Multiple-aperture optical telescopes: cophasing sensor testbed

The goal of a cophasing sensor (CS) is to measure the phase disturbances between the sub-apertures or inside each aperture of a telescope. Three CSs are currently studied at ONERA. A first CS for Earth imaging is based on phase diversity on extended sources (cf companion paper by L. Mugnier). A second CS for intercalibration uses phase retrieval on a point source. The third CS for nulling interferometry (“DWARF”, for the ESA/DARWIN mission) is based on similar algorithms. To test performance of these CSs, ONERA has defined and integrated a multipurpose bench, “BRISE”. Its main features are the simultaneous imaging of a point source and of an extended source, the minimisation of absolute and differential disturbances, the use of any aperture configuration and the generation of pure calibrated piston/tip/tilt aberrations on three sub-apertures by a dedicated PZT-based device. Preliminary experimental results are consistent with numerical simulations and confirm nanometric performance.