Miniature beam combiners for optical and NIR interferometers.

One of the critical components of a separated element interferometer is the beam combiner. The initial alignment of the separate optical elements that make up this device and the maintenance of that alignment is usually problematical, Fibre optic devices provide an answer to the alignment difficulties but in single mode form have a restricted bandwidth. This paper discusses the design of a number of devices to overcome these short comings. These beam combiners can he small in size, their dimensions largely governed by the beam diameter. Large diameter beams are only necessary to reduce diffraction effects on the journey from the telescope to the beam combiner. On arrival the beam diameter can then be reduced to suit the beam combiner. Small, stable and low weight beam combiners are an advantage on the ground but even more so in space applications. Designs for combining the beams for large numbers of telescope are described.