A5075509370- Neural Networks and Reservoir Computing
- Photonic and Optical Devices
- Advanced Memory and Neural Computing
- Semiconductor Quantum Structures and Devices
- Nanowire Synthesis and Applications
- Optical Network Technologies
- Neural dynamics and brain function
- GaN-based semiconductor devices and materials
- Perovskite Materials and Applications
- Graphene research and applications
- Optical properties and cooling technologies in crystalline materials
- Neural Networks and Applications
- Plasmonic and Surface Plasmon Research
- Ga2O3 and related materials
- Optical Coatings and Gratings
- ZnO doping and properties
- Quantum Dots Synthesis And Properties
- Solid-state spectroscopy and crystallography
- Image Processing Techniques and Applications
- CCD and CMOS Imaging Sensors
University of Manchester
2017-2023
Technical University of Denmark
2023
TU Wien
2023
Boston University
2023
University College Cork
2023
Shanghai Institute of Technical Physics
2023
University of Strathclyde
2021-2022
International Iberian Nanotechnology Laboratory
2022
University of Lisbon
2022
Photonics (United States)
2020
Abstract The ever-increasing demand for artificial intelligence (AI) systems is underlining a significant requirement new, AI-optimised hardware. Neuromorphic (brain-like) processors are one highly-promising solution, with photonic-enabled realizations receiving increasing attention. Among these, approaches based upon vertical cavity surface emitting lasers (VCSELs) attracting interest given their favourable attributes and mature technology. Here, we demonstrate hardware-friendly...
Driven by the increasing significance of artificial intelligence, field neuromorphic (brain-inspired) photonics is attracting interest, promising new, high-speed, and energy-efficient computing hardware for key applications in information processing computer vision. Widely available photonic devices, such as vertical-cavity surface emitting lasers (VCSELs), offer highly desirable properties implementations systems, high-speed low energy operation, neuron-like dynamical responses, ease...
In this work, we introduce an interconnected nano-optoelectronic spiking artificial neuron emitter-receiver system capable of operating at ultrafast rates (about $100\phantom{\rule{0.2em}{0ex}}\mathrm{ps}/$optical spike) and with low-energy consumption ( pJ/spike). The proposed combines excitable resonant tunneling diode (RTD) element exhibiting negative differential conductance, coupled to a nanoscale light source (forming master node) or photodetector receiver node). We study numerically...
Continuous room temperature nanowire lasing from silicon-integrated optoelectronic elements requires careful optimisation of both the cavity Q-factor and population inversion conditions. We apply time-gated optical interferometry to emission high-quality GaAsP/GaAs quantum well laser structures, revealing high Q-factors 1250 ± 90 corresponding end-facet reflectivities R = 0.73 0.02. By using optimised direct-indirect band alignment in active region, we demonstrate a well-refilling mechanism...
Single nanowire lasers based on bottom-up III-V materials have been shown to exhibit room-temperature near-infrared lasing, making them highly promising for use as nanoscale, silicon-integrable, and coherent light sources. While lasing behavior is reproducible, small variations in growth conditions across a substrate arising from the of techniques can introduce interwire disorder, either through geometric or material inhomogeneity. Nanolasers critically depend both high quality tight...
Fluence-dependent photoluminescence and ultrafast transient absorption spectroscopy are used to study the dynamic behavior of carriers in CsPbCl3 perovskite nanocrystals. At low excitation fluences, radiative recombination rate is outcompeted by significant trapping charge which then recombine nonradiatively, resulting weak photoluminescence. As fluence increased, saturation trap states deactivates these nonradiative relaxation paths giving rise an increase at first. However, with further...
Semiconductor nanowires suffer from significant non-radiative surface recombination; however, heavy p-type doping has proven to be a viable option increase the radiative recombination rate and, hence, quantum efficiency of emission, allowing demonstration room-temperature lasing. Using large-scale optical technique, we have studied Zn-doped GaAs understand and quantify effect on growth lasing properties. We measure (knr) (0.14 ± 0.04) ps–1 by modeling internal (IQE) as function level. By...
Semiconductor nanowire (NW) lasers are a promising technology for the realisation of coherent optical sources with extremely small footprint. To fully realize their potential as building blocks in on-chip photonic systems, scalable methods required dealing large populations inhomogeneous devices that typically randomly distributed on host substrates. In this work two complementary, high-throughput techniques combined: characterisation laser using automated microscopy, and high accuracy...
The internal quantum efficiency of (In,Ga)N/GaN wells can surpass 90% for blue-emitting structures at moderate drive current densities but decreases significantly longer emission wavelengths and higher excitation rates. This latter effect is known as "droop" limits the brightness light-emitting diodes (LEDs) based on such wells. Several mechanisms have been proposed to explain droop including Auger recombination, both intrinsic defect-assisted, carrier escape, saturation localized states....
