References of "Loicq, Jerôme"
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See detailDevelopment of a space spectropolarimeter for full Stokes parameters retrieval
Vasilescu, Bogdan ULiege; Nazé, Yaël ULiege; Rauw, Grégor ULiege et al

in International Conference on Space Optics — ICSO 2020 (2021, June 11)

This paper presents the firsts steps of the development of a new spectropolarimeter with a high potential for space applications. The instrument, designed on birefringent elements, avoids the need for ... [more ▼]

This paper presents the firsts steps of the development of a new spectropolarimeter with a high potential for space applications. The instrument, designed on birefringent elements, avoids the need for rotating elements and may cover the entire Stokes vector on a large wavelength band. In addition, the architecture of the modulator enables a very high polarimetric efficiency, placing this concept above classical spectropolarimeters. A new proof for the solution uniqueness is presented, and base on that, a thorough analysis of the polarimetric efficiency. [less ▲]

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See detailFeasibility study of an interferometric Small-Sat to study exoplanets
Dandumont, Colin ULiege; Defrere, Denis ULiege; Loicq, Jerôme ULiege

in Proceedings of SPIE: The International Society for Optical Engineering (2021, June 11), 11852

One of the main goals of exoplanet science is to characterize the atmosphere of rocky exoplanets in the habitable zone of nearby stars. A space-based nulling interferometry, observing in the mid-infrared ... [more ▼]

One of the main goals of exoplanet science is to characterize the atmosphere of rocky exoplanets in the habitable zone of nearby stars. A space-based nulling interferometry, observing in the mid-infrared (3-20 μm), is considered to be one of the most promising solutions to tackle this observing challenge. The LIFE project, a free-flying space-based mid-infrared nulling interferometer, would have this capability. However, several key technologies need to be demonstrated before launching such an ambitious mission. A small space-based mission can be considered as a useful prerequisite. In this paper, we consider three small satellite architectures, two CubeSats, and a PROBA-like satellite. Based on a Bracewell architecture and without free-flying, these monolithic satellites can demonstrate some key components like the null capability and its stability on real targets. The achromatic phase shifter needs also to be demonstrated in space. Based on the scientific capabilities and exoplanet detection yield of these architectures, optical constraints are derived (pointing stability, and optical path difference correction). Orbital simulations, exploring a range of classical orbits for such a satellite, are also discussed. [less ▲]

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See detailMaking compact and innovative dual-band thermal imagers using hybrid optical elements
Laborde, Victor ULiege; Loicq, Jerôme ULiege; Habraken, Serge ULiege et al

Scientific conference (2021, April 01)

Infrared (IR) remote sensing o ers a huge range of applications, mostly addressing make-or-break issues of our century (crops water content monitoring, forest res and volcanic eruption detection and ... [more ▼]

Infrared (IR) remote sensing o ers a huge range of applications, mostly addressing make-or-break issues of our century (crops water content monitoring, forest res and volcanic eruption detection and imaging, etc.). These applications fall under di erent spectral bands, known as mid and long-wave infrared, which are very hard to combine in a single compact instrument. In this article we propose to explore the infrared (IR) behaviour of a dual-band di ractive component: the multilayer di ractive optical element (MLDOE). We use and discuss the thin element approximation as a valid phase model. Using Fourier optics, we are able to simulate the resulting image of the MLDOE. Thereby, ray-tracing software are not accurate to model a complex di ractive component. The Strehl ratio is used to determine the focalization e ciency for the working order, which is above 95% in the mid and long-wave infrared bands. This result, along with the very low energy content of the other orders, proves the strong imaging potential of MLDOEs for dual-band applications. It is also demonstrated that the MLDOE has the same chromatic behaviour as standard DOEs, making it a very useful component for infrared achromatization. [less ▲]

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See detailModeling infrared behavior of multilayer diffractive optical elements using Fourier optics
Laborde, Victor ULiege; Loicq, Jerôme ULiege; Habraken, Serge ULiege

in Applied Optics (2021), 60(7), 2037-3045

In this paper, we propose to explore the infrared (IR) behavior of multilayer diffractive optical elements (MLDOEs). IR MLDOEs are designed for the development of space instruments dedicated to Earth ... [more ▼]

