Vortex phase masks of topological charge 4 and higher with diamond subwavelength gratings

Lorenzo König; Olivier Absil; Christian Delacroix; Michaël Lobet; Mikael Karlsson; Ernesto Vargas Catalán; Gilles Orban de Xivry; Jérôme Loicq; Serge Habraken

doi:10.1117/12.2576166

13 December 2020 Vortex phase masks of topological charge 4 and higher with diamond subwavelength gratings

Lorenzo König, Olivier Absil, Christian Delacroix, Michaël Lobet, Mikael Karlsson, Ernesto Vargas Catalán, Gilles Orban de Xivry, Jérôme Loicq, Serge Habraken

Author Affiliations +

Proceedings Volume 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV; 1145144 (2020) https://doi.org/10.1117/12.2576166
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Conference Poster

Abstract

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.

Conference Presentation

Citation Download Citation

Lorenzo König, Olivier Absil, Christian Delacroix, Michaël Lobet, Mikael Karlsson, Ernesto Vargas Catalán, Gilles Orban de Xivry, Jérôme Loicq, and Serge Habraken "Vortex phase masks of topological charge 4 and higher with diamond subwavelength gratings", Proc. SPIE 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV, 1145144 (13 December 2020); https://doi.org/10.1117/12.2576166

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