Backward phase-matched second-harmonic generation from stacked metasurfaces

We demonstrate phase-matched second-harmonic generation (SHG) from three-dimensional metamaterials consisting of stacked metasurfaces. To achieve phase matching, we utilize a novel mechanism based on phase engineering of the metasurfaces at the interacting wavelengths, facilitating phase-matched SHG in the unconventional backward direction. By stacking up to five metasurfaces, we obtain the expected factor of 25 enhancement in SHG efficiency. Our results motivate further investigations to achieve higher conversion efficiencies also with more complex wavefronts.Comment: 5 pages, 3 figures, supplementary materia

Optimization and uncertainty quantification of gradient index metasurfaces

The design of intrinsically flat two-dimensional optical components, i.e., metasurfaces, generally requires an extensive parameter search to target the appropriate scattering properties of their constituting building blocks. Such design methodologies neglect important near-field interaction effects, playing an essential role in limiting the device performance. Optimization of transmission, phase-addressing and broadband performances of metasurfaces require new numerical tools. Additionally, uncertainties and systematic fabrication errors should be analysed. These estimations, of critical importance in the case of large production of metaoptics components, are useful to further project their deployment in industrial applications. Here, we report on a computational methodology to optimize metasurface designs. We complement this computational methodology by quantifying the impact of fabrication uncertainties on the experimentally characterized components. This analysis provides general perspectives on the overall metaoptics performances, giving an idea of the expected average behavior of a large number of devices

Effects of eight neuropsychiatric copy number variants on human brain structure

Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen’s d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions

Nanostructures pour l'exaltation d'effets non linéaires

Infrared sources based on second order effects are interesting tools for atmospheric pollutants spectrometry thanks to their wide tunability. Such effects nevertheless demand strong incident powers or massive non linear crystals to be efficient. A new way to reduce their size consists in realizing frequency conversion with the help of plasmonic nanostructures containing dielectric inclusions showing a non zero second order susceptibility. Light is greatly harvested and concentrated at resonance leading to the creation of a great quantity of non linear polarization, so as to further enhance non linear optics effects.This work begins with a study of nanoresonators through developing a simulation tool for one dimensional nanostructured multilayered structures. Three architectures are retained : slit nanoresonators, optical Helmholtz nanoresonators and waveguides based on guided mode resonances. In every case, the conception focuses on the finding of bi- and even of tri-resonant geometries to achieve mode matching for second harmonic of difference frequency generation.Clean room fabrication is then detailed step by step following the important works that have permitted the fabrication of samples showing a very good quality.Les sources infrarouges basées sur des effets d'optique du second ordre constituent de très bons outils de spectrométrie des polluants présents dans l'atmosphère, grâce notamment à leur grande accordabilité spectrale. Ils demandent toutefois une forte puissance lumineuse incidente et une grande quantité de matériau non linéaire pour être efficaces. On peut les rendre très compactes en réalisant la conversion de fréquence à l'aide de nanostructures plasmoniques contenant des inclusions diélectriques présentant une susceptibilité du deuxième ordre non nulle. La lumière y est très fortement concentrée à la résonance augmentant fortement la quantité de polarisation non linéaire produite, afin d'y exalter les effets d'optique non linéaire.Ce travail s'attaque d'abord à la conception de nano-résonateurs grâce au développement d'un outil de simulation d’empilements nanostructurés selon une dimension. Trois architectures sont étudiées : les nanorésonateurs de type sillon, les nanorésonateurs de Helmholtz et les guides d'ondes à résonances de modes guidés. Dans chaque cas, le dimensionnement passe par la détermination de géométries bi- voire tri-résonantes pour la réalisation d'accord de modes en génération de second harmonique ou de différence de fréquences.La fabrication en salle blanche des résonateurs sillons et guides d'ondes est ensuite exposée, suite à un important travail de développement technologique, qui a permis l’obtention d’échantillons de très bonne qualité

