Christophe Buisset, Xavier Rejeaunier, Yves Rabbia, Cyril Ruilier, Marc Barillot , Josep Maria Perdigues Armengol, and Lars Lierstuen
MULTI-AXIAL NULLING INTERFEROMETRY: DEMONSTRATION OF DEEP NULLING AND INVESTIGATIONS OF POLARIZATION EFFECTS. (Poster)

MULTI-AXIAL NULLING INTERFEROMETRY: DEMONSTRATION OF DEEP NULLING AND INVESTIGATIONS OF POLARIZATION EFFECTS.

Christophe Buisset(1,2), Xavier Rejeaunier(1), Yves Rabbia(2), Cyril Ruilier(1), Marc Barillot(1) , Josep Maria Perdigues Armengol(3), and Lars Lierstuen(4)
(1) Alcatel Alenia Space, Cannes, France.
(2) Observatoire de la Côte dAzur, Grasse, France.
(3) ESA-ESTEC, Noordwijk, The Netherlands.
(4) Kongsberg Defense and Aerospace, Kongsberg, Norway.

A major goal of the ESA Darwin mission is to provide data in the infrared from which it will be possible to evaluate evidence of life. After observations aiming at detecting planets around stars, spectroscopic observations will try to put in evidence presence of spectral lines of chemical elements considered as reliable indicators of life. Nulling interferometry is the technique chosen for that purpose. The Darwin mission requires stable starlight rejection to an efficiency around $10^{6}$ over the whole spectral band. MAI$^{2}$ (Multi Aperture Imaging Interferometer) is a nulling laboratory breadboard developed by Alcatel Alenia Space in the frame of technical developments funded by ESA for Darwin. Deep extinction ratio capability has already been reported with this bench in single-polarized and mono-chromatic conditions using coaxial integrated optics beam combination. In this paper we report on the experimental verification of deep nulling based on multiaxial beam combination on MAI$^{2}$, for which the breadboard was modified and optimized. Nulling depth results at the $10^{5}$ level using a polychromatic source ($\Delta$$\lambda$/$\lambda$$\sim$5%) are presented with both the co-axial and multi-axial beam combination schemes. Rejection ratios but also stability have been greatly improved with respect to the former configuration of the bench. Furthermore, this bench enabled us to investigate the coupling into the modal filter in the multiaxial beam combination configuration, in the frame of the Fibre Optic Wavefront Filtering (FOWF) technological activity led by Kongsberg under ESA contract 18772. Particular efforts were made at the polarization level. Results are discussed in this paper. Finally we briefly present the next experimental steps involving MAI$^{2}$.