Deep Nulling by Means of Multiple-Beam Recombination

Direct detection of exoplanets is possible by use of a technique called nulling interferometry, which is based on destructive interference of light of the bright object and constructive interference of the faint object. In the infrared wavelength region, this implies that light of a star must be attenuated by a certain factor, the so-called rejection ratio, which typically equals 10^6 . This can be achieved by use of phase shifters, which apply a phase shift of (pi) rad with an average error no greater than 2 mrad over a predefined wavelength region. For a 6 -18- (mu)m wavelength interval, this is a tough constraint. We show that the 2-mrad constraint can be relaxed if more than two beams participate in the beam recombination. We focus our attention on dispersive phase shifters and show that rejection ratios beyond 10^6 can be reached easily by use of a system of four or more apertures and simple dispersive phase shifters that consist of only one materia