Development of infrared single mode fibers for 2 wavelength bands of the DARWIN mission: Test results of prototypes

Various space telescope array systems are being considered to investigate other terrestrial planets orbiting around nearby stars in order to find extra-terrestrial life. One of them is the DARWIN mission of the European Space Agency (ESA). The required technology is the nulling interferometer. The challenge of nulling is making the null in the interferometric signal sufficiently deep to cancel the light from the bright star during the collection of light from its surrounding planets. The performance of the nulling is limited by the wavefront quality of the beams. The wavefront error can be reduced by filtering using a single mode fiber. For the DARWIN mission, the operational wavelength range is 6.5-20μm. Within the current ESA project, this is covered by a dual-band fiber system. A chalcogenide glass fiber based on the Te-As-Se (TAS) composition is selected to be used for the short wavelength band. For the long wavelength band up to 20 μm, Tellurium based glass is proposed. Different samples of various composition based on Te glass are manufactured and tested. The fibers are designed by TNO and different prototypes have been manufactured by the University of Rennes. Test setups are developed to demonstrate/investigate the single mode operation. Cladding modes are found to disturb the single mode operation. The effect of cladding modes is modeled. Solutions to eliminate the cladding modes are investigated and tested. © 2009 SPIE.