FLUOR fibered instrument at the IOTA interferometer

Abstract

The FLUOR project started in 1991 with a prototype fiber recombination unit that transformed a pair of independent 80 cm telescopes into a stellar interferometer. An improved version of this unit is now used as part of the instrumentation at the IOTA interferometer on Mt Hopkins (Arizona). The system is based on fluoride glass single-mode waveguides (non polarization-preserving) for observations at infrared wavelengths between 2 and 2.4 μm. A triple coupler performs the coherent recombination of the beams and extracts two calibration signals. A passive polarization control is sufficient to maintain the interferornetric efficiency above 80 %, with variations of the order of a few percents from one night to the next. The combination FLUOR/JOTA now routinely provides stellar interferograms on baselines ranging between 5 and 38 m, with an accuracy of 1 % or better in the fringe visibility measurements.