HAL Portal IOGS (nstitut d'Optique Graduate School)
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Experimental demonstration of Continuous-Variable Quantum Key Distribution with a silicon photonics integrated receiver
No full text11 pages, 13 figures; Changed figure 8, acknowledgments updatedInternational audienceQuantum Key Distribution (QKD) is a prominent application in the field of quantum cryptography providing information-theoretic security for secret key exchange. The implementation of QKD systems on photonic integrated circuits (PICs) can reduce the size and cost of such systems and facilitate their deployment in practical infrastructures. To this end, continuous-variable (CV) QKD systems are particularly well-suited as they do not require single-photon detectors, whose integration is presently challenging. Here we present a CV-QKD receiver based on a silicon PIC capable of performing balanced detection. We characterize its performance in a laboratory QKD setup using a frequency multiplexed pilot scheme with specifically designed data processing allowing for high modulation and secret key rates. The obtained excess noise values are compatible with asymptotic secret key rates of 2.4 Mbit/s and 220 kbit/s at an emulated distance of 10 km and 23 km, respectively. These results demonstrate the potential of this technology towards fully integrated devices suitable for high-speed, metropolitan-distance secure communication
Dynamics of Cu-Zr metallic glass devitrification under ultrafast laser excitation revealed by atomistic modeling
No full textInternational audienceThe physics of metallic glass local devitrification employing ultrafast laser irradiation is the cradle of complex phenomena that are still not understood despite its applicative potential in material processing for nanotechnology. This paper reports a theoretical simulation combining the two temperature model and classical molecular dynamics simulations to unravel the mechanisms that lead to the localized phase transition in Cu-Zr metallic glass. According to observations, the initial composition of amorphous samples plays an essential role, in addition to nonequilibrium thermodynamic processes caused by the laser energy deposition that alters the atomic environment. We further demonstrate that specific compositions devitrify despite its high glass-forming ability. The thermodynamic conditions fostering the emergence of a stable nanocrystalline phase are clearly established. The compressive pressure wave and the rapid heating process caused by ultrafast laser energy deposition synergistically contribute to disrupt the microstructure of the glass significantly, thereby initiating the devitrification process. Results are discussed using additional classical MD simulations that provide valuable insights for interpreting the distinct contributions of temperature and pressure to the phase transformation. Finally, the impact of the formed nanocrystals on the phononic thermal conductivity of the alloy is presented confirming the potential application of the laser-induced devitrification process for the development of a new generation of nanoarchitectured materials. I
Tribological behavior of DLC film models in base oils: Analysis of influence of sp3/sp2 ratio and hydrogen content
No full textInternational audienceDLC coatings have been proven in formulated oils used in the automotive industry. The development of electric cars and its consequences on the future of the internal combustion engine makes it increasingly necessary that these coatings take their place in other applications where lubrication is generally of lower quality such as for example strips cold rolling where DLC shows significant potential both for production and finishing cold rolling. As a result, the interest of the behavior of these coatings in base oils takes on a new dimension. In this study, we explore the influence of the composition and the sp 3 /sp 2 ratio on tribological behavior of DLC coatings in mineral and synthetic base oils. Hydrogenated DLC films deposited by conventional PECVD with various levels of hydrogen measured by Elastic Recoil Detection Analysis (ERDA) and non-hydrogenated DLC films deposited by PLD in the nanosecond mode (ns-PLD) and by cathodic arc evaporation, thus allowing to have different sp 3 /sp 2 ratios confirmed by Multiwavelength Raman spectrometry, are tested and compared. The tests are performed on a ball-on-flat device with coated balls to better evaluate wear level. The behavior of highly hydrogenated DLC is of particular interest; with a very high level of durability in both base oils and friction level which comparatively varies between low and very low depending on the base oil
Leveraging PAC-Bayes Theory and Gibbs Distributions for Generalization Bounds with Complexity Measures
No full textAISTATS 2024International audienceIn statistical learning theory, a generalization bound usually involves a complexity measure imposed by the considered theoretical framework. This limits the scope of such bounds, as other forms of capacity measures or regularizations are used in algorithms. In this paper, we leverage the framework of disintegrated PAC-Bayes bounds to derive a general generalization bound instantiable with arbitrary complexity measures. One trick to prove such a result involves considering a commonly used family of distributions: the Gibbs distributions. Our bound stands in probability jointly over the hypothesis and the learning sample, which allows the complexity to be adapted to the generalization gap as it can be customized to fit both the hypothesis class and the task
Influence of Hydrogen on the Radiation-Induced Attenuation of Ge-doped Optical Fibers
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Polarization-Dependent Anisotropy of LIPSSs’ Morphology Evolution on a Single-Crystal Silicon Surface