In this paper, we propose to explore the infrared (IR) behavior of multilayer diffractive optical elements (MLDOEs). IR MLDOEs are designed for the development of space instruments dedicated to Earth observation. The phase effect of the MLDOE on a paraxial plane wave is studied using exact kinoform shapes for each layer. The modeling of the optical path difference uses thin element approximation. Until now, MLDOEs have been designed and simulated on ray-tracing software with binary diffractive layers. In this study, after passing through the MLDOE, the field is propagated using a method that utilizes the angular spectrum of plane waves. The Strehl ratio is used to determine the “best focus” plane, where it is shown that the focalization efficiency is above 95% for the working order in the mid- and long-wave IR bands. This result, along with the very low energy content of the other orders, proves the strong imaging potential of MLDOEs for dual-band applications. It is also demonstrated that the MLDOE has the same chromatic behavior as standard DOEs, making it a very useful component for IR achromatization. [less ▲]

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See detailPhotonic Structuration of Hybrid Inverse-Opal TiO2—Perovskite Layers for Enhanced Light Absorption in Solar Cells
Maho, Anthony ULiege; Lobet, Michaël; Daem, Nathan ULiege et al

in ACS Applied Energy Materials (2021)

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See detailVortex phase masks of topological charge 4 and higher with diamond subwavelength gratings
König, Lorenzo ULiege; Absil, Olivier ULiege; Delacroix, Christian ULiege et al

in Navarro, R; Geyl, R (Eds.) Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV (2020, December 13)

High contrast imaging at small inner working angles can be achieved using a vector vortex coronagraph in the focal plane of the telescope providing a helical phase ramp with a singularity at its center ... [more ▼]

High contrast imaging at small inner working angles can be achieved using a vector vortex coronagraph in the focal plane of the telescope providing a helical phase ramp with a singularity at its center. The form birefringence of full-diamond subwavelength gratings has proven to be well suited to manufacture such vortex phase masks for coronagraphic applications (Subwavelength Grating Vortex Coronagraph, SGVC). In the past years our group has developed and manufactured SGVCs of topological charge 2 (Annular Groove Phase Mask, AGPM) made of a concentric diamond subwavelength grating. For future applications including ELT-class telescopes in the near- to mid-infrared that will partly resolve nearby stars, it is however useful to increase the topological charge of the vortex. After shortly reviewing our previous attempts at optimizing the grating structure for SGVC of charge 4, we present the first laboratory results obtained with such devices. We then introduce and discuss more realistic simulations compared to prior studies using finite-difference time-domain methods. The quality of the simulation results obtained with the open source software MEEP for an AGPM is shown to be appropriate for developing and assessing the performance of future vortex phase masks. We therefore perform updated simulations for SGVC of charge 4 including various designs with straight and curved grating lines. We conclude with a perspective on the potential of metasurfaces and their applications to design novel vortex coronagraphs based on subwavelength structures. [less ▲]

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See detailDevelopment of a space spectropolarimeter for full Stokes parameters retrieval.
Vasilescu, Bogdan ULiege; Nazé, Yaël ULiege; Loicq, Jerôme ULiege

in Proceedings of SPIE: The International Society for Optical Engineering (2020, December 13), 11451

This paper presents recent advancements in the study of a new concept of space spectropolarimeter. The instrument, based on a triple prismatic structure from a birefringent material, avoids the need of ... [more ▼]

This paper presents recent advancements in the study of a new concept of space spectropolarimeter. The instrument, based on a triple prismatic structure from a birefringent material, avoids the need of rotating components and may cover the entire Stokes vector for a very broad wavelength band. The analysis of the concept in noise-free conditions has proved its consistency. Further simulations for different geometries of the modulator are presented. The results allow identifying critical values for the main parameters. Moreover, the previous analysis of the instrument in noisy conditions is completed with the impact study of the spectral resolution, dimension of pixels and signal to noise ratio. [less ▲]

