Analyse et correction des aberrations de bas ordre pour les coronographes à masque de phase

The direct detection of young and warm extrasolar giant planets in the habitable zone of nearby cool stars is one of the major goals of current ground-based high contrast imaging (HCI) instruments. To characterize such exoplanets by spectroscopy of their atmospheres requires isolating the planet light from the brighter stellar light, which is challenging due to high contrast at small angular separation. Using high performance small inner working angle (IWA) coronagraphs, it is possible to detect faint companions in the proximity of the stellar source. However, the uncontrolled pointing errors and other low-order wavefront aberrations degrade the rejection capability of these coronagraphs by leaking starlight around the coronagraphic focal plane mask. This additional unwanted light can prevent detection of a companion at small angular separation. How well these wavefront aberrations upstream of various coronagraphs can be controlled and calibrated is the focus of my thesis.To prevent coronagraphic leaks at small IWA, I worked on a concept where within a coronagraph, the low-order wavefront aberrations are sensed at the Lyot plane. The starlight diffracted by the focal plane mask is reflected by the Lyot stop towards a detector, which reliably estimates low-order aberrations present in the wavefront. I called this new sensor a Lyot-based low-order wavefront sensor (LLOWFS). During the course of my thesis, I have designed, developed and programmed this sensor and implemented it on the Subaru Coronagraphic Extreme Adaptive Optics instrument at the Subaru Telescope. In this thesis, I present the principle of the LLOWFS and the very first simulation with a Four Quadrant Phase Mask (FQPM) coronagraph. I study the sensitivity of the Phase-Induced Amplitude Apodization (PIAA) coronagraph, the Vector Vortex Coronagraph (VVC), the FQPM and the Eight Octant Phase Mask coronagraphs to low-order wavefront aberrations. I present the measurement of low-order errors up to 35 Zernike modes for all the coronagraphs and using a 2000-actuator Deformable Mirror, I demonstrate a closed-loop pointing accuracy between 10^-3 l/D and 10^-4 l/D in H-band in the laboratory. On-sky, I demonstrate the low-order control of 10 Zernike modes for the PIAA and the VVC and demonstrated a closed-loop accuracy of 10^-4 l/D under good seeing and 10^-3 l/D under moderate seeing on a routine basis.I present in this thesis the versatility of this new coronagraphic wavefront sensor by demonstrating its compatibility with different coronagraphs. Due to its simplicity in the design, the existing/planned ground-based HCI instruments can easily implement LLOWFS and control the low-order aberrations beyond pointing errors near the IWA of their coronagraphs. The next generation of space coronagraphs with a dedicated LLOWFS-like technology can also address the telescope pointing errors caused by the reaction wheels and thermal variations.La détection directe de jeunes et chaudes planètes extrasolaires géantes dans la zone habitablede naines rouges est l’un des principaux objectifs des instruments d’imagerie à hautcontraste pour les télescopes au sol actuels. Pour caractériser l’atmosphère de ces exoplanètespar spectroscopie, il est nécessaire d’isoler la lumière planétaire de celle de sonétoile, ce qui est difficile en raison du contraste élevé entre leurs luminosités ainsi queleur faible séparation angulaire. En utilisant un coronographe de haute performance pouvantobserver très près de l’étoile, il est possible de détecter des compagnons de faibleintensité près de la source stellaire. Cependant, les erreurs de pointage non contrôléesainsi que les autres aberrations de bas ordre dégradent le contraste de ces coronographescausant des fuites stellaires autour du masque coronographique. Cette lumière indésirablepeut empêcher la détection d’un compagnon à faible séparation angulaire. L’étalonnageet le contrôle de ces aberrations de front d’onde en amont de divers coronographes estl’objet de ma thèse.Pour éviter les fuites stellaires à faible séparation angulaire, j’ai travaillé sur un conceptoù les aberrations de bas ordre sont détectées au niveau du plan de Lyot du coronographe.La lumière stellaire, diffractée par le masque en plan focal, est réfléchie par le masque deLyot vers un détecteur, qui mesure précisément ces aberrations. J’ai appelé ce nouveausenseur un senseur d’aberrations de bas ordre dans le plan de Lyot (Lyot-based Low-OrderWavefront sensor ou LLOWFS en anglais). Au cours de ma thèse, j’ai mis en placeet programmé ce senseur sur l’instrument d’optique adaptative extrême du télescope Subaru.Dans cette thèse, je présente le principe du LLOWFS et une première simulation avecun coronographe â quatre quadrants. J’ai ensuite étudié la sensibilité de différents coronographesaux aberrations de bas ordre : le Phase Induced Amplitude Apodization (PIAA)coronagraph, le Vector Vortex coronagraph (VVC), ainsi que les coronographes à quatrequadrants et à huit octants. Je présente la mesure des bas ordres en laboratoire jusqu’à35 modes de Zernike pour ces coronographes, et l’aide d’un miroir dèformable muni de2000 actionneurs, je démontre un résidu de pointage en boucle fermée entre 10^-3 l/D et10^-4 l/D en bande H. Sur ciel derrière le télescope, je démontre la mesure de 10 modes deZernike pour le coronographe PIAA et le VVC, ainsi qu’un résidu de pointage en bouclefermée de 10-4 l/D dans de bonnes conditions de visibilité, et de 10-3 l/D lorsque les conditionssont dégradées. Enfin, je présente dans cette thèse la polyvalence de ce nouveausenseur de front d’onde en démontrant sa compatibilité avec différents coronographes.En raison de sa simplicité dans sa mise en oeuvre, les instruments à haut contraste existantsainsi que leurs successeurs peuvent facilement utiliser le LLOWFS pour mesurer etcontrôller les aberrations de bas ordre au plus près de l’étoile. La prochaine génération decoronographes spatiaux peuvent également utiliser cette technologie pour contrôler les erreursde pointage causées par la vibration des roues à réaction ainsi que par les variationsthermiques du télescope

Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications

The rapid proliferation of the Internet has been driving communication networks closer and closer to their limits, while available bandwidth is disappearing due to an ever-increasing network load. Over the past decade, optical fiber communication technology has increased per fiber data rate from 10 Tb/s to exceeding 10 Pb/s. The major explosion came after the maturity of coherent detection and advanced digital signal processing (DSP). DSP has played a critical role in accommodating channel impairments mitigation, enabling advanced modulation formats for spectral efficiency transmission and realizing flexible bandwidth. This book aims to explore novel, advanced DSP techniques to enable multi-Tb/s/channel optical transmission to address pressing bandwidth and power-efficiency demands. It provides state-of-the-art advances and future perspectives of DSP as well

The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report

The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument

The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report

The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument.Comment: Full report: 498 pages. Executive Summary: 14 pages. More information about HabEx can be found here: https://www.jpl.nasa.gov/habex