TY - GEN
T1 - Vortex phase masks of topological charge 4 and higher with diamond subwavelength gratings
AU - König, Lorenzo
AU - Absil, Olivier
AU - Delacroix, Christian
AU - Lobet, Michaël
AU - Karlsson, Mikael
AU - Vargas Catalan, Ernesto
AU - Orban De Xivry, Gilles
AU - Loicq, Jerôme
AU - Habraken, Serge
N1 - Publisher Copyright:
© 2020 SPIE.
PY - 2020
Y1 - 2020
N2 - 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.
AB - 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.
KW - extrasolar planet
KW - high contrast imaging
KW - metasurfaces
KW - phase mask
KW - small inner working angle
KW - subwavelength grating
KW - vector vortex coronagraph
UR - http://www.scopus.com/inward/record.url?scp=85099783451&partnerID=8YFLogxK
U2 - 10.1117/12.2576166
DO - 10.1117/12.2576166
M3 - Conference contribution
AN - SCOPUS:85099783451
T3 - Proceedings of SPIE - The International Society for Optical Engineering
BT - Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV
A2 - Navarro, Ramon
A2 - Geyl, Roland
PB - SPIE
T2 - Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV 2020
Y2 - 14 December 2020 through 22 December 2020
ER -