High precision differential astrometry assesses the positions, distances, and motions of celestial objects in relation to the stars. The focal plane of such space telescope must be calibrated with a precision down to the level of 1e-5 pixel in order to be able to detect Earth-like planets in the close vicinity of the Sun. The presented characterization bench is designed to improve the technology readiness level for the following key points: calibration of new detectors with a high number of pixels and correcting the field distortion using stars in the field of view. The first aim of the project concentrates on the characterization of a 46 megapixels sensor from PYXALIS, to assess its typical parameters using an integrating sphere. The next objective intends to map the intra and extra pixel quantum yield of the detector with a precision of 1e-5 pixels and investigate the evolution of the pixel geometry in response to environment fluctuations. To conduct these tests, an optical bench is designed with an LCD screen and a doublet, used as a source that allows directing light to specific groups of pixels. Interferometric calibration of the detector pixel centroid position will be achieved using fibers that illuminate the detector with Young's fringes. To characterize the distortion of the detector, a diaphragm will produce adjustable optical aberrations to be corrected and therefore change the source sensor positional relationship. The final step involves the simulation of a star's field, which will be imaged on the detector to assess optical quality.

High precision differential Astrometry is the branch of astronomy that evaluates the relative position, distance and motion of celestial objects with respect to the stars present in the field of view. A mission called Theia has been submitted in 2022 for ESA's M7 call for missions, using a diffraction-limited telescope about 1m in diameter and with a field of view of 0.5 degrees, capable of achieving sub-micro-arcsecond angular accuracy, corresponding to 1e-5 pixel on the detector. Such precision makes it possible to study the nature of dark matter in our galaxy and to reveal the architecture of exoplanetary systems close to the Sun, down to the mass of the Earth. The aim of the experimental tests presented in this poster is to improve the TRL of 2 specific aspects: the calibration of new CMOS detectors with very large number of pixels and the calibration of the telescope aberrations.First, a key element of such a space telescope is the focal plane, which must be calibrated spatially with an extreme precision down to the 1e-5 pixel level. Previous work has shown that this is possible with small detector matrices (80x80 px) [1]. The goal is now to check the performances and validate this method with the new very large detectors. Pyxalis, a company based near Grenoble, is developing very large detectors (8000x5000 px) that have a low noise level and high sensitivity. The aim is to characterize and validate this type of detectors in a laboratory demonstration (see poster Pancher et al.), to ensure that the performance achieved meets the required specifications. We present the results of these characterization in this contribution.The telescope stability is also a sensitive issue. Recent work [2] has shown that the reference stars in the field of the telescope can be used as actual metrology sources in order to compute the field distortion function. Our simulations allow to model the optical aberrations with bivariate polynoms. The effects on the calibration accuracy of the degrees of the polynoms, the number of reference stars and the tilt perturbation of the M2 mirror are investigated. This poster will present the latest results obtained on a test bed developed to experimentally study the performances of this new field calibration method.

La première démonstration mondiale du potentiel de l’optique adaptative pour l’astronomie a été effectuée en 1989. Ces travaux ont démontré qu’il était possible de compenser les effets de la turbulence atmosphérique et d’atteindre la limite de diffraction des grands télescopes, au moins dans le proche infrarouge. Couplée éventuellement à l’utilisation d’étoiles artificielles créées par laser, cette technologie est devenue une composante incontournable de tous les grands télescopes optiques terrestres. Les observations ayant conduit au Prix Nobel de Physique 2020 ont reposé sur les premiers développements de l’imagerie des tavelures, puis rapidement sur ceux de l’optique adaptative et de son application à l’interférométrie multi-télescopes.

This paper, “Integrated optics applied to astronomical aperture synthesis III: simulation of components optimized for astronomical interferometry," was presented as part of International Conference on Space Optics—ICSO 1997, held in Toulouse, France.

This paper, “Integrated optics applied to astronomical aperture synthesis: general concept for space and ground based applications," was presented as part of International Conference on Space Optics—ICSO 1997, held in Toulouse, France.

