Implicit electric field conjugation for improved starlight rejection through a single-mode fiber

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 technique in contrast with classical electric field conjugation (EFC) which requires a detailed optical model of the system. We present here the concept of an iEFC-based wavefront control algorithm to improve stellar rejection through a single-mode fiber. 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 a single-mode fiber. We present broadband simulation results demonstrating a normalized intensity ≥ 10−10 for both fiber-based EFC and iEFC. We find that both control algorithms exhibit similar performance for the low wavefront error case, however, iEFC outperforms EFC by ≈ 100x in the high wavefront error regime. Having no need for an optical model, this fiber-based approach is theoretically easier to implement than conventional EFC on future ground and space-based telescope missions. © 2023 SPIE.