Scientific Publications of the University of Toulouse II Le Mirail
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Self-written high-efficiency single-mode optical link using a single near-infrared photopolymerization step
No full textAccepté pour publication dans J. Lightwave Tech.International audienceWe present a method for fabricating a self-written waveguide (SWW) between two optical fibers that are single-mode (SM) at 850 nm (780HP/ core diameter: 4.4 µm). The basic principle consists in exposing an acrylic photopolymer formulation sensitive in the near-infrared range (NIR) to a laser beam transmitted simultaneously from both fibers placed face to face, to build a continuous, flexible and self-aligned optical link. The specificity of the presented process (NIR-SM-SWW) lies in the use of a writing wavelength identical to that intended for singlemode propagation in the fibers. This enables the creation in a single step of a SWW directly adapted to the fundamental mode to be transmitted. A precise pre-positioning stage is used to optimize the process. For best photochemical conditions, a coupling efficiency as high as 82 % (-0.86 dB loss) is demonstrated for a 300 µm-long link. The effect of fiber-to-fiber axial and lateral distances is also investigated to estimate the propagation loss and misalignment tolerance, respectively. In addition, measurements performed by quantitative phase optical microscopy indicate a homogeneous index profile in the guide. Using these data, optical modeling is performed and compared to experiments, confirming that a high efficiency SM link is actually fabricated, without the need for further fabrication of an external cladding. This method could therefore be easily applied to the SM connection of a SM VCSEL (vertical-cavity surface-emitting laser) to a SM fiber, which is of major interest for the development of compact optical communications and instrumentation systems
Directional light scattering in Mie-resonant Si particles with ultra-thin Au shells
No full textInternational audienceMetamaterial research has sought to create nanostructures with strong directional optical scattering to control light propagation at the nanoscale. Core–shell architectures comprised of both resonant cores and resonant shells are suggested as candidate particles in which the spectral overlap of the electric and magnetic dipoles is controlled to create strong directional scattering. In this study, Au-decorated Si core–shell (Si@Au) particles are presented, studying the role of the architecture (particulate, discontinuous shells vs continuous) and dimensions of the shell. The core–shell particles are synthesized by first creating Si particles, through the thermal disproportionation of hydrogen silsesquioxane (HSQ), which are then decorated with ≈4 nm diameter Au nanoparticles. The resonant behavior of the core–shell particles is characterized using electron energy-loss spectroscopy mapping and optical single-particle scatter spectroscopy. These observations are supported by T-matrix simulations and Mie-theory calculations of the scattering spectra, which show that, compared to Si, Si@Au particles demonstrate a dampened magnetic dipole resonance for smaller Si core diameters (100–130 nm) and an enhanced magnetic dipole resonance for larger Si core sizes (150–200 nm). The study indicates that the previously reported hybridized modes do not exist in particulate Au shells around a Si core and can only exist in continuous plasmonic shells. Thus, it is shown here how important it is to be as precise as possible regarding the nanomaterial architecture used in simulations. No configuration of Si@Au core–shell particles with a particulate shell could be found that strongly enhanced directional scattering, and a continuous shell may do so only modestly. However, the simulations show that the synthesis of thin, continuous Ag shells might represent an alternative route towards achieving good directional scattering properties.</p
Front-surface cooling of infrared thermophotovoltaic cells
No full textInternational audienceThis paper proposes a front-surface cooling method for thermophotovoltaic (TPV) cells utilizing microfluidic channels for efficient heat dissipation. Unlike conventional back-surface cooling, front-surface cooling minimizes thermal resistance by directly cooling the top surface of the cell. The microfluidic channel layer also functions as an antireflection layer through the gradual change in the refractive index. The proposed cooling method was evaluated using a thermo-fluid analysis, considering factors such as the emitter temperature, cell reflectance, thermal resistance, and fluid optical properties. We examined liquids with ideal absorption characteristics and actual liquids whose absorption coefficients were measured. The results showed that front-surface cooling significantly outperformed back-surface cooling in terms of the net power density. This method is particularly advantageous for high emitter temperatures or in cases where the thermal resistance between the cell and backsurface liquid is high. Moreover, this study highlights the potential application of the cooling method in bifacial TPV cells, which can generate electricity from thermal radiation incident on both sides. Bifacial cells offer higher power generation per unit area but face cooling challenges. The proposed cooling technique addresses these challenges, paving the way for innovative TPV system configurations and improved performance
The Phoenicians’ Impiety in the Narrative Process of Herodotus’ Work: The Theft of the Statue of Apollo as an Omen of Barbaric Defeat