912191JS'rl , , ,,, )a5,1(Ift'.jN',f,n'LJ P MI 17 3u,t({_1R/lU,7 t4C1f

Integrated optics, applied to astronomical interferometry, bring several decisive benefits compared to bulk optics : mechanical and thermal stability, small size, facility to realize combiners for many telescopes. At this time, numerous compoments were dezigned, realized and tested for stellar interferometry applications. Laboratory characterization in the VIS/NIR wavelengths confirm the expected capabilities and performances. At thermal infrared wavelengths, the concept of integrated optics is of great interest for spatial instrumentations and particulary for the Darwin/IRSI mission. The aim of the mission, launched in 2012−2015, is the detection and the spectroscopic study of extrasolar planets. Our long term goal is the development of monomode integrated optic components for thermal infrared wavelengths. In the near futur, we are interested by the conception and the realization of single mode straight waveguide for using in modal filtering. In this paper, we present the conception of first thermal waveguide and their characterizations. Around different solutions, we focused our attention on the utilization of chalcogenide glasses because of its wide transmission window, from 1 to 20 microns depending of the material composition, and of the potentially low propagation losses.

We report in this paper decisive advance on the detector development for the astronomical applications that require very fast operation. Since the CCD220 and OCAM2 major success, new detector developments started in Europe either for visible and IR wavelengths.Funded by ESO and the FP7 Opticon European network, the NGSD CMOS device is fully dedicated to Natural and Laser Guide Star AO for the E-ELT with strong ESO involvement. The NGSD will be a 880x840 pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate and providing digital outputs. A camera development, based on this CMOS device and also funded by the Opticon European network, is ongoing.Another major AO wavefront sensing detector development concerns IR detectors based on Avalanche Photodiode (e-APD) arrays within the RAPID project. Developed by the SOFRADIR and CEA/LETI manufacturers, the latter offers a 320x255 8 outputs 30 microns IR array, sensitive from 0.4 to 3 microns, with less than 2 e readout noise at 1600 fps. A rectangular window can also be programmed to speed up even more the frame rate when the full frame readout is not required. The high QE response, in the range of 70%, is almost flat over this wavelength range. Advanced packaging with miniature cryostat using pulse tube cryocoolers was developed in the frame of this programme in order to allow use on this detector in any type of environment. The characterization results of this device are presented here. Readout noise as low as 1.7 e at 1600 fps has been measured with a 3 microns wavelength cut-off chip and a multiplication gain of 14 obtained with a limited photodiode polarization of 8V. This device also exhibits excellent linearity, lower than 1%. The pulse tube cooling allows smart and easy cooling down to 55 K. Vibrations investigations using centroiding and FFT measurements were performed proving that the miniature pulse tube does not induce measurable vibrations to the optical bench, allowing use of this cooled device without liquid nitrogen in very demanding environmental conditions. A successful test of this device was performed on sky on the PIONIER 4 telescopes beam combiner on the VLTi at ESO-Paranal in June 2014.First Light Imaging, which will commercialize a camera system using also APD infrared arrays in its proprietary wavefront sensor camera platform.These programs are held with several partners, among them are the French astronomical laboratories (LAM, OHP, IPAG), the detector manufacturers (e2v technologies, Sofradir, CEA/LETI) and other partners (ESO, ONERA, IAC, GTC, First Light Imaging). Funding is: Opticon FP7 from European Commission, ESO, CNRS and Universite de Provence, Sofradir, ONERA, CEA/LETI the French FUI (DGCIS), the FOCUS Labex and OSEO.

NEAT (Nearby Earth Astrometric Telescope) is an astrometric space mission aiming at detecting Earth-like exoplanets located in the habitable zone of nearby solar-type stars. For that purpose, NEAT should be able to measure stellar centroids within an accuracy of 5 10(-6) pixels. In order to fulfil such stringent requirement, NEAT incorporates an interferometric metrology system measuring pixel gains and location errors. To validate this technology and assess the whole performance of the instrument, a dedicated test bench has been built at IPAG, in Grenoble (France). In this paper are summarized the main system engineering considerations allowing to define sub-systems specifications. Then we describe the general architecture of the performance models (including photometric, interferometric, and final astrometric budgets) and confront their predictions with the experimental results obtained on the test bench. It is concluded that most of error items are well understood, although some of them deserve further investigations.

We report the fabrication of single-mode buried channel waveguides for the whole mid-IR transparency range of chalcogenide sulphide glasses (λ ≤ 11 μm), by means of direct laser writing. We have explored the potential of this technology by fabricating a prototype three-dimensional three-beam combiner for future application in stellar interferometry that delivers a monochromatic interference visibility of 99.89% at 10.6 μm and an ultrahigh bandwidth (3-11 μm) interference visibility of 21.3%. These results demonstrate that it is possible to harness the whole transparency range offered by chalcogenide glasses on a single on-chip instrument by means of direct laser writing, a finding that may be of key significance in future technologies such as astrophotonics and biochemical sensing.

