Study of a new cophasing system for hypertelescopes

As the next generation of giant optical interferometers, hypertelescopes will provide high resolution direct imaging of celestial sources by using the densification principle.1 In order to determine the technical requirements of such an instrument, an interferometric testbench, called SIRIUS (Patru et al. 2004), has been developed at the Observatoire de la Cote d'Azur, France. The active cophasing of the beams remains the most significant hard point to preserve the quality of the image. It has been shown that this cophasing should be at the level of λ/10 so that more than 90% of the energy remains in the central peak of the point spread function.2 In the current version of SIRIUS, the raw coherencing is done manually by adjusting air delay lines, whereas the cophasing is ensured by a fibered cophasing system. We present our study of an optimized cophasing system that we intend to develop on the SIRIUS testbench. One of the main goals is to be adaptable to any interferometer, whatever the configuration of the entrance pupil and the number of sub pupils. This new version will improve the cophasing system by using a derived version of the dispersed speckles method3 for fine cophasing. The observed images will then be stabilized during a longer period, allowing a more efficient analysis of the studied source.