  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 greater than 10^{-10} 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 approximately 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.
