EDP Sciences
Free access
Issue A&A
Volume 498, Number 2, May I 2009
Page(s) 601 - 613
Section Astronomical instrumentation
DOI http://dx.doi.org/10.1051/0004-6361/200811083
Published online 05 March 2009

A&A 498, 601-613 (2009)
DOI: 10.1051/0004-6361/200811083

An integrated optics beam combiner for the second generation VLTI instruments

M. Benisty1, J.-P. Berger1, L. Jocou1, P. Labeye2, F. Malbet1, K. Perraut1, and P. Kern1

1  Laboratoire d'AstrOphysique de Grenoble (LAOG), 414 rue de la piscine, 38400 Saint-Martin d'Hères, France
    e-mail: Myriam.Benisty@obs.ujf-grenoble.fr
2  CEA-LETI, Minatec, 17 rue des martyrs, 38054 Grenoble, France

Received 3 October 2008 / Accepted 28 January 2009

Abstract
Context. Recently, an increasing number of scientific publications making use of images obtained with near-infrared long-baseline interferometry have been produced. The technique has reached, at last, a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arc-second model-independent imaging. The Very Large Telescope Interferometer (VLTI) will soon be equipped with instruments able to combine between four and six telescopes.
Aims. In the framework of the VLTI second generation instruments Gravity and VSI, we propose a new beam combining concept using integrated optics (IO) technologies with a novel ABCD-like fringe encoding scheme. Our goal is to demonstrate that IO-based combinations bring considerable advantages in terms of instrumental design and performance. We therefore aim at giving a full characterization of an IO beam combiner in order to establish its performance and check its compliance with the specifications of an imaging instrument.
Methods. For this purpose, prototype IO beam combiners have been manufactured and laboratory measurements were made in the H band with a dedicated testbed, simulating a four-telescope interferometer. We studied the beam combiners through the analysis of throughput, instrumental visibilities, phases and closure phases in wide band as well as with spectral dispersion. Study of the polarization properties was also carried out.
Results. We obtain competitive throughput (65%), high and stable instrumental contrasts (from 80% in wide band up to 100% $\pm$ 1% with spectral dispersion), stable but non-zero closure phases (e.g. 115° $\pm$ 2°) which we attribute to internal optical path differences (OPD) that can be calibrated. We validate a new static and an achromatic phase shifting IO function close to the nominal 90° value (e.g. 80° $\pm$ 1°). All these observables show limited chromaticity over the H band range.
Conclusions. Our results demonstrate that such ABCD-like beam combiners are particularly well suited for interferometric combination of multiple beams to achieve aperture synthesis imaging. This opens the way to extending this technique to all near infrared wavelengths and in particular, the K band.


Key words: instrumentation: interferometers



© ESO 2009

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)