Seeing the limited coupling of starlight into single‐mode fiber with a small telescope

Abstract

An optical fiber link to a telescope provides many advantages for spectrometers designed to detect and characterize extrasolar planets through precise radial velocity measurements. In the seeing‐limited regime, a multi‐mode fiber is typically used so that a significant amount of starlight may be captured. In the near‐diffraction‐limited case, either with an adaptive optics system or with a small telescope at an excellent site, efficiently coupling starlight into a much smaller, single‐mode fiber may be possible. In general, a spectrometer designed for single‐mode fiber input will be substantially less costly than one designed for multi‐mode fiber input. We describe the results of tests coupling starlight from a 70 cm telescope at Mt. Hopkins, Arizona into the single‐mode fiber of the MINERVA‐Red spectrometer at a wavelength of ∼$$ \sim $$850 nm using a low‐speed tip/tilt image stabilization system comprising all commercial, off‐the‐shelf components. We find that approximately 0.5%$$ \% $$ of the available starlight is coupled into the single‐mode fiber under seeing conditions typical for observatories hosting small telescopes, which is close to the theoretical expectation. We discuss scientific opportunities for small telescopes paired with inexpensive, high‐resolution spectrometers, as well as upgrade paths that should significantly increase the coupling efficiency for the MINERVA‐Red system.