Final Design and On-Sky Testing of the iLocater SX Acquisition Camera: Broadband Single-Mode Fiber Coupling

TL;DR

This paper details the design, construction, and successful on-sky testing of a broadband single-mode fiber injection system for the iLocater spectrograph on the LBT, demonstrating high coupling efficiency and advancing ground-based fiber-fed astronomical instruments.

Contribution

It presents the first on-sky demonstration of broadband single-mode fiber coupling for an astronomical spectrograph, showcasing a significant milestone in instrument development.

Findings

Achieved over 35% fiber coupling efficiency in the near-infrared

Successfully demonstrated on-sky performance across various conditions

Validated the instrument's design and operational capabilities

Abstract

Enabling efficient injection of light into single-mode fibers (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fiber injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broadband single-mode fiber coupling in excess of 35% (absolute) in the near-infrared (0.97-1.31{\mu}m) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality.