Comparison of beam combiners for a synthetic aperture imaging telescope

Future astronomical space missions will comprise a constellation of several optical telescopes to detect exo-planets by interferometric nulling of starlight. The Darwin mission of the European Space Agency (ESA) and NASAs Terrestrial Planet Finder Interferometer both consist of a free-flying collection of telescopes and a beam combiner. As such, the constellation provides a co-phased array of telescopes that can also be used for aperture synthesis imaging. This imaging technique relies on recording intensity interference patterns, in which the layout of the beam combination optics and the detector play a key role. Several designs for beam combination have been proposed in the literature. In this article, we compare these beam combiners by rigorously simulating the imaging process of a weak stellar source, taking into account the photon arrival statistics, an imperfect detection process and the image reconstruction from the recorded data. The results are presented as the to be expected reconstruction error in the luminous intensity distribution function of a wide-field stellar source versus the provided amount of photons. Using these results, the optimum design of the combination beam combiner and detector array can be identified.