Characterization of Single-Mode Fiber Coupling at the Large Binocular Telescope

Abstract

Optimizing on-sky single-mode fiber (SMF) injection is an essential part of developing precise Doppler spectrometers and new astrophotonics technologies. We installed and tested a prototype SMF injection system at the Large Binocular Telescope (LBT) in April 2016. The fiber injection unit was built as part of the de-risking process for a new instrument named iLocater that will use adaptive optics (AO) to feed a high resolution, near-infrared spectrograph. In this paper we report Y-band SMF coupling measurements for bright, M-type stars. We compare theoretical expectations for delivered Strehl ratio and SMF coupling to experimental results, and evaluate fundamental effects that limit injection efficiency. We find the pupil geometry of the telescope itself limits fiber coupling to a maximum efficiency of rho_tel=0.78. Further analysis shows the individual impact of AO correction, tip-tilt residuals, and static (non-common-path) aberrations contribute coupling coefficients of rho_Strehl=0.33, rho_tip/tilt=0.84, and rho_ncpa=0.8 respectively. Combined, these effects resulted in an average Y-band SMF efficiency of 0.18 for all observations. Finally, we investigate the impact of fiber coupling on radial velocity (RV) precision as a function of stellar apparent magnitude.

References in corpus (6)

• Efficient injection from large telescopes into single-mode fibres: Enabling the era of ultra-precision astronomy
• Insights on the Spectral Signatures of Stellar Activity and Planets from PCA
• Improving Planet-Finding Spectrometers
• Enhancing stellar spectroscopy with extreme adaptive optics and photonics
• iLocater: A Diffraction-limited Doppler Spectrometer for the Large Binocular Telescope
• On-sky single-mode fiber coupling measurements at the Large Binocular Telescope

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• Solar photospheric spectrum microvariability II. Observed relations to magnetic activity and radial-velocity modulation
• 3D-M3: High-spatial resolution spectroscopy with extreme AO and 3D printed micro-lenslets
• On-sky results for the novel integrated micro-lens ring tip-tilt sensor