74 research outputs found
Reconfigurable phase-change optical metasurfaces: novel design concepts to practicable devices
Optical metasurfaces have been proven to be capable of controlling amplitude, phase and polarization of optical beams without the need of bulky geometries, making them really attractive for the development of compact photonic devices. Recently, their combination with chalcogenide phase-change materials (traditionally employed in non-volatile optical and electrical memories), whose refractive index can be reversibly and repeatedly controlled, has been proposed to yield low power consumption tunable metasurfaces having several functionalities in a single device. However, despite phase-change memories are commercially available since various decades now, the unification of phase-change materials with metasurfaces towards real life applications is becoming a formidable task, mainly due to the several engineering branches involved in this technology, which sometimes compromise each other in a non-trivial way. This includes thermo/optical, thermo/electric, and chemical incompatibilities which are typically not taken into account by researchers working in the field, resulting in devices having exciting reconfigurable properties, but at the same time, lack of practicability. This thesis is therefore dedicated to the development of novel phase-change metasurface architectures which could partially or totally address such engineering problems. Particular emphasis has been put in the realization of reconfigurable metasurfaces for active wavefront control, as such a functionality remains relatively unexplored. The first part of this thesis focuses in the first experimental demonstration of active, reconfigurable non-mechanical beam steering devices working the near-infrared. This was achieved via integration of ultra-thin films of chalcogenide phase-change materials (in this case, the widely employed alloy Ge2Sb2Te5) within the body of a dielectric spacer in a plasmonic metal/insulator/metal metasurface architecture. Active, and optically reversible beam steering between two different angles with efficiencies up to 40% were demonstrated. The second part of this work shows the work carried out in metal-free metasurfaces as a way to manipulate optical beams with high efficiency in both transmission and/or reflection. This was achieved via combination of all-dielectric silicon nanocylinders with deeply-subwavelenght sized Ge2Sb2Te5 inclusions. By strategic placement of the phase-change inclusions in the regions of high electric field density, independent and active control of the metasuface resonances is demonstrated, with modulations depths as high as 70% and 65% in reflection and transmission respectively. Multilevel, and fully reversible optically-induced switching of the phasechange layer is also reported, with up to 11 levels of tunability over 8 switching cycles. Finally, the last section of this thesis introduces the concept of hybrid dielectric/plasmonic phase-change metasurfaces having key functional benefits when compared to both purely dielectric and plasmonic approaches. The proposed architectures showed great versatility in terms of both active amplitude and phase control, offering the possibility of designing devices for different purposes (i.e. such as active absorbers/modulators or beam steerers with enhanced efficiency) employing the same unit-cell configuration with minor geometry re-optimizations. Initial device experimental demonstrations of such an approach are discussed, as well as their potential in terms of delivering in-situ electrical switching capabilities using a metallic ground plane as a resistive heater.Engineering and Physical Sciences Research Council (EPSRC
Phase-change metasurfaces for dyamic beam steering and beam shaping in the infrared
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordWe present novel phase-change material based
metasurfaces for dynamic, recnofigurable and efficient wavefront
shaping in the infrared spectrum. Dynamic control and
reconfigurability was obtained by incorporating an ultra-thin layer
of the widely-used phase change material Ge2Sb2Te5. Our approach
exploits hybrid dielectic/plasmonic resonances to achieve local
(subwavelength) phase control of light with low losses. A full 2Ï€
optical phase coverage was achieved with this approach, which
allows for a wide flexibility in terms of realizable designs. To
illustrate this concept, dynamic beam steering devices and
reconfigurable planar focusing mirrors (both operating at optical
telecommunications wavelengths) and their performance
investigated. Absolute efficiencies up to 65% are achieved,
significantly higher than the efficiencies of more commonly reported
plasmonic-based phase-change metasurfaces.CDW acknowledges funding via the US Naval Research
Laboratories ONRG programme (#N62909-16-1-2174) and the
EPSRC ChAMP and WAFT grants (EP/M015130/1 and
EP/M015173/1). CRdeG acknowledges funding via the EPSRC
CDT in Metamaterials (EP/L015331/1). CRdeG Acknowledges
Joaquin Faneca-Ruedas and Dr Anna Baldycheva
Infrared Phase-Change Meta-Devices with In-Situ Switching
This is the author accepted manuscript. The final version is available from the European Phase Change and Ovonics Symposium via the link in this recordWe describe a possible device design approach and an experimental test platform suitable for the
realization and characterization of phase-change based meta-devices incorporating in-situ
switching and operating at infrared wavelengths. Measurements on such a prototype device
working at 1.55 µm are presented.US Naval Research LaboratoriesEngineering and Physical Sciences Research Council (EPSRC
All-dielectric hybrid silicon/Ge2Sb2Te5 optical metasurfaces for tunable and switchable light control in the near infrared
This is the final version.We report a novel reconfigurable metasurface based on the combination of all-dielectric arrays of
silicon meta-atoms, with deeply subwavelength (< λ0/150) Ge2Sb2Te5 layers. Our approach allows to selectively
and individually control electric and magnetic resonances.Engineering and Physical Sciences Research Council (EPSRC
Overcoming diffusion issues in hybrid phase-change metasurfaces
This is the final version.The optical performance of phase-change metasurfaces can be irreversibly degraded by the effect of thermally activated diffusion during device switching. Here we present a systematic case-study of this effect in metasurfaces designed for modulation in the O and C telecommunication bands and a method for addressing such issues using ultra-thin Si3N4 barrier layers.Engineering and Physical Sciences Research Council (EPSRC
Lens numerical aperture control with phase-change metasurfaces
This is the author accepted manuscript.The control of lens numerical aperture has many applications, including photography, imaging, and laser processing. Here we introduce active control of numerical aperture via a focusing phase-change meta-mirror. This can potentially operate at high speed in a low cost, light and compact format. We demonstrate designs for both infrared (3000 nm) and visible (632.8 nm) wavelengths.Engineering and Physical Sciences Research Council (EPSRC)Atomic Weapons Establishment (AWE
Optical and Thermal Design and Analysis of Phase-Change Metalenses for Active Numerical Aperture Control
This is the final version. Available on open access from MDPI via the DOI in this recordThe control of a lens's numerical aperture has potential applications in areas such as photography and imaging, displays, sensing, laser processing and even laser-implosion fusion. In such fields, the ability to control lens properties dynamically is of much interest, and active meta-lenses of various kinds are under investigation due to their modulation speed and compactness. However, as of yet, meta-lenses that explicitly offer dynamic control of a lens's numerical aperture have received little attention. Here, we design and simulate active meta-lenses (specifically, focusing meta-mirrors) using chalcogenide phase-change materials to provide such control. We show that, operating at a wavelength of 3000 nm, our devices can change the numerical aperture by up to a factor of 1.85 and operate at optical intensities of the order of 1.2 × 109 Wm-2. Furthermore, we show the scalability of our design towards shorter wavelengths (visible spectrum), where we demonstrate a change in NA by a factor of 1.92.Engineering and Physical Sciences Research Council (EPSRC)Margarita Salas fellowshi
Remote Thermal Sources for Switching Phase-Change Material-Based Metasurfaces
This is the final version.Atomic Weapons Establishment (AWE) plcEngineering and Physical Sciences Research Council (EPSRC
Switching of Phase-Change Optical Metasurfaces via Remote Thermal Sources
This is the final version.Atomic Weapons Establishment (AWE) plcEngineering and Physical Sciences Research Council (EPSRC
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