Silver halide single mode fibers for broadband middle infrared stellar interferometry

We report the demonstration of silver halide single mode fibers at λ=7.5 ^μm. The fiber's modal behavior was tested at λ=10.6 and λ=7.5 ^μm, using near field measurements. Single mode operation was observed for both wavelengths with propagation losses of ∼16 and ∼40 dB/m at λ=10.6 and λ=7.5 ^μm, respectively. A rejection ratio of ∼30 dB was achieved at λ=7.5 ^μm for a 30 cm long fiber segment. These fibers would be particularly useful for modal filtering in the 6-20 ^μm band. Modal filters are essential technology elements in nulling stellar interferometry.