Patent ID: 7679829
Filing Date: 2010-03-16
Classification: G02B

Abstract:
1. An apparatus for optically combining light beams, the apparatus providing for at least three beam paths that are partly combined into a null path and partly combined into fringe tracking paths for controlling nulling in the null path, the apparatus comprising: controllable phase shifters in respective ones of the beam paths; a series of beam combiners located in the beam paths after the controllable phase shifters, arranged to combine successively more of the beam paths into the null path; beam splitters for splitting the beam paths into the null path and fringe tracking paths, at least a first one of the beam splitters being located between a start and end of said series or being combined with one of the beam combiners in a splitter-combiner; fringe tracker sensors located in the fringe tracker paths each with an output to produce a fringe tracker signal; a control circuit with inputs coupled to the fringe tracker outputs and outputs coupled to the controllable phase shifters, and arranged to generate control signals for the controllable phase shifters from the fringe tracking signals to control nulling.