  FIRST, the Fibered Imager foR a Single Telescope instrument, is an ultra-high
angular resolution spectro-imager, able to deliver calibrated images and
measurements beyond the telescope diffraction limit, a regime that is out of
reach for conventional AO imaging. FIRST achieves sensitivity and accuracy by
coupling the full telescope to an array of single mode fibers. Interferometric
fringes are spectrally dispersed and imaged on an EMCCD. An 18-Fiber FIRST
setup is currently installed on the Subaru Coronographic Extreme Adaptive
Optics instrument at Subaru telescope. It is being exploited for binary star
system study. In the late 2020 it will be upgraded with delay lines and an
active LiNb03 photonic beam-combining chip allowing phase modulation to
nanometer accuracy at MHz. On-sky results at Subaru Telescope have demonstrated
that, thanks to the ExAO system stabilizing the visible light wavefront, FIRST
can acquire long exposure and operate on significantly fainter sources than
previously possible. A similar approach on a larger telescope would therefore
offer unique scientific opportunities for galactic (stellar physics, close
companions) and extragalactic observations at ultra-high angular resolution. We
also discuss potential design variations for nulling and high contrast imaging.
