271 research outputs found
Giant nonlinear response at the nanoscale driven by bound states in the continuum
Being motivated by the recent prediction of high- supercavity modes in
subwavelength dielectric resonators, we study the second-harmonic generation
from isolated subwavelength AlGaAs nanoantennas pumped by a structured light.
We reveal that nonlinear effects at the nanoscale can be enhanced dramatically
provided the resonator parameters are tuned to the regime of the bound state in
the continuum. We predict a record-high conversion efficiency for nanoscale
resonators that exceeds by two orders of magnitude the conversion efficiency
observed at the conditions of magnetic dipole Mie resonance, thus opening the
way for highly-efficient nonlinear metadevices.Comment: 7 pages, 4 figures, 1 tabl
Photonique intégrée nonlinéaire sur plate-formes CMOS compatibles pour applications du proche au moyen infrarouge
Integrated photonics offers a vast choice of nonlinear optical phenomena that could potentially be used for realizing chip-based and cost-effective all-optical signal processing devices that can handle, in principle, optical data signals at very high bit rates. The new components and technological solutions arising from this approach could have a considerable impact for telecom and datacom applications. Nonlinear optical effects (such as the optical Kerr effect or the Raman effect) can be potentially used for realizing active devices (e.g. optical amplifiers, modulators, lasers, signal regenerators and wavelength converters). During the last decade, the silicon on insulator (SOI) platform has known a significant development by exploiting the strong optical confinement, offered by this material platform, which is key for the miniaturization and realization of integrated optical devices (such as passive filters, splitters, junctions and multiplexers). However, the presence of strong nonlinear losses in the standard telecom band (around 1.55 ”m) prevents some applications where a strong nonlinear optical response is needed and has motivated the research of more suitable material platforms. The primary goal of this thesis was the study of material alternatives to crystalline silicon (for instance hydrogenated amorphous silicon) with very low nonlinear losses and compatible with the CMOS process in order to realize integrated photonics devices based on nonlinear optical phenomena. Alternatively, the use of longer wavelengths (in the mid-IR) relaxes the constraints on the choice of the material platform, through taking advantage of lower nonlinear losses, for instance on the SiGe platform, which is also explored in this thesis. This work is organized as follows. In the first chapter we provide an overview of the nonlinear optical effects used to realize all optical signal processing functions, focusing on the key parameters that are essential (optical confinement and dispersion engineering) for integrated optical components, and presenting the main models used in this thesis. This chapter also includes a review of the main demonstrations reported on crystalline silicon, to give some benchmarks. Chapter 2 introduces the use of photonic crystals as integrated optical structures that can significantly enhance nonlinear optical phenomena. First we present photonic crystal cavities, with a demonstration of second and third harmonic generation that makes use of an original design. In the second part of the chapter, we describe the main features and challenges associated with photonic crystal waveguides in the slow light regime, which will be used later in chapter 4. In chapter 3, we report the experimental results related to the characterization of the optical nonlinear response of integrated waveguides made of two materials that are alternative to crystalline silicon : the hydrogenated amorphous silicon, probed in the near infrared, and the silicon germanium, probed in the mid-infrared. The model presented in chapter 1 is extensively used here for extracting the nonlinear parameters of these materials and it is also extended to account for higher order nonlinearities in the case of silicon germanium tested at longer wavelengths. This chapter also includes a comparison of the nonlinear properties of these two material platforms with respect to the standard SOI. In chapter 4, we