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This is the final version of the article. Available from Wiley via the DOI in this record. ; All data need to evaluate the conclusions in this Communication are present in this Communication and/or the Supporting Information. Additional data related to this Communication may be requested from the corresponding author (H.B.; harish.bhaskaran@materials.ox.ac.uk or Oxford Research Archive for Data (https://ora.ox.ac.uk). ; Inspired by the great success of fiber optics in ultrafast data transmission, photonic computing is being extensively studied as an alternative to replace or hybridize electronic computers, which are reaching speed and bandwidth limitations. Mimicking and implementing basic computing elements on photonic devices is a first and essential step toward all-optical computers. Here, an optical pulse-width modulation (PWM) switching of phase-change materials on an integrated waveguide is developed, which allows practical implementation of photonic memories and logic devices. It is established that PWM with low peak power is very effective for recrystallization of phase-change materials, in terms of both energy efficiency and process control. Using this understanding, multilevel photonic memories with complete random accessibility are then implemented. Finally, programmable optical logic devices are demonstrated conceptually and experimentally, with logic "OR" and "NAND" achieved on just a single integrated photonic phase-change cell. This study provides a practical and elegant technique to optically program photonic phase-change devices for computing applications. ; This research was supported via the Engineering and Physical Sciences Research Council Manufacturing Fellowships (EP/J018694/1), the Wearable and Flexible Technologies (WAFT) collaboration (EP/M015173/1), the Chalcogenide Advanced Manufacturing Partnership (EP/M015130/1), and the European Union's Horizon 2020 research and innovation program (780848, Fun‐COMP project).

High-pressure optical absorption and Raman scattering measurements have been performed in defect chalcopyrite (DC) CdGa2Se4 up to 22 GPa during two pressure cycles to investigate the pressure-induced order-disorder phase transitions taking place in this ordered-vacancy compound. Our measurements reveal that on decreasing pressure from 22 GPa, the sample does not revert to the initial phase but likely to a disordered zinc blende (DZ) structure the direct bandgap and Raman-active modes of which have been measured during a second upstroke. Our measurements have been complemented with electronic structure and lattice dynamical ab initio calculations. Lattice dynamical calculations have helped us to discuss and assign the symmetries of the Raman modes of the DC phase. Additionally, our electronic band structure calculations have helped us in discussing the order-disorder effects taking place above 6¿8 GPa during the first upstroke. © 2012 American Institute of Physics ; This study was supported by the Spanish government MICINN under Grant No. MAT2010-21270-C04-01/03/04; by the Generalitat Valenciana (Project No. GV06/151), by MALTA Consolider Ingenio 2010 project (CSD2007-00045), by the Vicerrectorado de Investigacion y Desarrollo of the Universitat Politecnica de Valencia (UPV2012-1469), and by the Spanish MICINN under Project No. CTQ2009-14596-C02-01 and Comunidad de Madrid and the European Social Fund Grant No. S2009/PPQ-1551 4161893 (QUI-MAPRES). E.P-G., J.L-S., A. M., and P.R-H. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster. ; Gomis Hilario, O.; Vilaplana Cerda, RI.; Manjón Herrera, FJ.; Pérez-González, E.; López-Solano, J.; Rodríguez-Hernández, P.; Muñoz, A. (2012). High-pressure optical and vibrational properties of CdGa2Se4: Order-disorder processes in adamantine compounds. Journal of Applied Physics. 111(1):135181-1351815. https://doi.org/10.1063/1.3675162 ; S ; 135181 ; 1351815 ; 111 ; 1 ; A. MacKinnon, in Tables of Numerical Data and Functional ...

