Interferometric Coupling of the Keck Telescopes with Single-Mode Fibers

Abstract

Here we report successful interferometric coupling of two large telescopes with single-mode fibers. Interference fringes were obtained in the 2- to 2.3-micrometer wavelength range on the star 107 Herculis by using the two Keck 10-meter telescopes, each feeding their common interferometric focus with 300 meters of single-mode fibers. This experiment demonstrates the potential of fibers for future kilometric arrays of telescopes and is the first step toward the 'OHANA (Optical Hawaiian Array for Nanoradian Astronomy) interferometer at the Mauna Kea observatory in Hawaii. It opens the way to sensitive optical imagers with resolutions below 1 milli-arc second. Our experimental setup can be directly extended to large telescopes separated by many hundreds of meters.

Phase closure nulling

“…Phase closure nulling experiments on dwarf stars with HJs would only be possible today on a handful of them since the baseline needed to null a Sun equivalent at 10 pc is ≈1000 m at 1.65 μm. This restriction can be overcome in the near future as fibered interferometers with kilometer baselines are currently underway (Perrin et al 2006).…”

Telescope arrays give fine view of stars

“…Guy Perrin, an astronomer at the Paris Observatory and principal investigator for the Optical Hawaiian Array for Nano-radian Astronomy (OHANA), is connecting the seven large telescopes at the summit into an array with a baseline of 800 metres. As a proof of principle, Perrin has already combined light from the two Keck telescopes via inconspicuous optical fibres, which would obviate the need to connect the telescopes with tunnels 3 . Reached by telephone atop the summit, Perrin last week was busy implementing a second stage -a fibre-optic link to connect the Gemini North telescope to the CanadaFrance-Hawaii Telescope.…”

Astronomical photonics in the context of infrared interferometry and high-resolution spectroscopy

“…They also permit in principle to transport beams over a long distance from the telescope focus down to an optical back-end. Experiments such as the OHANA project have attempted to bypass complex optical trains of the Keck interferometer using long (∼300 m) single-mode fiber cables directly plugged at each telescopes focus 73 . Multimode fibers in fiber-fed spectrographs efficiently enable multiplexed observations of few hundreds objects per pointing.…”