Xavier Rejeaunier

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.

Dispersion-managed fiber with low chromatic dispersion slope

A dispersion-balanced fiber exhibiting a low chromatic dispersion slope (<0.015 ps/nm/sup 2//km at 1550 nm) was obtained by longitudinally changing the radial dimension of a refractive index profile. We report theoretical and experimental results and trade-offs between effective-area and cable ability aspects.

Multi-axial interferometry: demonstration of deep nulling

The ESA-Darwin mission is devoted to direct detection and spectroscopic characterization of earthlike exoplanets. Starlight rejection is achieved by nulling interferometry from space 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 demonstrate in laboratory conditions the rejection of an on-axis source. This device, the Multi Aperture Imaging Interferometer (MAII) demonstrated high rejection capability at a relevant level for exoplanets, in singlepolarized and mono-chromatic conditions. In this paper we report on the new multi-axial configuration of MAII and we summarize our late nulling results.

Programmable spectrometer using MOEMs devices for space applications

A new class of spectrometer can be designed using programmable components such as MOEMS which enable to tune the beam in spectral width and central wavelength. It becomes possible to propose for space applications a spectrometer with programmable resolution and adjustable spectral bandwidth. The proposed way to tune the output beam is to use the diffraction effect with the so-called PMDG (Programmable Micro Diffraction Gratings ) diffractive MEMS. In that case, small moving structures can form programmable gratings, diffracting or not the incoming light. In the proposed concept, the MOEMS is placed in the focal plane of a first diffracting stage (using a grating for instance). With such implementation, the MOEMS component can be used to select some wavelengths (for instance by reflecting them) and to switch-off the others (for instance by diffracting them). A second diffracting stage is used to recombine the beam composed by all the selected wavelengths. It becomes then possible to change and adjust the filter in λ and Δλ. This type of implementation is very interesting for space applications (Astronomy, Earth observation, planetary observation). Firstly because it becomes possible to tune the filtering function quasi instantaneously. And secondly because the focal plane dimension can be reduced to a single detector (for application without field of view) or to a linear detector instead of a 2D matrix detector (for application with field of view) thanks to a sequential acquisition of the signal.

Dark fringe interferometry: Multi-beam configuration of the Alcatel nulling interferometer MAII and recent results

Direct detection and spectroscopic characterization of earth-like exoplanets require to eliminate the starlight in the recorded signal at a rejection level (collected flux / residual flux) around 10 in the thermal infrared domain. Another need is to reach angular resolution in the range 0.1 to 0.01 arcsec. In this context, nulling interferometry is recognized as the preferred instrumental approach. In the framework of the ESA-Darwin mission, preliminary studies for nulling systems have been initiated, the prime goal to achieve being mastering nulling process. In this purpose, Alcatel Space has developed a nulling test-bench, operating in near infrared (1.55 μm), not only to demonstrate capability of obtaining an appropriate rejection level but also to study and characterize the use of emerging techniques. The Darwin system will ultimately benefit from these results. In this paper, we report the most recent configuration of the Alcatel Space nulling breadboard which uses the multi-beam recombination technique, current baseline for Darwin. The results obtained with this version shows rejection performance at nearly 10 (stable level) with a polychromatic source (λ = 1.55 μm, ∆λ= 80 nm).