Microcellules photoniques pour les horloges atomiques et étalons de fréquences.

Sujets de thèse

Intitulé de la thèse
Microcellules photoniques pour les horloges atomiques et étalons de fréquences.
Publication du sujet sur le site de l’ABG : OUI
Nature du financement : Financement institutionnel, Contrat Doctoral, Financement régional, Contrats université sur projets,)
Domaine de compétences principal (pour l’ABG) : Physique
Domaine de compétences secondaire (pour l’ABG) : Sciences pour l’Ingénieur
Spécialité de doctorat : Electronique des hautes fréquences, Photonique et Systèmes

Lieu de travail
Institut de recherche XLIM
Université de Limoges
Laboratoire d’accueil : XLIM/PHOTONIQUE

Le sujet de thèse proposé repose sur le développement de fibre à cristal photonique remplie de vapeur atomique pour les applications d’étalons de fréquence micro-ondes.

Présentation de l’équipe de recherche
The Gas-Phase Photonic and Microwave Materials (GPPMM) is a newly established research group of XLIM Research institute. It stems from Prof. Benabid GPPM (Gas-Phase Photonic Materials) research group at the University of Bath which is now transferred with all the laboratory equipments to XLIM on one hand, and from the pre-existing experience and facilities of XLIM in optical fiber on the other hand. The GPPM has been the world pioneering and leading research group on hollow-core PCF and its applications for gas-phase materials based quantum and nonlinear optics. This international leadership is substantiated by a recent report by the Institute of Physics (IOP) and the Engineering and Physical Sciences Research Council (EPSRC, UK) on the research of optics and photonics in the United Kingdom, which has ranked Prof. Benabid’s GPPM as a word-leading research group (see footnote1 for the internet link). A further example of this pioneering and leading role was demonstrated during the leading conference in laser and optoelectronic CLEO 2008, Baltimore, US, where the GPPM group contribution to the “symposium on hollow-core photonic crystal fiber” represented 45% of the 20 presented papers. In parallel, XLIM work on photonic crystal fiber has enjoyed an international standing.

Résumé de la thèse en français
Le projet s’inscrit dans un des programmes scientifiques du GPPMM dont le but est de développer une horloge atomique ultra-compacte. Celle-ci consiste en un système auto-suffisant qui repose sur une approche originale utilisant la technologie de la microcellule photonique et celle des MEMS. La microcellule photonique sera composée d’une fibre creuse à cristal photonique remplie de rubidium ou césium hermétiquement attachée à un système fibré et couplé à un oscillateur local miniature à base de MEMS. Le but du projet est de lever un des verrous technologiques majeurs qui est de confiner des alcalins en phase vapeur dans un cœur creux de très faible section (quelques dizaines de micromètres) sans engendrer une désexcitation des ces dites atomes. La solution envisagée pour annihiler la relaxation des atomes lors des chocs sur la paroi du cœur de la fibre est de recouvrir cette dernière avec un revêtement anti-relaxant. Par conséquent, le projet consistera à élaborer des matériaux en collaboration avec le SPCTS (laboratoire Science des Procédés Céramiques et de Traitements de Surface), à en déposer des couches minces à l’intérieur du cœur creux d’une fibre à cristal photonique, et enfin à monter un dispositif expérimental de spectroscopie optique pour la caractérisation anti-relaxante de la couche déposée. Le candidat bénéficiera de l’association des compétences uniques du GPPMM/XLIM dans la conception et la fabrication de fibres optiques creuses à cristal photonique, et du SPCTS dans l’élaboration de matériaux.

Résumé de la thèse en anglais
The project is part of one the scientific programs of the GPPMM, and whose goal is to develop an ultra-compact atomic clock. This consists of a self-sufficient device based on an original approach that amalgamates the fibre photonics technology with that of MEMS. The device is a photonic microcell (PMC) that is coupled to MEMS based local oscillator. The PMC consists of a hollow photonic crystal fiber (HC-PCF) filled with alkali atoms such as rubidium or cesium.
The project goal is to lift one of the major technological hurdles which consists of successfully confining alkali atomic vapors in a micrometer-scale hollow core without causing a dephasing to the optically excited atoms. The proposed solution is to drastically reduce the relaxation of atoms during their impacts on the inner wall of the fibre core by coating it with an anti-relaxation layer. The project will consist thus in synthesising materials in collaboration with the SPCTS, and depositing thin layers of the synthesised material inside the core of a HC-PCF, and finally setting-up an optical spectroscopy experiment for characterizing the anti–relaxing features of the deposited coating. The candidate will benefit from the combination of the unique expertise of GPPMM / XLIM in the design and fabrication of HC-PCF, and of the SPCTS in synthesising novel materials.