The purpose of this paper is to give an overview of the state of the art wavefront sensor detectors developments held in Europe for the last decade. The success of the next generation of instruments for 8 to 40-m class telescopes will depend on the ability of Adaptive Optics (AO) systems to provide excellent image quality and stability. This will be achieved by increasing the sampling, wavelength range and correction quality of the wave front error in both spatial and time domains. The modern generation of AO wavefront sensor detectors development started in the late nineties with the CCD50 detector fabricated by e2v technologies under ESO contract for the ESO NACO AO system. With a 128x128 pixels format, this 8 outputs CCD offered a 500 Hz frame rate with a readout noise of 7e-. A major breakthrough has been achieved with the recent development by e2v technologies of the CCD220. This 240x240 pixels 8 outputs EMCCD (CCD with internal multiplication) has been jointly funded by ESO and Europe under the FP6 programme. The CCD220 and the OCAM2 camera that operates the detector are now the most sensitive system in the world for advanced adaptive optics systems, offering less than 0.2 e readout noise at a frame rate of 1500 Hz with negligible dark current. Extremely easy to operate, OCAM2 only needs a 24 V power supply and a modest water cooling circuit. This system, commercialized by First Light Imaging, is extensively described in this paper. An upgrade of OCAM2 is foreseen to boost its frame rate to 2 kHz, opening the window of XAO wavefront sensing for the ELT using 4 synchronized cameras and pyramid wavefront sensing. Since this major success, new developments started in Europe. One is fully dedicated to Natural and Laser Guide Star AO for the E-ELT with ESO involvement. The spot elongation from a LGS Shack Hartman wavefront sensor necessitates an increase of the pixel format. Two detectors are currently developed by e2v. The NGSD will be a 880x840 pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate. The LGSD is a scaling of the NGSD with 1760x1680 pixels and 3 e readout noise (goal 1e) at 700 Hz (goal 1000 Hz) frame rate. New technologies will be developed for that purpose: advanced CMOS pixel architecture, CMOS back thinned and back illuminated device for very high QE, full digital outputs with signal digital conversion on chip. In addition, the CMOS technology is extremely robust in a telescope environment. Both detectors will be used on the European ELT but also interest potentially all giant telescopes under development. Additional developments also started for wavefront sensing in the infrared based on a new technological breakthrough using ultra low noise Avalanche Photodiode (APD) arrays within the RAPID project. Developed by the SOFRADIR and CEA/LETI manufacturers, the latter will offer a 320x240 8 outputs 30 microns IR array, sensitive from 0.4 to 3.2 microns, with 2 e readout noise at 1500 Hz frame rate. The high QE response is almost flat over this wavelength range. Advanced packaging with miniature cryostat using liquid nitrogen free pulse tube cryocoolers is currently developed for this programme in order to allow use on this detector in any type of environment. First results of this project are detailed here. These programs are held with several partners, among them are the French astronomical laboratories (LAM, OHP, IPAG), the detector manufacturers (e2v technologies, Sofradir, CEA/LETI) and other partners (ESO, ONERA, IAC, GTC). Funding is: Opticon FP6 and FP7 from European Commission, ESO, CNRS and Université de Provence, Sofradir, ONERA, CEA/LETI and the French FUI (DGCIS).

NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. In NEAT, one fundamental aspect is the capability to measure stellar centroids at the precision of 5e-6 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 4e-5 pixel at Nyquist sampling. Simulations showed that a precision of 2 micro-pixels can be reached, if intra and inter pixel quantum efficiency variations are calibrated and corrected for by a metrology system. The European part of the NEAT consortium is designing and building a testbed in vacuum in order to achieve 5e-6 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. In this paper we give the basic relations and trade-offs that come into play for the design of a centroid testbed and its metrology system. We detail the different conditions necessary to reach the targeted precision, present the characteristics of our current design and describe the present status of the demonstration.

Light gathered and focused by a telescope must often be refocused onto spectrographs and other complex instruments. To such ends, astronomers are coming to realize the benefits of photonics.

