Integrated optics for astronomical interferometry. I. Concept and astronomical applications

We propose a new instrumental concept for long-baseline optical single-mode interferometry using integrated optics which were developed for telecommunication. Visible and infrared multi-aperture interferometry requires many optical functions (spatial filtering, beam combination, photometric calibration, polarization control) to detect astronomical signals at very high angular resolution. Since the 80's, integrated optics on planar substrate have become available for telecommunication applications with multiple optical functions like power dividing, coupling, multiplexing, etc. We present the concept of an optical / infrared interferometric instrument based on this new technology. The main advantage is to provide an interferometric combination unit on a single optical chip. Integrated optics are compact, provide stability, low sensitivity to external constrains like temperature, pressure or mechanical stresses, no optical alignment except for coupling, simplicity and intrinsic polarization control. The integrated optics devices are inexpensive compared to devices that have the same functionalities in bulk optics. We think integrated optics will fundamentally change single-mode interferometry. Integrated optics devices are in particular well-suited for interferometric combination of numerous beams to achieve aperture synthesis imaging or for space-based interferometers where stability and a minimum of optical alignments are wished.Comment: 11 pages, 8 figures, accpeted by Astronomy and Astrophysics Supplement Serie

Integrated Laser Doppler Velocimeter for Fluid Velocity and Wall Friction Measurements

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Integrated optics for astronomical interferometry

We report first white-light interferograms obtained with an integrated optics beam combiner on a glass plate. These results demonstrate the feasability of single-mode interferometric beam combination with integrated optics technology presented and discussed in Paper I(). The demonstration is achieved in laboratory with off-the-shelves components coming from micro-sensor applications, not optimized for astronomical use. These two-telescope beam combiners made by ion exchange technique on glass substrate provide laboratory white-light interferograms simultaneously with photometric calibration. A dedicated interferometric workbench using optical fibers is set up to characterize these devices. Despite the rather low match of the component parameters to astronomical constraints, we obtain stable contrasts higher than 93% with a 1.54-μm laser source and up to 78% with a white-light source in the astronomical H band. Global throughput of 27% for a potassium ion exchange beam combiner and of 43% for a silver one are reached. This work validates our approach for combining several stellar beams of a long baseline interferometer with integrated optics components

Integrated optics for astronomical interferometry

We report laboratory and on sky characterizations of planar integrated optics beam combiners in the K ([ 2.0 μm; 2.4 μm] ) and K' ([ 2.02 μm; 2.30 μm] ) bands. Because of the strong scientific interests of the K band, we have extended the integrated optics technologies available in the telecom range (i.e. at 0.8 μm, 1.3 μm and 1.5 μm) to 2.0–2.5 μm. Ion exchange components optimized for these atmospheric bands provide stable contrasts higher than 95% with a laboratory white-light source and global throughputs of 35% in this spectral range. These results are completed with first stellar interferograms obtained with a silica-on-silicon two-way beam combiner on the IOTA interferometer. We characterized in the H and K bands the throughput of this beam combiner optimized for the H band ([ 1.47 μm; 1.78 μm] ). On-sky fringes obtained on ιAur in the H and K' bands clearly demonstrate a high instrumental contrast (larger than 50%) in both bands. This shows that integrated optics works with high performance outside its usual wavelength domain and provides good solutions for astronomical interferometry in a large wavelength range. We have measured single-mode ranges over 1 μm on our components which would allow to observe in two spectral bands simultaneously or to integrate both metrology reference and science signals in a single chip for astrometric applications.

An integrated-optics 3-way beam combiner for IOTA

We report here the first visibility and closure-phase measurements done with the IONIC instrument at the IOTA interferometer. The IONIC instrument is presented and preliminary analysis of the results discussed. Future improvements of IONIC are envisioned