In this paper, we report a high-speed and tunable photonic synaptic element based on vertical cavity semiconductor optical amplifier (VCSOA) operating with short (150 ps-long) low-energy (μW peak power) light pulses. By exploiting nonlinear gain properties of VCSOAs when subject to external injection, our system permits full weight tunability sub-ns input pulses, just by varying the VCSOA's applied bias current. Not only is VCSOA-based synapse able adjust strength incoming but it can also...
The design of efficient graphene-silicon (GSi) Schottky junction photodetectors requires detailed understanding the spatial origin photoresponse. Scanning-photocurrent-microscopy (SPM) studies have been carried out in visible wavelengths regions only, which response due to silicon is dominant. Here we present comparative SPM ( nm) and infrared wavelength for a number GSi photodetector architectures, revealing photoresponse mechanisms graphene dominated responses, respectively, demonstrating...
Both gain medium design and cavity geometry are known to be important for low threshold operation of semiconductor nanowire lasers. For many applications lasers need transferred from the growth substrate a low-index substrate; however, impact transfer process on optoelectronic performance has not been studied. Ultrasound, PDMS-assisted mechanical rubbing most commonly used methods transfer; each method may cause changes in fracture point which can potentially affect both length end-face...
We present a method to correlate multimodal measurements—namely optical spectroscopy and electron microscopy—over large ensembles of randomly distributed single nano-objects. Using an algorithmic approach derived from astrometry, marker-free uniquely associating nano-objects characterised using multiple techniques is described. This applied nanolasers, enabling experimental calculation modal refractive index in sub-micron diameter nanowires. By matching the lasing spectrum microscopy image...
Perovskite colloidal nanocrystals have emerged as important new optical materials, with tunable light emission across the visible spectrum, narrow line widths for high color purity, and quantum efficiencies approaching unity. These materials can be solution processed in large volumes at low cost making them promising optoelectronic devices. The structure of influences radiative nonradiative recombination carriers within through trap states Auger recombination. To optimize properties it is...
We report experimentally on high-speed, tuneable photonic synaptic architectures realized with vertical cavity surface emitting lasers (VCSELs) connected in series and parallel configurations. These are able to perform the controlled weighting of fast (150 ps long) low energy ( µ W peak power) optical pulses (or spikes), permit high-speed (0.5 GHz) dynamic weight tunability, for implementation important spike processing functionalities. include, in-series VCSEL architecture, performance...
Event-activated biological-inspired subwavelength (sub-λ) optical neural networks are of paramount importance for energy-efficient and high-bandwidth artificial intelligence (AI) systems.Despite the significant advances to build active neurons using example phase-change materials, lasers, photodetectors, modulators, miniaturized integrated sources detectors suited few-photon spike-based operation interest neuromorphic computing still lacking.In this invited paper we outline main challenges,...
III-V semiconductor nanowires allow easy hetero-integration of optoelectronic components onto silicon due to efficient strain relaxation, well-understood design approaches and scalability. However continuous room temperature lasing has proven elusive. A key challenge is performing repeatable <i>single-wire</i> characterization { each wire can be different local growth conditions present during bottom-up growth. Here, we describe an approach using large-scale population studies which exploit...
Abstract Micro-photoluminescence maps reveal micron-scale spatial variation in intensity, peak emission energy and bandwidth across InGaN/GaN quantum wells. To investigate the effect of this on measurements dependence efficiency carrier density, excitation power-dependent was collected from a bright dark region each blue-and green emitting samples. The onset droop found to occur at greater density regions than bright, by factors 1.2 1.8 blue green-emitting samples, respectively. By spatially...
We present a combined theoretical and experimental analysis of Auger recombination in c-plane (In,Ga)N quantum wells. On the side we use an atomistic model that accounts for random alloy fluctuations to investigate impact temperature carrier density has on radiative rate. Our calculations indicate weak dependence rate compared However, with increasing increases more strongly when theory results onset efficiency drop at densities ≳ 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML"...
The design of efficient graphene-silicon (GSi) Schottky junction photodetectors requires detailed understanding the spatial origin photoresponse. Scanning-photocurrent-microscopy (SPM) studies have been carried out in visible wavelengths regions only, which response due to silicon is dominant. Here we present comparative SPM ($\lambda$ = 633nm) and infrared 1550nm) wavelength for a number GSi photodetector architectures, revealing photoresponse mechanisms graphene dominated responses,...
We report high-speed, energy-efficient artificial optoelectronic spiking neurons based upon resonant tunnelling diodes (RTD). Using these, we demonstrate a photonic neural network (perceptron) numerical model for classification of spatiotemporal pulse patterns with 94% accuracy.
Pairs of interconnected brain-inspired photonic synapses (connected in-parallel and in-series) are developed using Vertical Cavity Surface Emitting Lasers (VCSELs). We discuss the operation each configuration demonstrate their capability to perform different spike-based processing tasks including information encoding, temporal filtering, Multiply-and-Accumulate (MAC) operations.