Description complète du sujet de thèse
In a most remarkable demonstration of human endeavour, clock performance has improved over 100 million times during the last century, culminating in the development of the laser-cooled atomic beam clock with a long-term precision of better than 1 in 1015; i.e. a timekeeping ability of not losing nor gaining 1 milli-second every 3 millennia. Although the performance of these atomic clocks is unquestioned and is properly celebrated, their size and complexity, and hence their accessibility, is still an issue. The atomic beam and fountain clocks used for primary standards are run as large facilities, requiring a high degree of maintenance and man-power. On the other hand, the ubiquitous use of clocks in virtually every human activity calls for high performance to be delivered in a small and compact package. Furthermore, the functionalities of atomic clocks extend beyond their timekeeping capabilities as their quantum resonances and coherences are at the heart of ultra-stable laser sources, high precision magnetometers, gravimeters or gyroscopes, and they play a fundamental role in quantum information. Indeed, in today’s world, the craving for these high performance functionalities to be delivered in miniature and portable devices is as pervasive as it is pressing.
The project is part of the aim to develop a fully integrated photonic approach to develop what would be the first all-optical fibre microwave atomic clocks, which combine compactness and integrability and a performance approaching that of the facility-based atomic beam or fountain clocks. This will rely on the GPPMM expertise in hollow-core photonic crystal fibre (HC-PCF) and their gas-filled integrated form called photonic microcells (PMC). The PMC confines gases or atomic vapours together with light over mode areas of order μm2, keeping them in interaction over length scales a million times longer than the Rayleigh range. The result of this encounter is the best of two worlds: an unprecedented efficiency and a friendly compactness, as illustrated by groundbreaking results in extremely low-light level nonlinear optics, laser induced guidance, quantum optics and laser frequency metrology. However, the exceptional potential of the PMCs can thus be realised only if the dephasing due to the micro-confinement induced enhanced collisions with the walls of the hollow-core fibre. This limitation can be circumvented by a variety of means. These include one or a combination of the following: (i) enlarging the fibre-core, (ii) applying an anti-relaxation coating to the core; or (iii) introducing a buffer gas.
The doctoral project aims is to identify, synthesise and deposit a material in the inner wall of the HC-PCF that exhibits the best anti-relaxation properties. To this end, the candidate will synthesise several materials (e.g. polymer sol-gel and aero-gel based materials) in collaboration with SPCTS. Furthermore, the candidate will capitalise on GPPM expertise in coating the fibre-core to further control the layer deposition in order to optimise the dephasing and the LIAD effect. This task is of paramount importance as the potential degree of anti-relaxation in HC-PCF coated with paraffin or PDMS is yet to be determined. Even though the principle of an anti-relaxation coating has been known since the sixties, the cumulated data so far is empirical and fragmented. The degree of “anti-relaxation” of a particular coating remains terra incognita as it depends on (i) the geometry of the container, (ii) the chosen coating material and (iii) the deposition process. Consequently, with the aim of finding the best trade-off between the degree of anti-relaxation, thermal properties and the ease of deposition, we will explore a range of different coating materials. This will include a number of organosilanes but also sol-gels and aerogels, materials. Finally, the candidate will characterise the impact of the coating and the confined geometry on the spectral lines and coherences using ultra-high precision means such as NICE-OHMS spectroscopy.
The results of this project will be a defining milestone in the development of stable and compact fibre-based atomic clocks, but also the advent of highly efficient all-fibre devices for applications in, for example, high resolution spectroscopy, metrology, quantum information and quantum sensors.

Objectifs scientifiques de la thèse
Le travail demandé comprendra une étude bibliographique sur l’état de l’art les horloges atomiques, l’élaboration de matériaux anti-relaxant puis leur déposition en couches minces à l’intérieur du cœur creux d’une fibre à cristal photonique. Enfin la dernière étape consistera à monter un dispositif expérimental de spectroscopie optique pour la caractérisation anti-relaxante de la couche déposée.

Compétences à l’issue de la thèse
Les compétences attendues à l’issue de la thèse seront:
– Connaissance forte dans le domaine «temps-fréquence», horloge atomique
– Expertise concernant la conception et la fabrication de fibres optiques et de certains matériaux anti-relaxant
– Forte expérience dans la caractérisation des procédés linéaires et nonlinéaires dans les fibres optiques
– Forte expérience dans la diffusion de la culture scientifique (communications internationales, articles, séminaires, …)
– Forte autonomie

Mots clés (séparés par des virgules)
Temps-fréquence, horloge atomique, fibre optique, photonique des structures à bandes interdites, interaction gaz/lumière, effets non-linéaires.
Conditions restrictive de candidature (nationalité, âge, …) : NON

Expérience/profil souhaité(e)
Double profil: matériaux et photonique

Modalité de dépôt des candidatures
Courier à adresser par mail: f.benabid@xlim.fr

Directeur de thèse
F. Benabid
Adresse mail du directeur de thèse : f.benabid@xlim.fr
Téléphone Directeur de thèse : 0555457385

Co-directeur de thèse
F. Gérôme et G. Humbert
Adresse mail du co-directeur de thèse : gerome@xlim.fr et georges.humbert@xlim.fr
Téléphone co-Directeur de thèse : 0555457385
Cofinancement LABEX SigmaLIM demandé : OUI

Justification du cofinancement LABEX
Ce sujet fait parti de la chaire attribuée au Pr. Benabid
Thématique LABEX concernée : Thème 1: Matériaux
Thèse pour Action transverse : OUI

Action transverse concernée et justification
Nouvel axe transverse d’Xlim: GPPMM


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