No full textInternational audienceUtilizing the principle of laser-induced periodic surface structures (LIPSSs), this research delves into the morphological evolution of single-crystal silicon surfaces irradiated by a near-infrared picosecond laser through a scanning mode. With the increase in laser energy density, the nanostructure morphology on single-crystal silicon surfaces induced by incident lasers with different polarization directions sequentially produces high spatial-frequency LIPSSs (HSFLs) with a period of 220 nm ± 10 nm parallel to the laser polarization, low spatial-frequency LIPSSs (LSFLs) with a period of 770 nm ± 85 nm perpendicular to the direction of the polarization, and groove structures. Furthermore, by varying the angle between the laser polarization and the scanning direction, the study examined the combined anisotropic effects of the laser polarization scanning direction angle and the laser polarization crystal orientation angle on the genesis of LIPSSs on single-crystal silicon (100) surfaces. The experiments revealed polarization-related anisotropic characteristics in the morphology of HSFLs. It was found that when the polarization angle approached 45°, the regularity of the LSFLs deteriorated, the modification width decreased, and the periodicity increased. This is critical for the precise control of the LSFLs’ morphology
A Study on Hierarchical Text Classification as a Seq2seq Task
No full textInternational audienceWith the progress of generative neural models, Hierarchical Text Classification (HTC) can be cast as a generative task. In this case, given an input text, the model generates the sequence of predicted class labels taken from a label tree of arbitrary width and depth. Treating HTC as a generative task introduces multiple modeling choices. These choices vary from choosing the order for visiting the class tree and therefore defining the order of generating tokens, choosing either to constrain the decoding to labels that respect the previous level predictions, up to choosing the pre-trained Language Model itself. Each HTC model therefore differs from the others from an architectural standpoint, but also from the modeling choices that were made. Prior contributions lack transparent modeling choices and open implementations, hindering the assessment of whether model performance stems from architectural or modeling decisions. For these reasons, we propose with this paper an analysis of the impact of different modeling choices along with common model errors and successes for this task. This analysis is based on an open framework coming along this paper that can facilitate the development of future contributions in the field by providing datasets, metrics, error analysis toolkit and the capability to readily test various modeling choices for one given model
Regeneration of Phosphosilicate Optical Fiber Dosimeters operating in the Visible Domain
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Progrès dans les solutions de surveillance des rayonnements et d'analyse des données du CERN pour les applications de rayonnement vers l'électronique
No full textThis thesis focuses on the aspects related to the protection of electronics in the CERN radiation environment, also known as Radiation Hardness Assurance. In particular, the two core pillars are investigated, namely i) characterization of the CERN's radiation environment through the currently available radiation monitors, ii) applications of commercial silicon solid-state detectors for monitoring radiation fields and particle beams (relevant for electronics testing). In the first thesis branch, the focus is on the two largest CERN accelerators, the Super Proton Synchrotron (SPS) and the Large Hadron Collider (LHC). Thanks to multiple complementary radiation monitors, such as Beam Loss Monitors, Optical Fibers, and RadMons, and developed data analysis software solutions, the comprehensive view of the radiation spatial distribution and its time evolution. In the case of the SPS, the focus is on the 2021 operation and related beam loss mechanisms. For LHC, the accelerator restart in 2022 is covered. The second branch covers a silicon solid-state detector calibration and applications. Within the calibration, the detector response in proton-, neutron-, and heavy-ion beams is demonstrated. Furthermore, it is shown how the detector can be used for complete beam monitoring, in terms of flux, energy, and spatial distribution. The silicon detector-related work is concluded with the applications for radiation field characterization, such as atmospheric or accelerator one. The work covers also engineering aspects that enabled the synthesis of the related huge datasets.Cette thèse se concentre sur les aspects liés à la protection de l'électronique dans l'environnement radiatif du CERN, également connu sous le nom assurance durcissement aux radiations. En particulier, les deux piliers principaux sont étudiés, à savoir i) la caractérisation de l'environnement radiatif du CERN à travers les moniteurs de radiations actuellement disponibles, ii) les applications des détecteurs à semi-conducteurs en silicium commerciaux pour la surveillance des champs de radiation et des faisceaux de particules (pertinents pour les tests électroniques).Dans la première branche de la thèse, l'accent est mis sur les deux plus grands accélérateurs du CERN, le SPS et le LHC. Grâce à plusieurs moniteurs de radiations complémentaires, tels que les moniteurs de perte de faisceau, les fibers optiques et les RadMons, ainsi que des solutions logicielles d'analyse de données développées, une vue d'ensemble de la distribution spatiale du radiations et de son évolution temporelle est obtenue. Dans le cas du SPS, l'accent est mis sur le fonctionnement de 2021 et les mécanismes de perte de faisceau associés. Pour le LHC, le redémarrage de l'accélérateur en 2022 est couvert
Design of a freeform, wide field of view, high angular resolution four-mirrors system working in the visible and near-infrared spectrum
No full textInternational audienceSituational awareness requires systems with a wide field of view and a high angular resolution. Tackling both requirements is easier using freeform optics and a curved sensor and allows for compact systems. In this paper, we present an imaging system that fulfills these requirements in the visible spectrum, and the steps in the optimization process that lead to a viable system in terms of stray light