Recombineurs Actifs en Niobate de Lithium pour l’Interférométrie Stellaire – RALIS

One of the main activities in Astronomy is the detection of exoplanets and the study of planet formation inside the dusk disk around a host star. In order to allow observation within the disk, infrared observations are a good option since they give access to cool matter studies, where optical (visible) observation is blocked by the absorption of interstellar dust. In particular, the L-band atmospheric transmission window (3.4-4.1 um) presents promising features for astrophysical studies (i.e. cool matter emission and terrestrial exoplanet detection). Nulling interferometry, considered among other techniques for exoplanet detection by space agencies and research laboratories, is at the heart of several instruments like ALADDIN (Antarctic L-Band Astrophysics Discovery Demonstrator for Interferometric Nulling), the nuller interferometer of LBTI (under construction at University of Arizona) and PERSEE (laboratory breadboard for PEGASE). PEGASE, the CNES spacecraft-instrument dedicated to spectrometry of hot jupiters and brown dwarfs from 2.5-5 microns, performing a 10-4 nulling, will achieve modal filtering with single mode fibers and bulk optics beam combination separately. All of these instruments are conceived in bulk optics, but there are several advantages pointing towards integrated optics interferometry, first of which the compactness and robustness of an integrated nuller. The lack of materials featuring single-mode channel waveguides in the L-band, compulsory to realize efficient mode filtering, has limited the development of concepts similar to integrated interferometers already obtained in the J, H and K bands. Our goal is to develop an integrated optics beam combiner, consistent with PEGASE nulling requirements, based on Lithium Niobate (LiNbO3) a transparent material in the L-band. Our goal is to achieve 10-4 nulling, photometry and mode filtering in a single, compact and light device. This should increase the robustness of the beam combiners, and relax the constraints in stability. LiNbO3 brings the advantages of a suitable transparency over the L-band together with excellent electro-optical properties that allow accurate active control of the phases and intensities on the incoming beams. As a recent research team at LAOG (Laboratoire d'Astrophysique de Grenoble) we propose, together with our collaborators of FEMTO-ST (Besançon), to develop LiNbO3-based high precision active nullers in the L-band. This project aims at manufacturing integrated optics beam combiners that could attain optical extinction over -40dB (10-4) between the two arms of a Mach-Zehnder interferometer. This project will be leaded by Guillermo Martin, recruited in September 2006 as Associate Professor at LAOG. His experience in active waveguide realizations, LAOG expertise in astrophysics (especially in stellar and planetary formation) as well as infrared waveguide characterizations, and FEMTO-ST technological abilities with LiNbO3, will ensure the optimal development of the project.