Single-Mode Index-Guiding Photonic Crystal Fibers for the Middle Infrared

Single-mode optical fibers for the middle infrared (mid-IR) (m) are needed for many applications such as IR fiber lasers, spatial filtering, and interferometry. There has only been limited success in the development of such fibers, due to the lack of suitable materials that have high transmission in this spectral range. In this letter, we discuss the development and optical measurements on single-mode index-guiding photonic crystal fibers based on silver-halide crystalline materials which are highly transparent in the mid-IR. These fibers were designed to have a large core area and to maintain a single-mode operation over a wide spectral range.