High-precision fringe tracking invariant to systematic model errors

We present a new approach to processing of interferometric data, which dramatically improves operation on the smallest fraction of the fringe (∼1/1000 of a wavelength and beyond). In particular, this approach, dubbed the variation-in variant subspace tracking approach (VISTA), makes it possible to operate a Michelson interferometer in a highly stable mode in which the estimation of optical path delay becomes invariant (insensitive) to a large class of systematic model errors. This previously unknown invariance property of interferometry follows from the fundamental odd-even symmetry of the channeled spectrum and its derivatives. VISTA offers a powerful algorithmic alternative for alleviating technological challenges in the design of high-precision long-baseline spaceborne interferometers. © 2001 Optical Society of America.