In an optical interferometer, the phase of astronomical signals is corrupted not only by the Earth's atmosphere, but also by instrumental artifacts, among which birefringence, that affects the relative phase of two orthogonal polarizations. Instrumental birefringence occurs at each mirror reflection, but can also occur in the instrument where the signals are recombined., especially when optical fibers are used on the signal path. We present here a new technique to cancel instrumental birefringence, in the context of the PIONIER instrument at the VLTI (ESO, Paranal observatory). This is achieved by introducing in each of the beams a birefringent plate with an adjustable inclination, that allows to cancel the differential birefringence between the beams before recombination. We present our derivation of the amount of birefringence introduced by such an inclined plate. We show the actual performance achieved with the Pionier instrument. The initial alignment takes of order of one hour, and is stable for several days. Tweaking is performed at the beginning of each observing run and takes approximately fifteen minutes. We demonstrate a simple and effective technique to cancel differential birefringence in interferometric instruments. This technique should be applicable to second generation VLTI instruments.

We present here our recent progress in the three-dimensional (3D) direct laser writing (DLW) of step-index core waveguides inside diverse technologically relevant dielectric substrates, with specific emphasis on the demonstration of DLW mid-infrared waveguiding in the whole transparency range of these materials.

This article reports the advances on the development of mid-infrared integrated optics for stellar interferometry. The devices are fabricated by laser writing techniques on chalcogenide glasses. Laboratory characterizaton is reported and analyzed.

Depuis la fin des années 90, les astronomes utilisent l’interférométrie de manière régulière comme outil d’observation pour dépasser la limite de résolution des plus grands télescopes actuels. Après une période de validation au moyen de premiers prototypes de réseaux de télescopes, l’effort est porté maintenant sur l’optimisation de l’instrumentation utilisée au foyer des réseaux opérationnels. Des progrès technologiques sont attendus, en particulier en matière de détection, pour étendre le domaine d’application de cette technique très puissante.

Context. A new four-telescope interferometric instrument called PIONIER has recently been installed at VLTI. It provides improved imaging capabilities together with high precision. Aims. We search for low-mass companions around a few bright stars using different strategies, and determine the dynamic range currently reachable with PIONIER. Methods. Our method is based on the closure phase, which is the most robust interferometric quantity when searching for faint companions. We computed the chi^2 goodness of fit for a series of binary star models at different positions and with various flux ratios. The resulting chi^2 cube was used to identify the best-fit binary model and evaluate its significance, or to determine upper limits on the companion flux in case of non detections. Results. No companion is found around Fomalhaut, tau Cet and Regulus. The median upper limits at 3 sigma on the companion flux ratio are respectively of 2.3e-3 (in 4 h), 3.5e-3 (in 3 h) and 5.4e-3 (in 1.5 h) on the search region extending from 5 to 100 mas. Our observations confirm that the previously detected near-infrared excess emissions around Fomalhaut and tau Cet are not related to a low-mass companion, and instead come from an extended source such as an exozodiacal disk. In the case of del Aqr, in 30 min of observation, we obtain the first direct detection of a previously known companion, at an angular distance of about 40 mas and with a flux ratio of 2.05e-2 ±0.16e-2. Due to the limited u,v plane coverage, its position can, however, not be unambiguously determined. Conclusions. After only a few months of operation, PIONIER has already achieved one of the best dynamic ranges world-wide for multi-aperture interferometers. A dynamic range up to about 1:500 is demonstrated, but significant improvements are still required to reach the ultimate goal of directly detecting hot giant extrasolar planets.

We compare the filtering capabilities of two infrared fibers developed to achieve a high rejection ratio of the higher order modes in order to obtain compact modal filters devoted to stellar interferometry. Two types of double-clad fibers are studied: a fiber with a second thin absorbing cladding and a fiber with a second thick absorbing cladding closer to the fiber core; both are single mode around the CO2 band (10.6 μm). We present the single-mode spectral domain and the nulling capabilities of both fibers for different fiber lengths, comparing simulations with experimental results. We show that the filtering capabilities are improved when the absorbing clad is closer to the fiber core, as the propagation distance needed to filter out these modes is shorter. Thus, to obtain high rejection ratios in compact devices, an absorbing cladding close to the core of the fiber is compulsory in order to suppress cladding modes that could eventually recouple into the waveguide. We present an empirical model that allows determining the minimum filter length, considering only one effective leaky mode with low attenuation, which considerably simplifies the theoretical studies.