  One of the biggest challenges associated with a nulling interferometer-based
approach to detecting extra-solar Earth-like planets comes from the extremely
stringent requirements of pathlength, polarization and amplitude matching in
the interferometer. To the extent that the light from multiple apertures are
not matched in these properties, light will leak through the nuller and confuse
the search for a planetary signal. Here we explore the possibility of using the
coherence properties of the starlight to separate contributions from the planet
and nuller leakage. We find that straightforward modifications to the optical
layout of a nulling interferometer will allow one to measure and correct for
the leakage to a high degree of precision. This nulling calibration relaxes the
field matching requirements substantially, and should consequently simplify the
instrument design.
