the daily environment. In this context, the RISE-6G project aims at investigating innovative solutions that capitalize on the latest advances in the emerging technology of Reconfigurable Intelligent Surfaces (RISs), which offers dynamic and goal-oriented radio wave propagation control, enabling the concept of the wireless environment as a service. The project will focus on: i) the realistic modeling of RIS-assisted signal propagation, ii) the investigation of the fundamental limits of RIS-empowered wireless communications and sensing, and iii) the design of efficient algorithms for orchestrating networking RISs, in order to implement intelligent, sustainable, and dynamically programmable wireless environments enabling diverse services that go well beyond the 5G capabilities. RISE-6G will offer two unprecedented proof-of-concepts for realizing controlled wireless environments in near-future use cases.

cs.IT↗

arXiv2020

Pseudo-Waveform-Selective Metasurfaces and Their Limited Performance

In recent years, metasurfaces composed of lumped circuit components, including nonlinear Schottky diodes, have been reported to be capable of sensing particular electromagnetic waves even at the same frequency depending on their waveforms, or more specifically, their pulse widths. In this study, we report analogous waveform-selective phenomena using only linear circuits and linear media. Although such linear metasurfaces are analytically and numerically demonstrated to exhibit variable absorption performance, it cannot strictly be categorized as waveform-selective absorption. It is due to the fact that the waveform-selective responses in the linear metasurfaces are originated from the dispersion behaviors of the structures rather than the frequency-conversion seen in nonlinear waveform-selective metasurfaces. We thus refer to these linear structures as pseudo-waveform-selective metasurfaces. Additionally, we show that the pseudo-waveform-selective metasurfaces have limited performance unless nonlinearity is introduced. These results and findings confirm the advantages of nonlinear waveform-selective metasurfaces, which can be exploited to provide an additional degree of freedom to address existing electromagnetic problems/challenges involving even waves at the same frequency.

physics.app-ph↗

arXiv2020

Efficient Statistical Model for Predicting Electromagnetic Wave Distribution in Coupled Enclosures

The Random Coupling Model (RCM) has been successfully applied to predicting the statistics of currents and voltages at ports in complex electromagnetic (EM) enclosures operating in the short wavelength limit. Recent studies have extended the RCM to systems of multi-mode aperture-coupled enclosures. However, as the size (as measured in wavelengths) of a coupling aperture grows, the coupling matrix used in the RCM increases as well, and the computation becomes more complex and time-consuming. A simple Power Balance Model (PWB) can provide fast predictions for the \textit{averaged} power density of waves inside electrically-large systems for a wide range of cavity and coupling scenarios. However, the important interference induced fluctuations of the wavefield retained in the RCM is absent in PWB. Here we aim to combine the best aspects of each model to create a hybrid treatment and study the EM fields in coupled enclosure systems. The proposed hybrid approach provides both mean and fluctuation information of the EM fields without the full computational complexity of coupled-cavity RCM. We compare the hybrid model predictions with experiments on linear cascades of over-moded cavities. We find good agreement over a set of different loss parameters and for different coupling strengths between cavities. The range of validity and applicability of the hybrid method are tested and discussed.

physics.class-ph↗

arXiv2020

Wireless Power Distributions in Multi-Cavity Systems at High Frequencies

The next generations of wireless networks will work in frequency bands ranging from sub-6 GHz up to 100 GHz. Radio signal propagation differs here in several critical aspects from the behaviour in the microwave frequencies currently used. With wavelengths in the millimeter range (mmWave), both penetration loss and free-space path loss increase, while specular reflection will dominate over diffraction as an important propagation channel. Thus, current channel model protocols used for the generation of mobile networks and based on statistical parameter distributions obtained from measurements become insufficient due to the lack of deterministic information about the surroundings of the base station and the receiver-devices. These challenges call for new modelling tools for channel modelling which work in the short wavelength/high-frequency limit and incorporate site-specific details -- both indoors and outdoors. Typical high-frequency tools used in this context -- besides purely statistical approaches -- are based on ray-tracing techniques. Ray-tracing can become challenging when multiple reflections dominate. In this context, mesh-based energy flow methods have become popular in recent years. In this study, we compare the two approaches both in terms of accuracy and efficiency and benchmark them against traditional power balance methods.

eess.SP↗

arXiv2018

Theory and Numerical Modelling of Parity-Time Symmetric Structures in Photonics: Boundary Integral Equation for Coupled Microresonator Structures

The spectral behaviour and the real-time operation of Parity-Time (PT PT) symmetric coupled resonators are investigated. A Boundary Integral Equation (BIE) model is developed to study these structures in the frequency domain. The impact of realistic gain/loss material properties on the operation of the PT PT-symmetric coupled resonators is also investigated using the time-domain Transmission-Line Modelling (TLM) method. The BIE method is also used to study the behaviour of an array of PT-microresonator photonic molecules.

physics.optics↗

arXiv2018

Theory and Numerical Modelling of Parity-Time Symmetric Structures in Photonics: Introduction and Grating Structures in One Dimension

A class of structures based on PT PT-symmetric Bragg gratings in the presence of both gain and loss is studied. The basic concepts and properties of parity and time reversal in one-dimensional structures that possess idealised material properties are given. The impact of realistic material properties on the behaviour of these devices is then investigated. Further extension to include material non-linearity is used to study an innovative all-optical memory device.

physics.optics↗

arXiv2015

Localized Single Frequency Lasing States in a Finite Parity-Time Symmetric Resonator Chain

In this paper a practical case of a finite periodic Parity Time chain made of resonant dielectric cylinders is considered. The paper analyzes a more general case where PT symmetry is achieved by modulating both the real and imaginary part of the material refractive index along the resonator chain. The band-structure of the finite periodic PT resonator chains is compared to infinite chains in order to understand the complex interdependence of the Bloch phase and the amount of the gain/loss in the system that causes the PT symmetry to break. The results show that the type of the modulation along the unit cell can significantly affect the position of the threshold point of the PT system. In all cases the lowest threshold is achieved near the end of the Brillouin zone. In the case of finite PT-chains, and for a particular type of modulation, early PT symmetry breaking is observed and shown to be caused by the presence of termination states localized at the edges of the finite chain resulting in localized lasing and dissipative modes at each end of the chain.

physics.optics↗