Silver halide single-mode fibers for the middle infrared

There is an interest in single-mode fibers that are highly transparent in the middle infrared. Such fibers would be valuable for spectroscopy, interferometry, fiber lasers, and heterodyne detection. We developed core-clad fibers made of crystalline silver halides, with external diameter 900 μm, small core diameters (50-60 μm) and an extremely small difference (∼0.004) between the indices of refraction of the core and the clad. These fibers behaved as single-mode fibers at the wavelength 10.6 μm.