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Vortex phase masks of topological charge 4 and higher with diamond subwavelength gratings
König, Lorenzo; Absil, Olivier; Delacroix, Christian et al.
2020In Navarro, R; Geyl, R (Eds.) Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV
 

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Keywords :
extrasolar planet; high-contrast imaging; small inner working angle; vector vortex coronagraph; subwavelength grating; phase mask; metasurfaces
Abstract :
[en] 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.
Research Center/Unit :
STAR - Space sciences, Technologies and Astrophysics Research - ULiège
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
König, Lorenzo ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > PSILab
Absil, Olivier  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > PSILab
Delacroix, Christian  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > PSILab
Lobet, Michaël;  Ctr. Spatial de Liège, Univ. de Liège (Belgium)
Karlsson, Mikael;  Uppsala Univ. (Sweden)
Vargas Catalán, Ernesto;  Uppsala Univ. (Sweden)
Orban De Xivry, Gilles  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > PSILab
Loicq, Jerôme  ;  Université de Liège - ULiège > CSL (Centre Spatial de Liège)
Habraken, Serge  ;  Université de Liège - ULiège > Département de physique > Optique - Hololab
Language :
English
Title :
Vortex phase masks of topological charge 4 and higher with diamond subwavelength gratings
Publication date :
13 December 2020
Event name :
SPIE Astronomical Telescopes + Instrumentation 2020
Event organizer :
SPIE
Event date :
14 - 18 Dec 2020
Audience :
International
Main work title :
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV
Author, co-author :
Navarro, R
Geyl, R
Publisher :
SPIE
Collection name :
Proc SPIE 11451
Pages :
1145144
European Projects :
H2020 - 819155 - EPIC - Earth-like Planet Imaging with Cognitive computing
Name of the research project :
EPIC
Funders :
EC - European Commission
Available on ORBi :
since 29 April 2021

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