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See detailPerformance study of interferometric small-sats to detect exoplanets:Updated exoplanet yield and application to nearby exoplanets
Dandumont, Colin ULiege; Kammerer, Jens; Defrere, Denis ULiege et al

in Proceedings of SPIE: The International Society for Optical Engineering (2020, December), 11446

Nulling interferometry is considered as one of the most promising solutions to spectrally characterize rocky exoplanets in the habitable zone of nearby stars. It provides both high angular resolution and ... [more ▼]

Nulling interferometry is considered as one of the most promising solutions to spectrally characterize rocky exoplanets in the habitable zone of nearby stars. It provides both high angular resolution and starlight mitigation. It requires however several technologies that need to be demonstrated before a large interferometry space-based mission flies. A small-sat mission is a good technological precursor. Based on a Bracewell architecture, this unique satellite can demonstrate some key components (null capability, fiber injection, achromatic phase shifter). Scientific capabilities of such a mission are presented. An exoplanet detection yield is derived, and we show that the detection of exoplanets around nearby stars is feasible. [less ▲]

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See detailReview and scientific prospects of high-contrast optical stellar interferometry
Defrere, Denis ULiege; Absil, Olivier ULiege; Berger, J.-P et al

in Proceedings of SPIE: The International Society for Optical Engineering (2020, December), 11446

High-contrast optical stellar interferometry generally refers to instruments able to detect circumstellar emission at least a few hundred times fainter than the host star at high-angular resolution ... [more ▼]

High-contrast optical stellar interferometry generally refers to instruments able to detect circumstellar emission at least a few hundred times fainter than the host star at high-angular resolution (typically within a few \lambda/D). While such contrast levels have been enabled by classical modal-filltered interferometric instruments such asVLTI/PIONIER, CHARA/FLUOR, and CHARA/MIRC the development of instruments able to fi lter out the stellar light has signi cantly pushed this limit, either by nulling interferometry for on-axis observations (e.g., PFN, LBTI, GLINT) or by o -axis classical interferometry with VLTI/GRAVITY. Achieving such high contrast levels at small angular separation was made possible thanks to signi cant developments in technology (e.g., adaptive optics, integrated optics), data acquisition (e.g., fringe tracking, phase chopping), and data reduction techniques (e.g., nulling self-calibration). In this paper, we review the current status of high-contrast optical stellar interferometry and present its key scienti c results. We then present ongoing activities to improve current ground-based interferometric facilities for high-contrast imaging (e.g., Hi-5/VIKING/BIFROST of the ASGARD instrument suite, GRAVITY+) and the scienti c milestones that they would be able to achieve. Finally, we discuss the long-term future of high-contrast stellar interferometry and, in particular, ambitious science cases that would be enabled by space interferometry (e.g., LIFE, space-PFI) and large-scale ground-based projects (PFI). [less ▲]

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See detailPerformance study of interferometric small-sats to detect exoplanets: Updated exoplanet yield and application to nearby exoplanets
Dandumont, Colin ULiege; Kammerer, Jens; Defrere, Denis ULiege et al

Poster (2020, December)

Nulling interferometry is considered as one of the most promising solutions to spectrally characterize rocky exoplanets in the habitable zone of nearby stars. It provides both high angular resolution and ... [more ▼]

Nulling interferometry is considered as one of the most promising solutions to spectrally characterize rocky exoplanets in the habitable zone of nearby stars. It provides both high angular resolution and starlight mitigation. It requires however several technologies that need to be demonstrated before a large interferometry space-based mission flies. A small-sat mission is a good technological precursor. Based on a Bracewell architecture1, this unique satellite can demonstrate some key components (null capability, fiber injection, achromatic phase shifter). Scientific capabilities of such a mission are presented. An exoplanet detection yield is derived, and we show that the detection of exoplanets around nearby stars is feasible. [less ▲]