combine the use of a material platform that is better suited than SOI for nonlinear applications with integrated photonics structures that are more advanced that those used in chapter 3. Here we describe the design of (slow) modes in photonic crystal waveguides made in hydrogenated amorphous silicon fully embedded in silica. [...]La photonique intĂ©grĂ©e offre la possibilitĂ© dâexploiter un vaste bouquet de phĂ©nomĂšnes optique nonlinĂ©aires pour la gĂ©nĂ©ration et le traitement de signaux optiques sur des puces trĂšs compactes et Ă des dĂ©bits potentiels extrĂȘmement rapides. De nouvelles solutions et technologies de composants pourraient ĂȘtre ainsi rĂ©alisĂ©es, avec un impact considĂ©rable pour les applications tĂ©lĂ©com et datacom. Lâutilisation de phĂ©nomĂšnes optiques nonlinĂ©aires (e.g. effet Kerr optique, effet Raman) permet mĂȘme dâenvisager la rĂ©alisation de composants actifs (e.g. amplificateurs, modulateurs, lasers, rĂ©gĂ©nĂ©rateurs de signaux et convertisseurs en longueur dâonde).Pendant cette derniĂšre dĂ©cennie, les efforts ont principalement portĂ© sur la plateforme Silicium sur isolant (SOI), profitant du fort confinement optique dans ce matĂ©riau, qui permet la miniaturisation et intĂ©gration de composants optiques clĂ©s (e.g. filtres passifs, jonctions coupleurs et multiplexeurs). Cependant, la prĂ©sence de fortes pertes nonlinĂ©aires dans ce matĂ©riau aux longueurs dâonde dâintĂ©rĂȘt (i.e. autour de 1.55 ”m dans les tĂ©lĂ©communications) limite certaines applications pour lesquelles une forte rĂ©ponse nonlinĂ©aire est nĂ©cessaire et motive la recherche de nouvelles plates-formes, mieux adaptĂ©es. Lâobjectif premier de cette thĂšse Ă©tait ainsi lâĂ©tude de matĂ©riaux alternatifs au Si cristallin, par exemple le silicium amorphe hydrogĂ©nĂ©, alliant de trĂšs faibles pertes nonlinĂ©aires et une compatibilitĂ© CMOS, pour la rĂ©alisation de dispositifs photoniques intĂ©grĂ©s qui exploitent les phĂ©nomĂšnes nonlinĂ©aires. Alternativement, lâutilisation de longueurs dâonde plus Ă©levĂ©es (dans le moyen-IR) permet de relaxer la contrainte sur le choix de la filiĂšre matĂ©riau, en bĂ©nĂ©ficiant de pertes nonlinĂ©aires rĂ©duites, par exemple dans la filiĂšre SiGe, Ă©galement explorĂ©e dans cette thĂšse. Ce travail est organisĂ© de la façon suivante. Le premier chapitre donne un iii panorama des phĂ©nomĂšnes nonlinĂ©aires qui permettent de rĂ©aliser du traitement tout-optique de lâinformation, en mettant en Ă©vidence les paramĂštres clĂ©s Ă maitriser (confinement optique, ingĂ©nierie de dispersion) pour les composants dâoptique intĂ©grĂ©e, et en prĂ©sentant le cadre de modĂ©lisation de ces phĂ©nomĂšnes utilisĂ© dans le travail de thĂšse. Il inclut Ă©galement une revue des dĂ©monstrations marquantes publiĂ©es sur Silicium cristallin, donnant ainsi des points de rĂ©fĂ©rence pour la suite du travail. Le chapitre 2 introduit les cristaux photoniques comme structures dâoptique intĂ©grĂ©e permettant dâexalter les phĂ©nomĂšnes nonlinĂ©aires. On sâintĂ©resse ici aux cavitĂ©s, avec une dĂ©monstration de gĂ©nĂ©ration de deuxiĂšme et troisiĂšme harmoniques qui exploite un design original. Ce chapitre dĂ©crit Ă©galement les enjeux associĂ©s Ă lâutilisation de guides Ă cristaux photoniques en rĂ©gime de lumiĂšre lente, qui serviront de fondements pour le chapitre 4. Le chapitre 3 prĂ©sente les rĂ©sultats de caractĂ©risation de la rĂ©ponse nonlinĂ©aire associĂ©e Ă des guides rĂ©alisĂ©s dans deux matĂ©riaux alternatifs au silicium cristallin : le silicium amorphe hydrogĂ©nĂ© testĂ© dans le proche infrarouge et le silicium germanium testĂ© dans le moyen infrarouge. Le modĂšle prĂ©sentĂ© au chapitre 1 est exploitĂ© pour dĂ©duire la rĂ©ponse de ces deux matĂ©riaux, et il est mĂȘme Ă©tendu pour rendre compte dâeffets nonlinĂ©aires dâordre plus Ă©levĂ© dans le cas du silicium germanium Ă haute longueur dâonde. Ce chapitre inclut Ă©galement une discussion sur la comparaison des propriĂ©tĂ©s nonlinĂ©aires de ces deux matĂ©riaux avec le SOI standard. Le chapitre 4 combine lâutilisation dâune plate-forme plus prometteuse que le SOI, avec des structures photoniques plus avancĂ©es que les simples guides rĂ©fractifs utilisĂ©s au chapitre 3 : il dĂ©crit lâingĂ©nierie de modes (lents) dans des guides Ă cristaux photoniques en silicium amorphe hydrogĂ©nĂ© et enterrĂ©s dans la silice. [...
