Fully symmetric nulling beam combiners

A simple method of nulling broadband Light is presented. A mirror-symmetric pair of right-angle periscopes is first used to introduce a geometric fiel d flip between two incident light beams, after which the light is combined by means of one of a number of constructive two-beam interferometers. A rec iprocal pair of beam-splitter passages provides for complete symmetry. Such an approach greatly eases beam-splitter design requirements and should fin d use both in initial ground-based nulling experiments and ultimately in sp ace-borne interferometers targeted at direct extrasolar planet detection.