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See detailExoplanet detection yield of a space-based Bracewell interferometer from small to medium satellites
Dandumont, Colin ULiege; Defrere, Denis ULiege; Kammerer, Jens et al

in Journal of Astronomical Telescopes, Instruments, and Systems (2020), 6(3),

Space-based nulling interferometry is one of the most promising solutions to spectrally characterize the atmosphere of rocky exoplanets in the mid-infrared (3 to 20  μm). It provides both high angular ... [more ▼]

Space-based nulling interferometry is one of the most promising solutions to spectrally characterize the atmosphere of rocky exoplanets in the mid-infrared (3 to 20  μm). It provides both high angular resolution and starlight mitigation. This observing capability depends on several technologies. A CubeSat (up to 20 kg) or a medium satellite (up to a few hundreds of kg), using a Bracewell architecture on a single spacecraft could be an adequate technological precursor to a larger, flagship mission. Beyond technical challenges, the scientific return of such a small-scale mission needs to be assessed. We explore the exoplanet science cases for various missions (several satellite configurations and sizes). Based on physical parameters (diameter and wavelength) and thanks to a state-of-the-art planet population synthesis tool, the performance and the possible exoplanet detection yield of these configurations are presented. Without considering platform stability constraints, a CubeSat (baseline of b  ≃  1  m and pupils diameter of D  ≃  0.1  m) could detect ≃7 Jovian exoplanets, a small satellite (b  ≃  5  m  /  D  ≃  0.25  m) ≃120 exoplanets, whereas a medium satellite (b  ≃  12.5  m  /  D  ≃  0.5  m) could detect ∼250 exoplanets including 51 rocky planets within 20 pc. To complete our study, an analysis of the platform stability constraints (tip/tilt and optical path difference) is performed. Exoplanet studies impose very stringent requirements on both tip/tilt and OPD control. [less ▲]

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See detailBenefits of photonic structuring on perovskite solar cells using opal-like layers
Lobet, Michaël ULiege; Mayer, Alexandre; Maho, Anthony ULiege et al

Poster (2020, August 26)

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See detailSolution uniqueness and noise impact in a static spectropolarimeter based on birefringent prisms for full Stokes parameter retrieval
Vasilescu, Bogdan ULiege; Loicq, Jerôme ULiege; Nazé, Yaël ULiege

in Journal of Astronomical Telescopes, Instruments, and Systems (2020), 6(2),

An innovative model of a static spectropolarimeter able to cover the entire Stokes vector is discussed. The optical layout is based on a birefringent modulator formed by two antiparallel prisms stuck ... [more ▼]

An innovative model of a static spectropolarimeter able to cover the entire Stokes vector is discussed. The optical layout is based on a birefringent modulator formed by two antiparallel prisms stuck together with the help of an intermediary part of the same material. This optical model has the advantage of being extremely compact. It avoids any movable parts or rotating components. By its architecture, the device induces a complete modulation on the vertical direction of any incoming polarized light, facilitating the determination of the entire Stokes vector through a single measurement. Because the modulation is also wavelength-dependent, spectral dependencies of the polarization states can be derived. The behavior of the model was first investigated in noise-free conditions. The existence of a unique solution was proven in the absence of noise and for any Stokes vector configuration. Under noisy conditions, the uncertainty on the Stokes parameters and the efficiency of the modulation scheme were evaluated as a function of the analyzer’s angle and for two different configurations of the modulator. The simulations show that an almost ideal efficiency is reachable, qualifying the concept for the high-precision measurement of the polarization. [less ▲]

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See detailStray light entrance pupil: an efficient tool for stray light characterization
Clermont, Lionel ULiege; Michel, Céline ULiege; Blain, Pascal ULiege et al

in Optical Engineering: the Journal of the Society of Photo-Optical Instrumentation Engineers (2020)

Stray light represents a major performance limitation for optical instruments. Analyses are done with ray-tracing software to evaluate the stray light performances of a design and, if necessary, improve ... [more ▼]