Biostimulant Effects of Seed-Applied Sedaxane Fungicide: Morphological and Physiological Changes in Maize Seedlings
Most crops are routinely protected against seed-born and soil-borne fungal pathogens through seed-applied fungicides. The recently released succinate dehydrogenase inhibitor (SDHI), sedaxane\uae, is a broad-spectrum fungicide, used particularly to control Rhizoctonia spp., but also has documented growth-enhancement effects on wheat. This study investigates the potential biostimulant effects of sedaxane and related physiological changes in disease-free maize seedlings (3-leaf stage) at increasing application doses (25, 75 and 150 \u3bcg a.i. seed-1) under controlled sterilized conditions. We show sedaxane to have significant auxin-like and gibberellin-like effects, which effect marked morphological and physiological changes according to an approximate saturation dose-response model. Maximum benefits were attained at the intermediate dose, which significantly increased root length (+60%), area (+45%) and forks (+51%), and reduced root diameter as compared to untreated controls. Sedaxane enhanced leaf and root glutamine synthetase (GS) activity resulting in greater protein accumulation, particularly in the above-ground compartment, while glutamate synthase (GOGAT) activity remained almost unchanged. Sedaxane also improved leaf phenylalanine ammonia-lyase (PAL) activity, which may be responsible for the increase in shoot antioxidant activity (phenolic acids), mainly represented by p-coumaric and caffeic acids. We conclude that, in addition to its protective effect, sedaxane can facilitate root establishment and intensify nitrogen and phenylpropanoid metabolism in young maize plants, and may be beneficial in overcoming biotic and abiotic stresses in early growth stages
Biostimulant Effects of Seed-Applied Sedaxane Fungicide: Morphological and Physiological Changes in Maize Seedlings
Most crops are routinely protected against seed-born and soil-borne fungal pathogens through seed-applied fungicides. The recently released succinate dehydrogenase inhibitor (SDHI), sedaxaneÂź, is a broad-spectrum fungicide, used particularly to control Rhizoctonia spp., but also has documented growth-enhancement effects on wheat. This study investigates the potential biostimulant effects of sedaxane and related physiological changes in disease-free maize seedlings (3-leaf stage) at increasing application doses (25, 75 and 150 ÎŒg a.i. seed-1) under controlled sterilized conditions. We show sedaxane to have significant auxin-like and gibberellin-like effects, which effect marked morphological and physiological changes according to an approximate saturation dose-response model. Maximum benefits were attained at the intermediate dose, which significantly increased root length (+60%), area (+45%) and forks (+51%), and reduced root diameter as compared to untreated controls. Sedaxane enhanced leaf and root glutamine synthetase (GS) activity resulting in greater protein accumulation, particularly in the above-ground compartment, while glutamate synthase (GOGAT) activity remained almost unchanged. Sedaxane also improved leaf phenylalanine ammonia-lyase (PAL) activity, which may be responsible for the increase in shoot antioxidant activity (phenolic acids), mainly represented by p-coumaric and caffeic acids. We conclude that, in addition to its protective effect, sedaxane can facilitate root establishment and intensify nitrogen and phenylpropanoid metabolism in young maize plants, and may be beneficial in overcoming biotic and abiotic stresses in early growth stages
High-index-contrast grating reflector with beam steering ability for the transmitted beam
High-index contrast grating mirrors providing wave front control of the transmitted light as well as high reflectivity over a broad bandwidth are suggested and both numerically and experimentally investigated. General design rules to engineer these structures for different applications are derived. Such grating mirrors would have a significant impact on low cost laser fabrication, since a more efficient integration of optoelectronic modules can be achieved by avoiding expensive external lens systems
