Control of light absorbance using plasmonic grating based perfect absorber at visible and near-infrared wavelengths

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Metasurfaces Based on Phase-Change Material as a Reconfigurable Platform for Multifunctional Devices

Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices.1115sciescopu

The role of current loop in harmonic generation from magnetic metamaterials in two polarizations

In this paper, we investigate the role of the current loop in the generation of second and third harmonic signals from magnetic metamaterials. We will show that the fact that the current loop in the magnetic resonance acts as a source for nonlinear effects and it consists of two orthogonal parts, leads to the generation of two harmonic signals in two orthogonal polarizations

Dual-Functional Nanoscale Devices Using Phase-Change Materials: A Reconfigurable Perfect Absorber with Nonvolatile Resistance-Change Memory Characteristics

Integration of metamaterial and nonvolatile memory devices with tunable characteristics is an enthusing area of research. Designing a unique nanoscale prototype to achieve a metasurface with reliable resistive switching properties is an elusive goal. We demonstrate a method to exploit the advantages of a phase-change material (PCM) as a metamaterial light absorber and a nanoscale data storage device. We designed and simulated a metamaterial perfect absorber (MPA) that can be reconfigured by adjusting the visible light properties of a chalcogenide-based PCM. The suggested perfect absorber is based on a Ge2Sb2Te5 (GST) film, and is tuned between two distinct states by heat treatment. Furthermore, we fabricated and characterized a resistive switching memory (ReRAM) device with the same features. The MPA/ReRAM device with a conventional metal/dielectric/metal structure (Ag/GST/Al2O3/Pt) consisted of arrays of Ag squares patterned on a GST thin film and an alumina-coated Pt mirror on a glass substrate. Based on the numerical data, amorphous GST showed perfect absorbance in the visible spectrum, whereas, crystalline GST showed broadband perfect absorbance. The fabricated ReRAM device exhibited uniform, bidirectional, and programmable memory characteristics with a high ON/OFF ratio for nonvolatile memory applications. The elucidated origin of the bipolar resistive switching behavior is assigned to the formation and rupture of conductive filaments.11Nsciescopu

Optimization of colour generation from dielectric nanostructures using reinforcement learning

Recently, a novel machine learning model has emerged in the field of reinforcement learning known as deep Q-learning. This model is capable of finding the best possible solution in systems consisting of millions of choices, without ever experiencing it before, and has been used to beat the best human minds at complex games such as, Go and chess, which both have a huge number of possible decisions and outcomes for each move. With a human-level intelligence, it has solved the problems that no other machine learning model has done before. Here, we show the steps needed for implementing this model to an optical problem. We investigate the colour generation by dielectric nanostructures and show that this model can find geometrical properties that can generate much purer red, green and blue colours compared to previously reported results. The model found these results in 9000 steps from a possible 34.5 million solutions. This technique can easily be extended to predict and optimise the design parameters for other optical structures. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement11Ysciescopu