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.
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.
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.
In the context of the ESA-Darwin mission, Thales Alenia Space has developed a nulling breadboard for ESA. The Multi
Aperture Imaging Interferometer (MAII) first demonstrated deep nulling in both integrated optics and multi-axial
combination schemes.
More recently, Thales Alenia Space and Observatoire de la Côte d'Azur have been improving the nulling performance of
MAII. The work was focused on polarization and the bench was upgraded consequently. Unpolarized and polarized
nulling ratios are now quite similar at N ≈ 10-5 over a 5% relative bandwidth, stable over more than one hour.
In this paper, we report on the improvements we have implemented in MAII and present our latest results.
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.
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