Field of view of fiber interferometers and applications to OHANA

The use of single-mode optical fibers in interferometers allows both easy transport of the telescope beams and very accurate visibility measurements, thanks to their spatial filtering property. Unfortunately, spatial filtering reduces the field of view coupled in the interferometer to approximately the size of the diffraction limit of the largest telescope in the array. More seriously, the time-variable wavefront aberrations induced by the atmosphere continuously change the coupling properties of the fibers, and consequently, what each arm of the interferometer "sees" on the sky. These field of view effects are especially important for the next generation of interferometers, such as OHANA (Optical Hawaiian Array for Nanoradian Astronomy), where adaptive optics makes it possible to use large individual telescopes, and the increased sensitivity makes possible the observation of fainter, more extended objects with complex morphology. In this paper, the impact of these effects is studied for observations of a variety of sources by OHANA. It is shown that the errors in visibility measurements can be reduced by signal processing techniques. Possible solutions to extend the accessible field of view of fiber-based interferometers are also presented.