A Xylophone Configuration for a third Generation Gravitational Wave Detector

Achieving the demanding sensitivity and bandwidth, envisaged for third generation gravitational wave (GW) observatories, is extremely challenging with a single broadband interferometer. Very high optical powers (Megawatts) are required to reduce the quantum noise contribution at high frequencies, while the interferometer mirrors have to be cooled to cryogenic temperatures in order to reduce thermal noise sources at low frequencies. To resolve this potential conflict of cryogenic test masses with high thermal load, we present a conceptual design for a 2-band xylophone configuration for a third generation GW observatory, composed of a high-power, high-frequency interferometer and a cryogenic low-power, low-frequency instrument. Featuring inspiral ranges of 3200Mpc and 38000Mpc for binary neutron stars and binary black holes coalesences, respectively, we find that the potential sensitivity of xylophone configurations can be significantly wider and better than what is possible in a single broadband interferometer

Mechanical loss in state-of-the-art amorphous optical coatings

We present the results of mechanical characterizations of many different high-quality optical coatings made of ion-beam-sputtered titania-doped tantala and silica, developed originally for interferometric gravitational-wave detectors. Our data show that in multi-layer stacks (like high-reflection Bragg mirrors, for example) the measured coating dissipation is systematically higher than the expectation and is correlated with the stress condition in the sample. This has a particular relevance for the noise budget of current advanced gravitational-wave interferometers, and, more generally, for any experiment involving thermal-noise limited optical cavities.Comment: 31 pages, 14 figure

Élaboration et mise en oeuvre de couches minces organo-silicates synthétisées par voie sol-gel (application à l'interconnexion optique)

Bien que les interconnexions optiques sur de longues distances soient supplantées depuis longtemps par leurs homologues électriques, la fabrication tout optique d'interconnexions sur courtes distances n'a pas encore été achevée en raison de la difficulté à les intégrer de manière simple et rentable sur des cartes de circuits imprimés. Les structures de couplage sont les éléments clés de ces dispositifs d'interconnexion sur courtes distances car d'une part elles peuvent limiter significativement l'efficacité globale des composants et d'autre part, représentent la majeure partie de leur prix. De par leur taille et poids réduits, les coupleurs à réseaux jouent un rôle important dans la miniaturisation des systèmes. Ils ont également l'avantage d'être compatibles avec les technologies planaires existantes ainsi qu'avec une production en série. Dans ce manuscrit, nous proposons de fabriquer et de caractériser un démonstrateur tout optique comprenant 2 réseaux résonnants agissant comme les portes d'entrée et de sortie de la lumière propagée dans un guide d'ondes multimode. Son design est original et permet théoriquement d'atteindre une efficacité de 90%. Dans le cadre d'un réseau d'excellence européen en micro-optique (NEMO), nous avons comparé l'efficacité de 2 démonstrateurs fabriqués sur le même principe. Le premier utilise des matériaux commerciaux pour la fabrication des réseaux de diffraction et du guide d'ondes multimode, tandis que le second utilise des matériaux innovants (matériaux hybrides organiques-inorganiques) ainsi que des procédés développés au laboratoire Hubert CurienAlthough optical links have supplanted their electrical counterparis in long distance high rate transmission communications, the predicted transition to all optical interconnections at the board level has not happened yet. One of the reasons is that it turned out to be more difficult than expected to integrate optical interconnections in an easy and cost effective way into or onto a board. In short distance optical interconnaections, coupling structures are key elements as they significantly limit the overall efficiency of the components and represent the major part of the cost of an interconnection circuit. Diffraction grating couplers are bound to play an increasingly important role in miniaturised systems as they bring reduced weight and size, and have the advantage of being compatible with wafer or board scale batch planar manufacturing processes. In this work, the fabrication process and the characterization of a simple coated platform composed of two resonant gratings that allow light propagation in a highly multimode polymer waveguide are described. Its design is original and might enable to theoretically reach 90% efficiency. In the framework of the European network of excellence in Micro-Optic (NEMO), the abilities of two demonstrators fabricated according to the same schema have been compared : one uses commercial materials for the fabrication of diffraction gratings and waveguide whereas another one uses innovating materials and processes developed in the Hubert Curien LaboratoryST ETIENNE-BU Sciences (422182103) / SudocSudocFranceF

Hard UV-curable organo-mineral coatings for optical applications

Organically-modified silicate incorporating various amounts of zirconium precursor was synthesized via a sol-gel route. The material was deposited as thin films on PMMA substrates and densified by UV-curing. Mechanical properties were measured by nanoindentation and data were recorded continuously as a function of the penetration depth during the loading-unloading cycles. Values of hardness and Young modulus were found in the range 340 to 440 MPa and 4 to 6 GPa respectively. It was shown that these values could be tailored by varying the relative amount of zirconium in the layer. The material exhibited a very elastic behaviour that was related to its high degree of cross-linking assessed by infrared spectroscopy. Results were compared with measurements published by various groups on related materials. The mechanical and optical properties of the samples made this class of material promising as hard coatings for optical applications

Submicrometric gratings fabrication from photosensitive organo-silica-hafnia thin films elaborated by sol-gel processing

International audienceThe aim of this study is the elaboration of a high index sol-gel material in order to prepare submicrometric grating. The gratings were obtained after few seconds of UV exposure in one step using an organically modified silica-hafnia matrix. The chemical composition of thin films after UV and annealing treatments were studied using Fourier Transform Infrared Spectroscopy and X-Ray Photoelectron Spectroscopy. The study of optical properties revealed that the annealed films are transparent from 200 to 1000 nm and have a refractive index from 1.550 to 1.701 depending on the hafnium concentration

High efficiency diffraction grating coupler for low cost optical interconnect

The original device presented in this paper is designed for coupling a free space optical wave under quasi-normal incidence in- and out of- a highly multimode waveguide with minimum losses. It uses two resonant diffraction gratings at the substrate-waveguide interface that are made of a shallow metal grating, covered with a high refractive index layer. It is shown that the resonant structure can theoretically diffract up to 90 % of the incident energy in and out of the waveguiding layer. The geometrical parameters of the structure and the tolerances can easily be achieved by conventional technology means