Stray light represents a major performance limitation for optical instruments. Analyses are done with ray-tracing software to evaluate the stray light performances of a design and, if necessary, improve it before manufacturing. Accurate simulations, however, require sending a sufficient number of rays. Hence, the process can be very time-consuming. We introduce the concept of stray light entrance pupil (SLEP) and demonstrate how it can be an efficient tool for simulating stray light for point sources. The SLEP defines a pupil over which light entering the optical system generates stray light reaching the detector. When that pupil is smaller than the first lens of the system, rays can be sent only through that pupil instead of the full lens aperture. Therefore, the time required to perform the simulation is reduced. Moreover, the efficiency can be further improved by defining a source with nonuniform ray density. The SLEP method is demonstrated on a wide-angle Earth observation camera and a time reduction up to about 20 is obtained. The SLEP concept can also be used to facilitate experimental characterization [less ▲]

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See detailOpal-Like Photonic Structuring of Perovskite Solar Cells Using a Genetic Algorithm Approach
Lobet, Michaël ULiege; Mayer, Alexandre; Maho, Anthony ULiege et al

in Applied Sciences (2020)

Light management is an important area of photovoltaic research, but little is known about it in perovskite solar cells. The present work numerically studies the positive effect of structuring the photo ... [more ▼]

Light management is an important area of photovoltaic research, but little is known about it in perovskite solar cells. The present work numerically studies the positive effect of structuring the photo-active layer of perovskite material. This structuration consists of a hybrid absorbing layer made of an uniform part and an opal-like part. A genetic algorithm approach allows us to determine the optimal combination among more than 1.4 􀵈 10􀬽 potential combinations. The optimal combination provides an internal quantum efficiency of 98.1%, nearly 2% higher than for an equivalent unstructured photo-active layer. The robustness of the optimum against potential experimental deviations, as well as the angular dependency of the proposed structure, are examined in the present study. [less ▲]

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See detailTechnological challenges for the Large Interferometer For Exoplanets (LIFE)
Defrere, Denis ULiege; Quanz, Sascha; Absil, Olivier ULiege et al

Scientific conference (2019, November 04)

LIFE is a project initiated in 2017 and officially kicked-off in 2019 to develop the science, technology and a roadmap for an ambitious space mission that will allow mankind for the first time to detect ... [more ▼]

LIFE is a project initiated in 2017 and officially kicked-off in 2019 to develop the science, technology and a roadmap for an ambitious space mission that will allow mankind for the first time to detect and characterize the atmospheres of dozens of warm, terrestrial extrasolar planets. Thanks to NASA's Kepler mission and dedicated, long-term exoplanet searches from the ground, we know that rocky exoplanets are ubiquitous in the Milky Way and very likely also in the immediate Solar neighbourhood. Detecting these nearest planets, understanding the (atmospheric) diversity of other worlds and searching for indications of habitability and biological activity is a cornerstone of 21st century astrophysics and will provide us a new perspective on our place in this Universe. After a brief introduction on the scientific objectives, we present in this talk the recent technology developments required for LIFE and present the main technological challenges to tackle before launching such a mission. [less ▲]

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See detailTRIUMF: Trifocal & EDOF
Gatinel, Damien; Pagnoulle, Christophe; Loicq, Jerôme ULiege

Conference (2019, September 13)

Developement of a new multifocal intra-occular lens chromatically corrected.

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See detailUsing a cubesat to improve irrigation: an innovative thermal imager
Laborde, Victor ULiege; Loicq, Jerôme ULiege; Habraken, Serge ULiege et al

Conference (2019, September 11)

Water management has become one of the most important issues since 70% of the fresh water available on Earth is used for irrigation. The growing food demand and the scarcity of water resources lead to the ... [more ▼]

