Single-mode octagonal photonic crystal fibers for the middle infrared

Single-mode optical fibers for the middle infrared are needed for many applications such as infrared fiber lasers, spatial filtering, and interferometry. Index guiding photonic crystal fibers offer many advantages over regular step-index fibers such as a wide spectral range and large core area. In this paper, we report the design and fabrication of single-mode octagonal photonic crystal fibers. These fibers were fabricated from silver halide polycrystalline materials which have high transmission in the middle infrared. The fibers showed a single-mode behavior at 10.6 μm with low losses and a large mode diameter (110 μm).