Test de mini-résonateurs optiques pour le filtrage et la stabilisation de sources hyperfréquences

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Microwave filtering using high Q optical resonators

session EuMC20 " Microwave Photonics " [EuMC20-4], http://www.eumweek.com/2008/A technique is described to implement a microwave filtering approach based on optical resonators. This technique involves the laser stabilization onto a resonator mode, and the use of the two lateral sidemodes for RF or microwave filtering. The Q enhancement compared to the classical non-coherent optical delay line technique is high, and the equivalent microwave Q overcome the best microwave resonators, at least in the upper microwave range

Optical Microresonators used for Stabilisation and Miniaturisation of High Spectral Purity Microwave Sources for Space Applications

International audienceThe use of optical resonators for microwave oscillator stabilization is discussed in this paper. This recently proposed approach could be a disruptive technology, in a near future, giving access to high performance in a small volume thanks to the extremely high optical Q factor and to the small dimensions of the optical resonator. Many topologies can be chosen for the electrical-optical oscillator (OEO), and many different approaches can be investigated for the resonator itself, and the coupling techniques. This paper gives an overview of all these techniques, together with some preliminary results on a dedicated resonator measurement bench

A characterization bench to analyse various types of optical WGM resonators for high spectral purity microwave sources applications

International audienceWe have set up a characterization bench to test the optical and microwave properties of high Q optical whispering gallery mode resonators. The bench comprises nanometer scale precision 3D displacement stages mounted on an anti-vibration table in order to get a very fine coupling between the optical resonator and the tapered fibers used for coupling. This bench can be adapted to different types of resonators: μ- and mmspheres of SiO2 or monocrystalline disks. In this paper we present several approaches which have been investigatedin order to test these resonators. Different types of optical sources have been used: a broadband 'white light' source around 1550 nm, a T-control free-running laser emitting at ~1550 nm, an external cavity laser with a narrow spectral width. We have also performed a temperature control of the sphere. Finally, we are trying to lock the laser on a sphere optical mode in order to get a stable system

Sources hyperfréquences à haute pureté spectrale à base de micro-résonateurs

diffusion restreintephase d'évaluation - Rapport 1La première partie du rapport débute par un rapide historique des oscillateurs micro-ondes à base de lignes à retard optique. Puis, le problème du remplacement de la ligne à retard par un résonateur optique est traité en détail. Un second chapitre est en effet consacré aux résonateurs, puis un troisième aux oscillateurs basés sur ces résonateurs. Ensuite, la deuxième partie du rapport est consacrée aux travaux en cours. Il est exposé les problèmes liés à la métrologie de ces sources à très haute pureté spectrale. Là encore, l'introduction de l'optique devrait permettre une amélioration importante des performances des bancs de mesure de bruit de phase. Puis, une description de la fabrication des résonateurs optique est donnée. Enfin, le dernier chapitre est consacré au projet

Sources hyperfréquences à très haute pureté spectrale à base de mini-résonateurs optique

phase de développement - Rapport 3 (T0+18)Ce rapport est le troisième rapport à six mois du contrat " Sources hyperfréquences à très haute pureté spectrale à base de mini-résonateurs optique : phase de développement ", impliquant le LAAS-CNRS Toulouse, FEMTO-ST Besançon et l'ENSSAT Lannion. Il s'agit donc du rapport à mi-parcours de cette action de trois ans. Il est structuré autour des différentes tâches et sous-tâches définies lors de l'établissement de l'action contractuelle. Le travail mené par les trois laboratoires progresse aujourd'hui rapidement sur plusieurs fronts : celui du résonateur (conception, réalisation, caractérisation), mais aussi celui des oscillateurs fibrés (réalisation, modélisation). En ce qui concerne le résonateur, nous sommes aujourd'hui capables de caractériser le coefficient de qualité, nous proposons des pistes pour la stabilisation des dérives en température. La qualité des réalisations de résonateurs s'améliore, et le nombre et la variété des composants disponibles pour cette étude est aujourd'hui relativement important. En ce qui concerne les problèmes de bruit dans les oscillateurs optiques, plusieurs techniques différentes et complémentaires développées dans les laboratoires impliqués dans ces tâches sont proposées et testées. Nous sommes donc très proches du système final : l'oscillateur à résonateur optique

Sources hyperfréquences à très haute pureté spectrale à base de mini-résonateurs optique

phase de développement - Rapport 3 (T0+18)Ce rapport est le troisième rapport à six mois du contrat " Sources hyperfréquences à très haute pureté spectrale à base de mini-résonateurs optique : phase de développement ", impliquant le LAAS-CNRS Toulouse, FEMTO-ST Besançon et l'ENSSAT Lannion. Il s'agit donc du rapport à mi-parcours de cette action de trois ans. Il est structuré autour des différentes tâches et sous-tâches définies lors de l'établissement de l'action contractuelle. Le travail mené par les trois laboratoires progresse aujourd'hui rapidement sur plusieurs fronts : celui du résonateur (conception, réalisation, caractérisation), mais aussi celui des oscillateurs fibrés (réalisation, modélisation). En ce qui concerne le résonateur, nous sommes aujourd'hui capables de caractériser le coefficient de qualité, nous proposons des pistes pour la stabilisation des dérives en température. La qualité des réalisations de résonateurs s'améliore, et le nombre et la variété des composants disponibles pour cette étude est aujourd'hui relativement important. En ce qui concerne les problèmes de bruit dans les oscillateurs optiques, plusieurs techniques différentes et complémentaires développées dans les laboratoires impliqués dans ces tâches sont proposées et testées. Nous sommes donc très proches du système final : l'oscillateur à résonateur optique

