First light of the FIRST visible fibered interferometer upgrade at the Subaru telescope

TL;DR

The paper reports on the first on-sky results of an upgraded fibered interferometer at Subaru, using integrated optics to enhance stability and sensitivity for high-contrast imaging and spectroscopy below the diffraction limit.

Contribution

It introduces the first on-sky demonstration of a visible-wavelength photonic chip beam combiner integrated into the FIRSTv2 interferometer at Subaru.

Findings

Successful on-sky testing of the photonic chip in FIRSTv2

Improved stability and sensitivity with integrated optics technology

Enhanced capability for detecting close companions like exoplanets

Abstract

FIRSTv2 (Fibered Imager foR a Single Telescope version 2) is the upgrade of a post-AO spectro-interferometer (FIRST) that enables high contrast imaging and spectroscopy at spatial scales below the diffraction limit of a single telescope. FIRST is currently installed, and routinely used, on the Subaru telescope as a module of the Subaru Extreme AO (SCExAO) platform. It achieves sensitivity and accuracy by a unique combination of sparse aperture masking, spatial filtering by single-mode fibers and cross-dispersion in the visible (600-900nm). The ongoing upgrade aims at using a photonic chip beam combiner, allowing the measurement of the complex visibility for every baseline independently. Using the integrated optics technology will increase the stability and sensitivity, and thus improve the dynamic range. Integrated optics chips working in the visible wavelength range are challenging (in terms of throughput and polarization). Several photonic chips are under characterization in our laboratory and we have installed a first prototype chip in the FIRSTv2 instrument at the Subaru Telescope. I will thus report on the on-sky results obtained with this kind of device, for the first time in the visible. This is the first step towards the full upgrade of FIRSTv2, that will ultimately provide unique capabilities to detect and characterize close companions such as exoplanets, by combining high angular resolution and spectral resolution in the visible.