Water management has become one of the most important issues since 70% of the fresh water available on Earth is used for irrigation. The growing food demand and the scarcity of water resources lead to the need to carefully monitor water use, considering agricultural fields of thousands of km². The intrinsic hydric stress of crops is an indicator of their water needs. Better water management and crops healthiness could be achieved if this stress could be measured quickly. Hydric stress can be retrieve by comparing the ground temperature (reference) and the leaf surface temperature (LST) which also depends on the transpiration ability of the plant. Yet, this measure is very unpractical without airborne/spaceborn sensors with good resolution. This finding has led to the birth of the OUFTI-NEXT mission. The recent advances in the field of nanosatellites and the rising attention they get from the space agencies have convinced the University of Liege to develop its own CubeSat mission to image the LST with thermal infrared light above extensive crops to provide data for irrigation schedule. The aim of the long term mission will be to fly a constellation of CubeSats to ensure daily coverage over various fields with resolution of 50m. In addition, hot singular events data can be retrieved such as forest fire, volcanoes activity, pollutant leaking, etc… Each CubeSat is a dual-band imager in both the middle wave infrared (MWIR) and the long wave infrared (LWIR). The scientific value of combining these bands is huge since LWIR gives accurate temperature measurements around 300K but with bad contrast, the latter being compensated by the MWIR which allows fine resolution. Each band is also sensitive to different atmosphere condition (humidity, clouds) and using both brings robustness to the mission. The current step of this ambitious project is to fly a single band 3U technology demonstrator to validate the use of MWIR technologies without space heritage and the scientific value of MWIR images for LST determination. This spectral band is very challenging, as it hardly allows diffraction-limited performances: it requires fast optics, more sensitive to aberrations. For this demonstrator, resolution of 100m without daily coverage is chosen, resulting from is a trade-off between science demonstration and mission size. The “new” infrared technologies include: high operating temperature detector, compact optics, passive athermalization and recent infrared materials. Solutions to make this challenging mission feasible are promising: The MWIR camera achieved diffraction-limited performances and uses compact hybrid lenses made of chalcogenide materials to reduce thermals effects and manufacturing costs. A very wide range of suitable detectors have been reviewed and the possibility to customize their integration is studied with their manufacturers. The orbit is sun-synchronous to optimize the thermal design and in accordance with both the radiometric budget and the observation strategy. [less ▲]

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See detailFeasibility study of an interferometric CubeSat for exoplanet science
Dandumont, Colin ULiege; Loicq, Jerôme ULiege; Defrere, Denis ULiege et al

Conference (2019, September 11)

Every week, new exoplanets are discovered mostly by the transit method (77.1% of all discoveries according to NASA). Even if this method is efficient at detecting planets, it is limited to a small ... [more ▼]

Every week, new exoplanets are discovered mostly by the transit method (77.1% of all discoveries according to NASA). Even if this method is efficient at detecting planets, it is limited to a small fraction of the whole expected exoplanets population due to the low probability of planetary transit. Therefore, a direct method is needed to detect and characterize exoplanets around the nearest stars. In this case, the planet and the star are angularly separated and photons are distinguished. It leads to the detection of the planet. Moreover, it allows the possible characterization of the planet surface or its atmosphere. One way to detect them through direct method is to use interferometry. With at least two sub-pupils (Bracewell interferometer), coherent light from the target is recombined to form interference patterns. The angular resolution depends on the baseline (distance between the two sub-pupils) and not on the diameter of each sub-pupil. Instead of using a single large telescope (around 60 cm diameter), which does not fit into a CubeSat, one can use two small and well separated apertures (around 10 cm each) to synthesize this large telescope. Therefore, it increases drastically the resolution power of CubeSats. In order to detect an exoplanet and get the direct light coming from it, the light from the star must be mitigated. It is called nulling interferometry. Thanks to a pi phase shift induced in one arm of the interferometer, destructive interferences are produced on the line-of-sight in order to suppress the light of the star. The exoplanet, which is on constructive interferences (white fringes), is unveiled. The Centre Spatial de Liège of the University is developing a space-based interferometer with a CubeSat. Goals are twofold: observe the nearest stars and demonstrate this technology in space, which will be a premiere. It is the first step towards a future large interferometry space-based mission which has the ambition to spectrally characterize Earth-like planets. The CubeSat will demonstrate light injection to optical fibers, recombination of the two beams, control of the delay-lines and detection. CubeSats offer low-cost demonstrator capabilities with a fixed baseline and with no free-flying concept. Aside the technical challenges, the second part of our researches is focused on the detection possibilities with this type of nanosatellite. We estimate by numerical simulations the possible science return for such an instrument. [less ▲]

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