Disentanglement of mixed interference fringes in optical interferometers: theory and applications

Optical interferometric imaging enables astronomical observation at extremely high angular resolution. The necessary optical information for imaging, such as the optical path differences and visibilities, is easy to extract from fringes generated by the combination of two beams. With more than two apertures, the image-plane interference pattern becomes an increasingly indistinguishable mixture of fringe spacings and directions. For decades, the state-of-the-art approaches for obtaining two-aperture fringes from an interferometer array composed of many apertures are limited to pairwise combinations using bulk optics. Here, we derive and demonstrate a fringe disentanglement theory that can digitally transform the interference pattern of N apertures to N(N-1)/2 pairwise fringes without any optics, thus providing straightforward methods of information acquisition for interferometers. We demonstrate applications of our technique by both simulation and experiment, showing that this theory can be used for simultaneously sensing pistons and determining the individual visibilities of all combining apertures. Furthermore, we use the proposed theory to phase a 1.5-meter segmented flat telescope, demonstrating its validity for engineering implementation. This theory may not only benefit optical imaging but also interferometry-based measurements, by providing an exceptional capability to simplify the interferometric output generated by a system of many apertures.