Integrated optics for astronomical interferometry - II. First laboratory white-light interferograms

We report first white-light interferograms obtained with an integrated optics beam combiner on a glass plate. These results demonstrate the feasability of singlemode interferometric beam combination with integrated optics technology presented and discussed in Paper I (Malbet et al. 1999). 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.