4 Conclusion and future prospects

We have obtained first high-contrast white-light interferograms with an off-the-shelves integrated optics component used as a two aperture beam combiner. The high and stable contrasts as well as the high optical throughput validate our approach for combining stellar beams by means of integrated optics presented in Paper I.

This preliminary analysis requires further characterizations and improvements. The importance of dispersion, birefringence and other phenomena in the fibers and in the components have to be fully understood. For this purpose, two-way beam combiners optimized for astronomy are under characterization (spectroscopic and polarimetric measurements for instance) in order to carefully control their optical properties. A complete description of optical and interferometric properties of integrated optics component will be presented in a forthcoming Paper [Haguenauer et al. (1999)]. The optical fibers should maintain polarization to avoid specific contrast losses and have optimized lengths to avoid chromatic dispersion. This experimental precaution is decisive to achieve image reconstruction [Delage (1998)].

Our research program is based on the study of new integrated optics technologies for long baseline interferometry in the infrared, and, the design of beam combiners for multiple apertures (see Paper I). Some specific beam combiners will then be eventually used in a scientific instrumental prototype on astronomical interferometers. Preliminary tests on the GI2T/Regain interferometer [Mourard et al. (1998)] will be carried out with the Integrated Optics Near-infrared Interferometric Camera (IONIC) prototype [Berger et al. (1998)].

Acknowledgements

We would like to warmly thank E. Le Coarer for his precious support in instrument control. We thank the referee, Dr. Shaklan, for a careful reading of our paper and for suggestions which helped to improve its content. The work was partially funded by PNHRA/INSU, CNRS/Ultimatech and DGA/DRET (Contract 971091). The integrated optics components have been manufactured and fiber-connected by the GeeO company.