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 telecommun ication. Visible and infrared multi-aperture interferometry requires many o ptical functions (spatial filtering, beam combination, photometric calibrat ion, polarization control) to detect astronomical signals at very high angu lar resolution. Since the 80's, integrated optics on planar substrate have become available for telecommunication applications with multiple optical f unctions like power dividing, coupling, multiplexing. etc. We present the c oncept 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 stab ility, 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 inexp ensive compared to devices that have the same functionalities in bulk optic s. We think integrated optics will fundamentally change single-mode interfe rometry. Integrated optics devices are in particular well-suited for interf erometric combination of numerous beams to achieve aperture synthesis imagi ng or for space-based interferometers where stability and a minimum of opti cal alignments are wished.