School of Physics - Research Publications
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ItemNo Preview AvailableTunable nonlocal metasurfaces based on graphene for analogue optical computation(Optica Publishing Group, 2023-05-01)Meta-optical devices have recently emerged as ultra-compact candidates for real-time computation in the spatial domain. The use of meta-optics for applications in image processing and wavefront sensing could enable an order of magnitude increase in processing speed and data throughput, while simultaneously drastically reducing the footprint of currently available solutions to enable miniaturisation. Most research to date has focused on static devices that can perform a single operation. Dynamically tunable devices, however, offer increased versatility. Here we propose graphene covered subwavelength silicon carbide gratings as electrically tunable optical computation and image processing devices at mid-infrared wavelengths.
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ItemThin film notch filters as platforms for biological image processing(NATURE PORTFOLIO, 2023-03-18)Many image processing operations involve the modification of the spatial frequency content of images. Here we demonstrate object-plane spatial frequency filtering utilizing the angular sensitivity of a commercial spectral bandstop filter. This approach to all-optical image processing is shown to generate real-time pseudo-3D images of transparent biological and other samples, such as human cervical cancer cells. This work demonstrates the potential of non-local, non-interferometric approaches to image processing for uses in label-free biological cell imaging and dynamical monitoring.
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ItemReal-Time Phase Imaging with an Asymmetric Transfer Function Metasurface(AMER CHEMICAL SOC, 2022-05-18)The conversion of phase variations in an optical wavefield into intensity information is of fundamental importance for optical imaging including the microscopy of biological cells. Recently, meta-optical devices have demonstrated all-optical, ultracompact image processing of optical wavefields but are limited by their symmetric optical response to amplitude and phase gradients. Here, we describe a metasurface that exploits photonic spin-orbit coupling to create an asymmetric optical transfer function for real-time phase imaging. We demonstrate experimentally the effect of the asymmetry with the generation of high contrast pseudo-3D intensity images of phase variations in an optical wavefield without the need for post-processing. This non-interferometric method has potential applications in biological live cell imaging and real-time wavefront sensing.
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ItemOptical Janus Effect in Large Area Multilayer Plasmonic Films(Wiley, 2022)Plasmonic and other nanoparticles have attracted considerable interest for their role in structural coloration. The optical “Janus” effect, where the color of light reflected from a partially transmitting film depends on whether the device is viewed from the substrate or the coating side, is observed using a variety of nanostructured films. Herein, the optical Janus effect produced by homogeneous thin-film structures comprising only four layers of three different materials with a total thickness less than 300 nm is demonstrated. An asymmetric Fabry–Perot (FP) nanocavity is formed with a dielectric film bounded by two different metal films of nanoscale thickness. The semitransparent device has a transmitted color that is independent of the viewing direction. A broad color palette is available through the selection of various thicknesses and film materials. In addition to the directional optical effect, the device possesses iridescence properties and can generate images by selective removal of regions of one of the metallic films using simple photolithography. From a manufacturing perspective, this device is scalable and holds significant promise for applications in architecture, producing decorative features, and the development of overt and covert security features.
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ItemOn-chip optical image processing with plasmonic metasurfaces(IEEE, 2020)We propose the utilization of plasmonic resonant wave-guide gratings for ultracompact image processing in transmission. We experimentally demonstrate two-dimensional edge-detection in amplitude images and contrast enhancement of images of biological samples.
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ItemOptical Metasurfaces for Processing of Amplitude and Phase Images(Optica Publishing Group, 2021)We investigate the utilization of plasmonic resonant waveguide gratings for all-optical image processing in transmission. We experimentally demonstrate edge-detection in amplitude- as well as phase images and contrast enhancement of images of biological samples.
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ItemMeta-optical and thin film devices for all-optical information processing(American Institute of Physics, 2021-09-01)All-optical spatial frequency filtering has a long history with many applications now commonly replaced with digital alternatives. Although optical approaches are attractive in that they minimize energy requirements and images can be manipulated in real time, they are relatively bulky compared to the compact electronic devices that are now ubiquitous. With emerging interest in nanophotonic approaches to all-optical information processing, these approaches to enhancing images and performing phase visualization are attracting significant interest. Metasurfaces have been demonstrated as tailored alternatives to conventional spatial filters, but utilizing the spatial frequency sensitivity of these and thin film devices also has the potential to form the basis for ultracompact approaches to image processing. There are, however, significant challenges remaining to realize this promise. This review summarizes the current status of research in this rapidly growing field, places it in the context of the history of all-optical spatial filtering, and assesses prospects for future directions.
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ItemNanophotonics enhanced coverslip for phase imaging in biology(SPRINGERNATURE, 2021-05-08)The ability to visualise transparent objects such as live cells is central to understanding biological processes. Here we experimentally demonstrate a novel nanostructured coverslip that converts phase information to high-contrast intensity images. This compact device enables real-time, all-optical generation of pseudo three-dimensional images of phase objects on transmission. We show that by placing unstained human cancer cells on the device, the internal structure within the cells can be clearly seen. Our research demonstrates the significant potential of nanophotonic devices for integration into compact imaging and medical diagnostic devices. The nanophotonics enhanced coverslip (NEC) enables ultra-compact phase imaging of samples placed directly on top of the device. Visualisation of artificial phase objects and unstained biological cells is demonstrated.
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ItemPlasmonic Metasurfaces for Optical Information Processing(SPIE-INT SOC OPTICAL ENGINEERING, 2019-01-01)Optical spatial frequency filtering is a key method for information processing in biological and technical imaging. While conventional approaches rely on bulky components to access and filter the Fourier plane content of a wavefield, nanophotonic approaches for spatial frequency filtering have recently gained attention. Here computational and experimental progress towards the design and demonstration of metasurfaces with spatial frequency filtering capability for optical image processing will be presented. Using the example of a metasurface consisting of radial rod trimers we demonstrate its potential to perform edge enhancement in an amplitude image and conversion of phase gradients in a wavefield into intensity modulations. The presented results indicate a potential avenue for ultra-compact image processing devices with applications in biological live-cell imaging.
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ItemUltracompact Camera Pixel with Integrated Plasmonic Color Filters(WILEY-V C H VERLAG GMBH, 2019-09-17)Photodetector size imposes a fundamental limit on the amount of information that can be recorded by an image sensor. Compact, high-resolution sensors are generally preferred for portable electronic devices such as mobile phones and digital cameras, and as a result, a significant effort has been invested in improving the image quality provided by small-area image sensors. Reducing photodetector size, however, still faces challenges in implementation requiring improvements in current technology to meet the demand for ultracompact imaging systems such as cameras. An issue with a decrease in size is associated with photodetectors utilizing color filters. In most commonly used camera designs these filters are made of dyes or pigments and incompatible with the complementary metal-oxide-semiconductor fabrication process. They are, therefore, fabricated in two different technological processes and require subsequent alignment. As the pixel size decreases, the alignment of these layers becomes challenging. Furthermore, dye-based filters need to have a thickness of the order of micrometers to ensure sufficient absorption. Here a compact, low-cost color sensor is proposed and experimentally demonstrated utilizing monolithically integrated plasmonic antennas that have a nanoscale thickness and are fabricated in the same technological process with photodetector matrix.