On-sky single-mode fiber coupling measurements at the Large Binocular Telescope

TL;DR

This paper reports on on-sky measurements of single-mode fiber coupling efficiency at the Large Binocular Telescope, demonstrating the system's performance under various observing conditions to inform future instrument design.

Contribution

It provides the first on-sky characterization of SMF coupling at LBT using AO, including performance analysis across different conditions for the development of the iLocater spectrograph.

Findings

SMF coupling efficiency varies with telescope elevation.

The system performs reliably under different seeing conditions.

Installation and alignment procedures are detailed for future replication.

Abstract

The demonstration of efficient single-mode fiber (SMF) coupling is a key requirement for the development of a compact, ultra-precise radial velocity (RV) spectrograph. iLocater is a next generation instrument for the Large Binocular Telescope (LBT) that uses adaptive optics (AO) to inject starlight into a SMF. In preparation for commissioning iLocater, a prototype SMF injection system was installed and tested at the LBT in the Y-band (0.970-1.065 $\mu$m). This system was designed to verify the capability of the LBT AO system as well as characterize on-sky SMF coupling efficiencies. SMF coupling was measured on stars with variable airmasses, apparent magnitudes, and seeing conditions for six half-nights using the Large Binocular Telescope Interferometer. We present the overall optical and mechanical performance of the SMF injection system, including details of the installation and alignment procedure. A particular emphasis is placed on analyzing the instrument's performance as a function of telescope elevation to inform the final design of the fiber injection system for iLocater.