As contamination and environmental degradation increase nowadays, there is a huge demand for new eco-friendly materials. Despite its use for thousands of years, cellulose and its derivatives have gained renewed interest as favourable alternatives to conventional plastics, due to their abundance and lower environmental impact. We report the fabrication of photonic and plasmonic structures by moulding hydroxypropyl cellulose into sub-micrometric periodic lattices, using soft lithography. This is an alternative way to achieve structural colour in this material which is usually obtained exploiting its chiral nematic phase. Cellulose based photonic crystals are biocompatible and can be dissolved in water or not depending on the derivative employed. Patterned cellulose membranes exhibit tuneable colours and may be used to boost the photoluminescence of a host organic dye. Furthermore, we show how metal coating these cellulose photonic architectures leads to plasmonic crystals with excellent optical properties acting as disposable surface enhanced Raman spectroscopy substrates. ; The authors would like to acknowledge M. Simón and A. Gómez for AFM measurements. The Spanish Ministerio de Economía, Industria y Competitividad (MINECO) is gratefully acknowledged for its support through Grant No. SEV-2015-0496 in the framework of the Spanish Severo Ochoa Centre of Excellence program and also for its support through Grant MAT2016-79053-P. AM was funded by a Ramón y Cajal fellowship (RYC-2014-16444). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 637116, ENLIGHTMENT). ; Peer reviewed

Cephalopods are known as the chameleons of the sea due to their remarkable camouflage abilities. They can rapidly and accurately tune their skin's coloration, pattern, and texture to blend into the surrounding environment. This dynamic camouflage capability stems from their transparent dermis/epidermis and the optically-active, protein-based nanostructures found in embedded skin cells known as leucophores, chromatophores, and iridophores. Respectively, these cells provide a high contrast reflective white background, mechanically actuated pigmented pixels, and chemically actuated Bragg reflectors that function in concert to modulate incident visible light. Considerable effort has been devoted to understanding and emulating cephalopod camouflage abilities in the visible region of the electromagnetic spectrum, but few studies have attempted to translate these principles to the infrared region for nighttime stealth applications. Thus, the fabrication of bio-inspired infrared-reflective devices for infrared camouflage remains an unexplored area of research. To address this challenge, we have developed a high-throughput strategy for the gram-scale production, purification, and self-assembly of a unique cephalopod structural protein, reflectin. We eliminate time-consuming and costly steps commonly used in protein expression and purification and instead replace them with rapid, sequential filtrations all while retaining high purity (>99%). Using this reflectin protein, we fabricate dynamically tunable biomimetic camouflage coatings with relevance to industrial and military applications. We demonstrate reversible control of reflectin film coloration shifts over a range of 1,200 nm from the visible into the near infrared using an acid vapor stimulus. We then coat reflectin on flexible, transparent substrates that can adhere to arbitrary surfaces, and modulate the film reflectance by mechanical strain or applied heat. Finally, we prove electrical actuation can also induce reversible color change in our films based on the applied bias. Together, our findings represent a key step towards the development of wearable biomimetic color and shapeshifting technologies that utilize diverse means of actuation. Future biophysical and materials studies lending insight into the tunability of reflectin-based Bragg reflector structures and textured reflectin surfaces could provide additional methods to enhance overall film brightness, angle-dependence, and color modulation for advanced camouflage applications.

[EN] We propose a new programmable integrated photonic device, the Field Programmable Photonic Array, which follows a similar rationale as that of Field Programmable Gate Arrays and Field Programmable Analog Arrays in electronics. This high-level concept, basic photonic building blocks, design principles, and technology and physical implementation are discussed. Experimental evidence of its feasibility is also provided. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement ; European Research Council (ERC ADG-2016 UMWP-Chip 741415); Generalitat Valenciana (PROMETEO 2017/017 research excellency award); European Union COST Action (CA16220 EUIMWP); Spanish MINECO (Ramon y Cajal fellowship RYC-2014-16247 for I. Gasulla). ; © 2018 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited ; Pérez-López, D.; Gasulla Mestre, I.; Capmany Francoy, J. (2018). Field-programmable photonic arrays. Optics Express. 26(21):27265-27278. https://doi.org/10.1364/OE.26.027265 ; S ; 27265 ; 27278 ; 26 ; 21