Shaping the Radiation Pattern of Second-Harmonic Generation from AlGaAs Dielectric Nanoantennas
We fabricate AlGaAs nanodisk antennas on a glass substrate and demonstrate experimentally the shaping of radiation patterns and polarization of the second harmonic emission in both forward and backward directions.The paper and the participation of all the authors have been
made possible in the framework of the Erasmus Mundus
NANOPHI project, contract number 2013 5659/002-001. L.C.,
C.D.A., and A.L. acknowledge financial support from U.S. Army
(âEngineering second order nonlinear effects in optical
antennasâ) and CARIPLO (âSHAPES, Second-HArmonic
Plasmon-Enhanced Sensingâ). D.N. acknowledges the support
of the Australian Research Council and of the Visiting Program
of the University of Brescia
Enhanced second-harmonic generation from magnetic resonance in AlGaAs nanoantennas
We designed AlGaAs-on-aluminium-oxide all-dielectric nanoantennas with magnetic dipole resonance at near-infrared wavelengths
Near to short wave infrared light generation through AlGaAs-on-insulator nanoantennas
AlGaAs-on-insulator (AlGaAs-OI) has recently emerged as a novel promising platform for nonlinear optics at the nanoscale. Among the most remarkable outcomes, second harmonic generation (SHG) in the visible/near infrared spectral region has been demonstrated in AlGaAs-OI nanoantennas (NA). In order to extend the nonlinear frequency generation towards the short wave infrared window, in this work we propose and demonstrate via numerical simulations difference frequency generation (DFG) in AlGaAs-OI NAs. The NA geometry is finely adjusted in order to obtain simultaneous optical resonances at the pump, signal and idler wavelengths, which results in an efficient DFG with conversion efficiencies up to 0.01%. Our investigation includes the study of the robustness against random variations of the NA geometry that may occur at fabrication stage. Overall, these outcomes identify a new potential and yet unexplored application of AlGaAs-OI NAs as compact devices for the generation and control of the radiation pattern in the near to short infrared spectral region
Evidence for cascaded third harmonic generation in non-centrosymmetric gold nanoantennas
The optimization of nonlinear optical processes at the nanoscale is a crucial
step for the development of nanoscale photon sources for quantum-optical
networks. The development of innovative plasmonic nanoantenna designs and
hybrid nanostructures to enhance optical nonlinearities in very small volumes
represents one of the most promising routes. In such systems, the upconversion
of photons can be achieved with high efficiencies via third-order processes,
such as third harmonic generation (THG), thanks to the resonantly-enhanced
volume currents. Conversely, second-order processes, such as second harmonic
generation (SHG), are often inhibited by the symmetry of metal lattices and of
common nanoantenna geometries. SHG and THG processes in plasmonic
nanostructures are generally treated independently, since they both represent a
small perturbation in the light-matter interaction mechanisms. In this work, we
demonstrate that this paradigm does not hold in general, by providing evidence
of a cascaded process in THG, which is fueled by SHG and sizably contributes to
the overall yield. We address this mechanism by unveiling an anomalous
fingerprint in the polarization state of the nonlinear emission from
non-centrosymmetric gold nanoantennas and point out that such cascaded
processes may also appear for structures that exhibit only moderate SHG yields
- signifying its general relevance in plasmon-enhanced nonlinear optics. The
presence of this peculiar mechanism in THG from plasmonic nanoantennas at
telecommunication wavelengths allows gaining further insight on the physics of
plasmon-enhanced nonlinear optical processes. This could be crucial in the
realization of nanoscale elements for photon conversion and manipulation
operating at room-temperature.Comment: 25 pages, 4 figure
- âŠ