This Small Business Innovation Research Phase I project will demonstrate the feasibility of applying advanced nonlinear fringe tracking algorithms to enable astronomers to track dimmer stars. Ground based stellar optical interferometers are limited in the amount of sky coverage achievable by the lack of stars bright enough to serve as guide stars. This problem cannot be solved by Adaptive Optics (AO) means alone. The fringe tracking subsystem has been identified as the performance limiting subsystem for optical interferometric arrays. State-of-the-art data processing algorithms utilized for fringe tracking functions use linear correlation filters and make limited use of atmospheric turbulence information. This situation presents an opportunity for advanced fringe tracking algorithms that make use of all the available statistical information and can naturally handle the measurement nonlinearities. The proposed algorithms have the additional advantage of being complementary to AO systems. The goal of the Phase I effort is to establish the possibility of coherent tracking with reduced signal-to-noise requirements through the use of advanced algorithms, and thus to enable the observation of dimmer (by about one bolometric magnitude) target stars. The resulting software product would be invaluable for current and planned interferometric arrays world-wide, both military and scientific. This technology would also be of use to optics manufacturing houses with a need for interferometric metrology testing of precision surfaces for large optical components.