Certain bird species have evolved spectacular colors that arise from organized nanostructures of melanin. Its high refractive index (similar to 1.8) and broadband absorptive properties enable vivid structural colors that are nonsusceptible to photo-bleaching. Mimicking natural melanin structural coloration could enable several important applications, in particular, for non-iridescent systems with colors that are independent of incidence angle. Here, we address this by forming melanin photonic crystal microdomes by inkjet printing. Owing to their curved nature, the microdomes exhibit noniridescent vivid structural coloration, tunable throughout the visible range via the size of the nanoparticles. Large-area arrays (>1 cm(2)) of high-quality photonic microdomes could be printed on both rigid and flexible substrates. Combined with scalable fabrication and the nontoxicity of melanin, the presented photonic microdomes with noniridescent structural coloration may find use in a variety of applications, including sensing, displays, and anticounterfeit holograms. ; Funding Agencies|Wenner-Gren Foundation; Swedish Research CouncilSwedish Research Council; Knut and Alice Wallenberg foundationKnut & Alice Wallenberg Foundation; Swedish Foundation for Strategic researchSwedish Foundation for Strategic Research; Linkoping University; Wallenberg Wood Science Center the Wallenberg Wood Science Centre; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

This article belongs to the Special Issue Sol-Gel Chemistry Applied to Materials Science. ; Transparent glass-ceramics have shown interesting optical properties for several photonic applications. In particular, compositions based on oxide glass matrices with fluoride crystals embedded inside, known as oxyfluoride glass-ceramics, have gained increasing interest in the last few decades. Melt-quenching is still the most used method to prepare these materials but sol-gel has been indicated as a suitable alternative. Many papers have been published since the end of the 1990s, when these materials were prepared by sol-gel for the first time, thus a review of the achievements obtained so far is necessary. In the first part of this paper, a review of transparent sol-gel glass-ceramics is made focusing mainly on oxyfluoride compositions. Many interesting optical results have been obtained but very little innovation of synthesis and processing is found with respect to pioneering papers published 20 years ago. In the second part we describe the improvements in synthesis and processing obtained by the authors during the last five years. The main achievements are the preparation of oxyfluoride glass-ceramics with a much higher fluoride crystal fraction, at least double that reported up to now, and the first synthesis of NaGdF₄ glass-ceramics. Moreover, a new SiO₂ precursor was introduced in the synthesis, allowing for a reduction in the treatment temperature and favoring hydroxyl group removal. Interesting optical properties demonstrated the incorporation of dopant ions in the fluoride crystals, thus obtaining crystal-like spectra along with higher efficiencies with respect to xerogels, and hence demonstrating that these materials are a suitable alternative for photonic applications. ; This work was supported by MINECO under projects MAT2013-48246-C2-1-P, MAT2013-48246-C2-2-P, and MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE) and Basque Country Government IT-943-16 and PPG17/07. The authors are grateful for access to the Spanish Beamline (SpLine) at the ESRF facilities in Grenoble to perform experiments MA-3350 and 25-01-1014. Jose Joaquín Velázquez also acknowledges MINECO for Grant FPDI-2013-16895. ; Peer reviewed

Light localization and intensity enhancement in a woodpile layer-by-layer photonic crystal, whose interlayer distance along the light propagation direction is gradually varied, has been theoretically predicted and experimentally demonstrated. The phenomenon is shown to be related to the progressive slowing down and stopping of the incident wave, as a result of the gradual variation of the local dispersion. The light localization is chromatically resolved, since every frequency component is stopped and reflected back at different positions along the crystal. It has been further discussed that the peculiar relation between the stopping position and the wave vector distribution can substantially increase the enhancement factor to more than two orders of magnitude. Compared to previously reported one-and two-dimensional photonic crystal configurations, the proposed scheme has the advantage of reducing the propagation losses by providing a three-dimensional photonic bandgap confinement in all directions. The slowing down and localization of waves inside photonic media can be exploited in optics and generally in wave dynamics, in many applications that require enhanced interaction of light and matter. ; Authors acknowledge financial support of NATO SPS research grant No: 985048. K.S. acknowledges financial support of Spanish Ministerio de Ciencia e Innovacion and European Union FEDER through project FIS2015-65998- C2-1-P. H.K. also acknowledges partial support of the Turkish Academy of Science.