No full textInternational audienceHerodotus regularly uses narrative processes in order to explain peace and war. In this framework, religious elements play an important role, especially in the course of the Persian Wars. The plain of Marathon in 490 BCE is one example of this that clearly explains the Persian defeat. The author uses an ethical composition: the defeat is symbolically the fault of the Phoenicians from the Persian fleet who stole a statue of Apollo on the island of Delos, but the Persians, who disturb the balance between men and gods with their act of pride, are also guilty. Herodotus chooses the Phoenicians as narrative mediators of the Persians’ downfall, because they are always present at cultural, moral or physical borders. From the Greeks’ point of view, the Phoenicians stealing the statue of Apollo is an omen of the barbaric defeat in the course of the First Persian War
Les savants du linéaire B, les machines à écrire et le Babel des caractères
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Runtime Monitoring for Safety-Critical Vision-based Runway Detection
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Styliser le populaire ? Politique du style et des voix dans "Le Chiendent" de Raymond Queneau
No full textInternational audienceEn 1933, Raymond Queneau publie "Le Chiendent", son premier roman, à la fois farceur et métaphysique, qui affirme la volonté de styliser la langue parlée sans revendiquer cette démarche comme politique. Presque cent ans plus tard, dans un moment où les hiérarchies linguistiques et les formes d’exclusion symbolique sont de nouveau interrogées, ce geste littéraire mérite d’être relu. Dans l’esprit des thèses "Sur le concept d’histoire" de Walter Benjamin, il ne s’agit pas ici de revenir à un texte fondateur pour en célébrer l’audace, mais de le relire à partir d’un présent traversé par d’autres urgences. Benjamin rappelle que certains fragments du passé ne deviennent lisibles qu’au moment où un danger les éclaire autrement. "Le Chiendent", souvent lu comme une fantaisie de langage, se donne aussi comme un lieu d’ambivalences : entre expérimentation formelle et esthétisation du populaire, entre fascination pour l’oralité et effacement des voix. Que nous dit aujourd’hui ce style sur les tensions de l’époque de Queneau ? Et qu’est-ce qu’il donne à penser sur les nôtres, en creux, en écho, ou par contraste ? L’analyse portera sur plusieurs influences qui nourrissent l’écriture du roman : la lecture de Voyage au bout de la nuit, les débats contemporains sur la langue grecque (qui, en réalité, cristallisent aussi des enjeux politiques), les expériences linguistiques de Queneau durant son service militaire, ou encore l’imaginaire des revues enfantines, comme "Les Pieds Nickelés". Ces matériaux hétérogènes se croisent dans un projet stylistique singulier, qui se construit à distance des postures militantes. Queneau affirme en effet une position paradoxale : puiser dans le langage populaire, non pour affirmer un rapport au peuple ou une lutte, mais parce qu’il n’existe, selon lui, « rien de réellement sacré dans notre français contemporain ». Il écrit : « Je ne vois aucune raison pour ne pas élever le langage populaire à la dignité de langage écrit, et source d’une nouvelle littérature, d’une nouvelle poésie. » Cette esthétisation du commun, sans revendication du commun, produit un décalage dont il devient possible, aujourd’hui, de mesurer les effets
Du conte marmontélien (La Bergère des Alpes) au livret et à l’opéra. Le son dans tous ses états
No full textInternational audienceLe conte moral marmontélien La Bergère des Alpes, paru en 1761, est fondé sur la voix chantée et le hautbois. Cet article étudie par conséquent le traitement du sonore dans le conte, mais mène aussi une étude comparative avec le livret de la pastorale, rédigé par Marmontel, et observe la partition élaborée par le compositeur Joseph Kohaut en 1766
Le legs des savoirs européens sur l'Afrique dans quelques dictionnaires et encyclopédies (d'histoire et de géographie ancienne, moderne, physique) du 'long' XVIIIe siècle
No full textInternational audienceL’article propose d’explorer les entrées « Afrique » de plusieurs dictionnaires et encyclopédies du xviiie siècle, du Grand dictionnaire historique de Moréri à l’Encyclopédie méthodique. Quel est le savoir et quel est le discours sur ce savoir transmis par les dictionnaires au long cours? Ceux-ci puisent bien souvent leurs informations dans la littérature viatique, qui réitère des préjugés au sujet des Africains; néanmoins, on peut penser à un renouvellement des savoirs sur l’Afrique
Extended-Precision FMA under Parameterized Double-Word Overlap: Tight Error Bounds and Examples
No full textWe study fast fused multiply--add (FMA) kernels for approximating in extended precision using double-word (DW) representations in floating-point (FP) arithmetic. We focus on how worst-case guarantees depend on the overlap between the high and low parts, modeled by parameterized conditions of the form (and two- and three-parameter variants for multiple DW inputs). We consider the dominance regime and its DW analogues (e.g., and ), which occur in fast paths for elementary-function evaluation and in cancellation-free constructions. Within this regime, we tighten and extend error analyses for several FMA-based schemes used in recent extended-precision implementations. We analyze FP/DW and DW/DW variants, derive explicit worst-case constants for both the returned low part and the overall relative error, and provide matching worst-case examples. The resulting bounds give a unified and quantitative view of how DW-overlap assumptions affect the accuracy of fast extended-precision FMA building blocks