Nanostructures for nonlinear effects enhancement

Les sources infrarouges basées sur des effets d'optique du second ordre constituent de très bons outils de spectrométrie des polluants présents dans l'atmosphère, grâce notamment à leur grande accordabilité spectrale. Ils demandent toutefois une forte puissance lumineuse incidente et une grande quantité de matériau non linéaire pour être efficaces. On peut les rendre très compactes en réalisant la conversion de fréquence à l'aide de nanostructures plasmoniques contenant des inclusions diélectriques présentant une susceptibilité du deuxième ordre non nulle. La lumière y est très fortement concentrée à la résonance augmentant fortement la quantité de polarisation non linéaire produite, afin d'y exalter les effets d'optique non linéaire.Ce travail s'attaque d'abord à la conception de nano-résonateurs grâce au développement d'un outil de simulation d’empilements nanostructurés selon une dimension. Trois architectures sont étudiées : les nanorésonateurs de type sillon, les nanorésonateurs de Helmholtz et les guides d'ondes à résonances de modes guidés. Dans chaque cas, le dimensionnement passe par la détermination de géométries bi- voire tri-résonantes pour la réalisation d'accord de modes en génération de second harmonique ou de différence de fréquences.La fabrication en salle blanche des résonateurs sillons et guides d'ondes est ensuite exposée, suite à un important travail de développement technologique, qui a permis l’obtention d’échantillons de très bonne qualité.Infrared sources based on second order effects are interesting tools for atmospheric pollutants spectrometry thanks to their wide tunability. Such effects nevertheless demand strong incident powers or massive non linear crystals to be efficient. A new way to reduce their size consists in realizing frequency conversion with the help of plasmonic nanostructures containing dielectric inclusions showing a non zero second order susceptibility. Light is greatly harvested and concentrated at resonance leading to the creation of a great quantity of non linear polarization, so as to further enhance non linear optics effects.This work begins with a study of nanoresonators through developing a simulation tool for one dimensional nanostructured multilayered structures. Three architectures are retained : slit nanoresonators, optical Helmholtz nanoresonators and waveguides based on guided mode resonances. In every case, the conception focuses on the finding of bi- and even of tri-resonant geometries to achieve mode matching for second harmonic of difference frequency generation.Clean room fabrication is then detailed step by step following the important works that have permitted the fabrication of samples showing a very good quality

Visible imaging system optical design by continuous optimization of glasses

Choice of lenses materials in optical design is crucial to reduce aberrations down to an acceptable level. Commercial glasses do not cover a continuous range of refractive indices and must be selected in a discrete library making them discrete variables in any optimization design process to achieve the final optical design to be manufactured. This paper proposes an alternative method to avoid the complicated discrete variables optimization process thanks to a two-steps continuous optimization methodology starting with fictitious glasses models before jumping to the real glasses optimization design. The illustration of this process and achieved results are presented on an example of optical system which validates our proposed method

Advancing wavefront shaping with resonant metasurface

International audienceIn metasurface design, the use of look-up tables based on a local periodicity approximation have been tradi-tionally employed, but can result in sub-optimal designs due to lack of consideration of near-field couplingeffects, which are particularly important for resonant systems. This paper explores the benefits of taking intoaccount near-field coupling while optimizing non-local resonant metasurfaces to enhance their performance forwavefront shaping, including the state-of-the-art Huygens’s metasurface

Advancing wavefront shaping with resonant nonlocal metasurfaces: beyond the limitations of lookup tables

International audienceResonant metasurfaces are of paramount importance in addressing the growing demand for reduced thickness and complexity, while ensuring high optical efficiency. This becomes particularly crucial in overcoming fabrication challenges associated with high aspect ratio structures, thereby enabling seamless integration of metasurfaces with electronic components at an advanced level. However, traditional design approaches relying on lookup tables and local field approximations often fail to achieve optimal performance, especially for nonlocal resonant metasurfaces. In this study, we investigate the use of statistical learning optimization techniques for nonlocal resonant metasurfaces, with a specific emphasis on the role of near-field coupling in wavefront shaping beyond single unit cell simulations. Our study achieves significant advancements in the design of resonant metasurfaces. For transmission-based metasurfaces, a beam steering design outperforms the classical design by achieving an impressive efficiency of 80% compared to the previous 23%. Additionally, our optimized extended depth-of-focus (EDOF) metalens yields a remarkable five-fold increase in focal depth, a four-fold enhancement in focusing power compared to conventional designs and an optical resolution superior to 600 cycle/mm across the focus region. Moreover, our study demonstrates remarkable performance with a wavelength-selected beam steering metagrating in reflection, achieving exceptional efficiency surpassing 85%. This far outperforms classical gradient phase distribution approaches, emphasizing the immense potential for groundbreaking applications in the field of resonant metasurfaces