  FIRST (Fibered Imager foR a Single Telescope instrument) is a post-AO
instrument that enables high contrast imaging and spectroscopy at spatial
scales below the diffraction limit. FIRST achieves sensitivity and accuracy by
a unique combination of sparse aperture masking, spatial filtering by
single-mode fibers and cross-dispersion in the visible. The telescope pupil is
divided into sub-pupils by an array of microlenses, coupling the light into
single-mode fibers. The output of the fibers are rearranged in a non redundant
configuration, allowing the measurement of the complex visibility for every
baseline over the 600-900 nm spectral range. A first version of this instrument
is currently integrated to the Subaru Extreme AO bench (SCExAO). This paper
focuses on the on-going instrument upgrades and testings, which aim at
increasing the instrument's stability and sensitivity, thus improving the
dynamic range. FIRSTv2's interferometric scheme is based on a photonic chip
beam combiner. We report on the laboratory characterization of two different
types of 5-input beam combiner with enhanced throughput. The interferometric
recombination of each pair of sub-pupils is encoded on a single output. Thus,
to sample the fringes we implemented a temporal phase modulation by pistoning
the segmented mirrors of a Micro-ElectroMechanical System (MEMS). By coupling
high angular resolution and spectral resolution in the visible, FIRST offers
unique capabilities in the context of the detection and spectral
characterization of close companions, especially on 30m-class telescopes.

Instrumentation and Methods for Astrophysics