At the extreme contrast levels required to image Earth-like planets around Sun-like stars, the polarization dependence of the vector vortex coronagraph becomes a limiting factor, making wavefront control difficult to perform in both polarizations simultaneously. An alternative is to use a polarization-independent scalar vortex phase mask, but achromatizing scalar masks remains challenging. We investigate using metasurfaces to increase the bandwidth of scalar vortex phase masks. Our design shows an improvement of up to 2 orders of magnitude compared to a scalar vortex made of a helical-shaped dielectric substrate. However, the characteristic phase discontinuities of scalar vortex phase masks introduce phase artifacts and remain challenging to manufacture accurately. The cosine phase mask is an alternative approach to implementing a coronagraphic phase mask with a continuously varying azimuthal phase profile but without the phase jump of the scalar vortex. In addition, it requires smaller phase coverage. We therefore also investigate a metasurface implementation of the cosine mask. We present results obtained using rigorous coupled-wave analysis and finite-difference time-domain simulations and find that the phase jumps of a scalar vortex result in significant stellar leakage, which does not appear in the case of the cosine mask. We then present the simulated coronagraphic performance and residual chromaticity of both designs and discuss their advantages and drawbacks. We conclude that metasurface scalar vortex and cosine phase masks are promising coronagraphic phase masks in light of upcoming ground and space telescope missions combining deep contrast and insensitivity to low-order aberrations.
", "doi": "10.1117/1.jatis.11.2.025002", "issn": "2329-4124", "publisher": "SPIE-Intl Soc Optical Eng", "publication": "Journal of Astronomical Telescopes, Instruments, and Systems", "publication_date": "2025-04", "series_number": "02", "volume": "11", "issue": "02", "pages": "025002" }, { "id": "authors:1eex8-yrx24", "collection": "authors", "collection_id": "1eex8-yrx24", "cite_using_url": "https://authors.library.caltech.edu/records/1eex8-yrx24", "type": "article", "title": "Implicit electric field conjugation through a single-mode fiber", "author": [ { "family_name": "Liberman", "given_name": "Joshua", "orcid": "0000-0002-4934-3042", "clpid": "Liberman-Joshua" }, { "family_name": "Llop-Sayson", "given_name": "Jorge", "orcid": "0000-0002-3414-784X", "clpid": "Llop-Sayson-Jorge" }, { "family_name": "Bertrou-Cantou", "given_name": "Arielle", "clpid": "Bertrou-Cantou-Arielle" }, { "family_name": "Mawet", "given_name": "Dimitri", "orcid": "0000-0002-8895-4735", "clpid": "Mawet-D" }, { "family_name": "Desai", "given_name": "Niyati", "orcid": "0000-0002-2843-8325", "clpid": "Desai-Niyati" }, { "family_name": "Haffert", "given_name": "Sebastiaan Y.", "orcid": "0000-0001-5130-9153" }, { "family_name": "Eldorado Riggs", "given_name": "A. J.", "orcid": "0000-0002-0863-6228", "clpid": "Eldorado-Riggs-A-J" } ], "abstract": "Connecting a coronagraph instrument to a spectrograph via a single-mode optical fiber is a promising technique for characterizing the atmospheres of exoplanets with ground and space-based telescopes. However, due to the small separation and extreme flux ratio between planets and their host stars, instrument sensitivity will be limited by residual starlight leaking into the fiber. To minimize stellar leakage, we must control the electric field at the fiber input. Implicit electric field conjugation (iEFC) is a model-independent wavefront control (WFC) technique in contrast with classical EFC, which requires a detailed optical model of the system. We present here the concept of an iEFC-based WFC algorithm to improve stellar rejection through a single-mode fiber (SMF). As opposed to image-based iEFC, which relies on minimizing intensity in a dark hole region, our approach aims to minimize the amount of residual starlight coupling into an SMF. We present broadband simulation results demonstrating a normalized intensity ≥10\u207b¹\u2070 for both fiber-based EFC and iEFC. We find that both control algorithms exhibit similar performance for the low wavefront error (WFE) case, however, iEFC outperforms EFC by ≈100x in the high WFE regime. Having no need for an optical model, this fiber-based approach offers a promising alternative to EFC for ground and space-based telescope missions, particularly in the presence of residual WFE.
", "doi": "10.1117/1.jatis.10.2.029002", "issn": "2329-4124", "publisher": "SPIE-Intl Soc Optical Eng", "publication": "Journal of Astronomical Telescopes, Instruments, and Systems", "publication_date": "2024-05", "series_number": "02", "volume": "10", "issue": "02", "pages": "029002" } ]