Modal filtering is mandatory in nulling interferometers dedicated to direct detection of extrasolar terrestrial planets. However, up to date no appropriate waveguides to act as wavefront filter were available for the mid-infrared wavelengths in question. We present the development of silver-halide fibers and chalcogenide fibers to be used for modal filtering within the European DARWIN mission. We give a trade-off of suitable waveguides geometries, possible materials, and fabrication technologies and present measurements of the beam profiles, the insertion loss, and of the modal filtering capability of the developed fiber samples.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.