Integrated optics for astronomical interferometry. III. Optical validationof a planar optics two-telescope beam combiner

The optical characterization of a fiber-connected planar optics beam combin er dedicated to astronomical interferometry for two telescopes is presented . The beam combiner, fully integrated on a single 5 mm x 40 mm glass chip, is tested as the central part of an astronomical instrument. The single-mod e waveguides are made by silver-ion-exchange technology upon glass substrat es and provide spatial filtering, which improves the visibility measurement accuracy by selecting only the fundamental mode of the beams at the telesc ope focal plane. A global optical throughput of 43% is measured, and the so urces of losses are identified and examined in detail. Solutions for improv ing this throughput are proposed. High and stable contrasts are obtained wi th a 1.55-mu m laser diode (greater than or similar to 96%) and with a whit e-light source (similar to 92%) in the astronomical H filter (1.43 mu m; 1. 77 mu m). The need for accurate control of differential instrumental polari zation is demonstrated. In this context the intrinsic polarization-maintain ing property of the planar optics component is characterized. This validati on of the important potential uses of integrated planar optics should be va luable for future design of optical telescope arrays. (C) 2000 Optical Soci ety of America.