  Exoplanet direct imaging using adaptive optics (AO) is often limited by
non-common path aberrations (NCPAs) and aberrations that are invisible to
traditional pupil-plane wavefront sensors (WFSs). This can be remedied by
focal-plane (FP) WFSs that characterize aberrations directly from a final
science image. Photonic lanterns (PLs) can act as low-order FPWFSs with the
ability to direct some light to downstream science instruments. Using a PL on
the SEAL (Santa Cruz Extreme AO Laboratory) high-contrast imaging testbed, we
demonstrate (1) linear ranges and (2) closed-loop control. Additionally, we
simulate the use of the PL in a multi-wavefront sensor AO system, in which
multiple WFSs feed back to the same common-path deformable mirror. Building on
previous multi-WFS AO demonstrations on SEAL, we simulate a modulated pyramid
WFS to sense aberrations of high spatial order and large amplitude, and the PL
to sense low order aberrations including NCPAs. We assess adaptive optics
performance in this setting using three different PL wavefront reconstruction
algorithms. We also provide a new method to experimentally identify the
propagation matrix of a PL, making advanced model-based algorithms practical.
This work demonstrates the role of photonic technologies and multi-stage
wavefront sensing in the context of extreme AO and high contrast imaging.
