Square-lattice large-pitch hollow-core photonic crystal fiber.

We report on the design, fabrication and characterization of silica square-lattice hollow core photonic crystal fibers optimized for low loss guidance over an extended frequency range in the mid-IR region of the optical spectrum. The fiber's linear optical properties include an ultra-low group velocity dispersion and a polarization cross-coupling as low as -13.4 dB over 10 m of fiber.