SIZE RESOLVED DUST EMISSION FLUXES MEASURED BY THE GRADIENT METHOD DURING 6 DUST STORMS OF THE WIND-O-V's 2017 EXPERIMENT IN SOUTHERN TUNISIA

International audienceDust size distribution is a critical parameter to understand the interactions of mineral dust with its environment throughoutits life cycle [1]. This is why it is important to document this characteristic of mineral dust from emission to deposition,included the atmospheric transport phase. Until recently, because of the limitation of the available instrumentation, onlythe total dust mass flux could be measured at emission, and this with a limited (half hourly at best) temporal resolution.The development of optical particle counters has allowed overcoming this limitation and the dust size distributions cannow be measured at high frequency.Using a dedicated experimental setup, size resolved dust emission fluxes were documented on a bare plot in southernTunisia in the framework of the first intensive observing period of the WIND-O-V (WIND erOsion in presence ofVegetation) program (grant ANR-15-CE02-0013). The experiment was conducted from 1 March to 15 May 2017 in theDar Dhaoui Experimental Range of the Institut des Régions Arides of Médenine. Size resolved dust emission fluxes werecomputed using the gradient method [2] and using for the first time WELAS optical particle counters.During the field campaign, 6 dust storms were sampled. In the present work, the size resolved dust emission fluxesmeasured during the dust storms are presented and discussed in relation with the meteorological characteristics of thestorms and the characteristics of the soil surface

The WIND-O-V field experiment: WIND erOsion in presence of sparse Vegetation

International audienceWind erosion in semiarid areas is a major threat for the soil productivity as it impoverishes soil in organic matters and nutrients. Compared to desert regions, these regions are characterized by sparse seasonal vegetation that impacts the erosion process. Semiarid areas face two major evolutions that may modify their wind soil erosion in the future: (1) climate change, with a modification of the amplitude and frequency of precipitations, affecting the surface vegetation cover, and (2) population growth, generating a considerable human pressure on the land use. Characterizing wind erosion in such complex regions is, therefore, crucial and challenging. In order to better predict the amount and composition of emitted dust from semiarid areas, a novel field experiment named WIND-O-V (wind erosion in presence of sparse vegetation) has been performed in 2017 and 2018 in South Tunisia. The originality of this experiment is (1) to cover successively a plot without and with sparse vegetation, and (2) to combine detailed measurements of wind dynamics (including turbulence), size-resolved saltation and dust fluxes, and erosion-flux compositional fractionation along the soil-saltation-suspension continuum. The experiment took place from March to May in the experimental range of the Institut des Régions Arides (IRA) of Médenine (Dar Dhaoui, 25 km east of Médenine). The site approximates a flat half-circle plot of 150 m radius where measurements were performed at the center of the circle in order to ensure a fetch of at least 150 m. In 2017, the surface has been tilled with a disc plough and levelled with a wood board in order to meet the conditions of an ideal flat bare soil without soil crust or ridges. In 2018, sparse vegetation consisting of barley tufts have been grown on the plot with a 3.3 m wide regular arrangement. Three types of measures were carried out. Meteorology: on a 9 m high mast erected at the center of the plot, turbulent velocity components and air temperature fluctuations were measured simultaneously at 1.0, 1.9, 3.0, and 4.1 m height using four 3D sonic anemometers sampling at 60, 50, 50, and 20 Hz, respectively. On the same mast, 7 cup anemometers (0.2, 0.6, 1.3, 1.8, 3.0, 4.0, 5.2 m) and 4 thermocouples (0.4, 1.6, 3.7, 5.0 m) were also installed to measure simultaneously at 0.1 Hz the mean horizontal wind velocity and temperature profiles, respectively. Three additional 2D sonic anemometers were installed in 2018 around a barley tuft to characterize the wind around the vegetation. Roughness length of the surface and friction velocity were computed on the bare plot case by comparing the Law-of-the-wall and Eddy-Covariance methods. Saltation flux: one vertical array of 5 sediment traps like Big Spring Number Eight (BSNE) was deployed to quantify the saltation flux and its size distribution. The modified BSNE had a 5 times wider opening area to collect larger sediment quantities, allowing sequential (in time) sampling of individual erosive events and guarantying the possibility of applying size resolved analyses. Saltation flux measurements with a better temporal resolution were thus associated with more stable friction velocity conditions. In 2018, 5 MWAC masts were added to measure the spatial variability of the flux due to the sparse vegetation. A Saltiphone and a camera gave information on the beginning, end, and duration of erosive events. Dust flux: for the first time size-resolved dust fluxes were estimated from both the traditional flux-gradient approach and the eddy covariance approach. For the first approach, mass and size resolved number concentrations were measured at two levels (2 and 4 m). To that purpose, two TEOM microbalances and two optical particle counters (WELAS Promo 2300) were used. Both sensor-types were connected to omnidirectional air sampling inlets. The WELAS monitored at 1 Hz the dust concentrations per size class (32 classes between 0.3 and 17 μm). For the second approach, a third WELAS was coupled to the 3 m high sonic anemometer in order to correlate the size-resolved dust concentration and the vertical wind velocity fluctuations. Finally, the chemical composition of dust fluxes was estimated from the sequential sampling of dust particles at two levels (2 and 4 m) with online filters equipped with inlets of different size cutoffs (20, 10, 2.5 and 1 μm)