SPICA-FT: The new fringe tracker of the CHARA array

TL;DR

SPICA-FT is a new fringe tracking system integrated into the CHARA array, combining an innovative optics chip and software for improved interferometric measurements, with successful laboratory and initial on-sky testing results.

Contribution

This paper introduces the design, implementation, and testing of SPICA-FT, a novel integrated optics fringe tracker for the CHARA array, including its software architecture and on-sky performance evaluation.

Findings

Laboratory characterization of the integrated optics chip and software.

Initial on-sky tests conducted in 2020 and 2022.

Preliminary performance metrics of SPICA-FT system.

Abstract

SPICA-FT is part of the CHARA/SPICA instrument which combines a visible 6T fibered instrument (SPICAVIS) with a H-band 6T fringe sensor. SPICA-FT is a pairwise ABCD integrated optics combiner. The chip is installed in the MIRC-X instrument. The MIRC-X spectrograph could be fed either by the classical 6T fibered combiner or by the SPICA-FT integrated optics combiner. SPICA-FT also integrates a dedicated fringe tracking software, called the opd-controller communicating with the main delay line through a dedicated channel. We present the design of the integrated optics chip, its implementation in MIRC-X and the software architecture of the group-delay and phase-delay control loops. The final integrated optics chip and the software have been fully characterized in the laboratory. First on-sky tests of the integrated optics combiner began in 2020. We continue the on-sky tests of the whole system (combiner + software) in Spring and Summer 2022. We present the main results, and we deduce the preliminary performance of SPICA-FT.