VISION: Next Generation Beam Combiner for the Navy Precision Optical Interferometer

The Visible Imaging System for Interferometric Observations at NPOI (VISION) is a versatile beam combiner for the Navy Precision Optical Interferometer (NPOI). VISION is a fiber-optics based beam combiner that can coherently combine light from up to 6 telescopes simultaneously using an image-plane combination scheme. VISION was inspired by the Michigan Infrared Combiner (MIRC) for the CHARA array - but VISION operates at optical wavelengths. With planned resolutions of <0.2 milli-arcseconds, VISION will be used to reconstruct multi-pixel time-varying images of evolved (luminosity class I-III) stars - in other words, movies of stellar surface variations. VISION’s visible light beam combination will be able to uniquely characterize surface features of stars less accessible at infrared wavelengths by interferometers such as CHARA. The “classic” beam combiner for NPOI employs a pupil-plane image combination which has visibility amplitude and closure phase precisions of 5-20% and 1-10 degrees respectively.VISION features a photometric camera for calibrations, spatial filtering from single mode fibers, and negligible read noise with a modern Andor Ixon CCD. These features will enable a factor of 10 improvement in visibility amplitude and closure phase precisions.