New method to achieve the proper polarization state for a vector vortex coronagraph

Characterizing the atmospheres of Earth-sized planets necessitates of the advancement in broadband wavefront control for coronagraph systems in large segmented telescopes. At the the High-Contrast Spectroscopy Testbed (HCST) in the Exoplanet Technology Laboratory (ET Lab) at Caltech we are working on a new concept that utilizes single mode fibers (SMFs) at the image plane of the coronagraph to recover the light from the planet and feed it into a spectrograph. This technology has shown to be advantageous in both chromatic and wavefront control performance. Here we report on the status of our 20% bandwidth wavefront control experiments, in which we control the starlight coupling into an SMF in the image plane. We achieve levels of 10⁻⁸ with deformable mirror (DM) solutions that hold the null through the SMF for several hours.