Multi-axial nulling interferometry: demonstration of deep nulling and investigations of polarization effects

The ESA-Darwin mission is devoted to direct detection and spectroscopic characterization of earth-like exoplanets in the thermal infrared domain by nulling interferometry in space. This technique yields the rejection of starlight so as to make detectable the faintly emitting planet in the neighborhood. In that context, Alcatel Alenia Space has developed a nulling breadboard for ESA in order to perform the rejection of an unresolved on-axis source. This device, the Multi Aperture Imaging Interferometer (MAII) demonstrated high rejection capability at a relevant level for exoplanets, in single-polarized and mono-chromatic conditions. In this paper we report on our late investigations using the MAII focussed on modal filtering. The dependence of the nulling ratio on the degeneracy of the guided modes in the modal filter is put into evidence.