Design of a 'self-nulling' beam combiner needing no external phase inversion

The complex optics of planned space-based nulling interferometers intended to search for exosolar planets will be simplified substantially if the modified Mach-Zehnder beam combiner is used in a novel fashion, extracting the null from ports traditionally used as bright outputs. This approach entirely eliminates the need for special phase-flipping optics, exploiting instead the broad-band phase shifts intrinsic to the beam splitters themselves. The theory of this 'self-nulling' approach is presented, and specifications are given for its use with and without adaptive nulling.