Fabrication of Bragg Gratings in Random Air-Line Clad Microstructured Optical Fiber

Fiber Bragg gratings (FBGs) are written using an infrared (IR) femtosecond laser and a phase mask into pure silica microstructured optical fiber having a cladding region comprised of random air-lines (RAL). Scanning electron microscopy measurements of the IR irradiated RAL fiber samples shows the presence of subwavelength nanograting structures associated with thermally stable type II Bragg gratings. High temperature annealing testing shows that although the RAL FBGs have a high degree of stability even at 1000 °C, they are less stable than similar FBGs made in single mode telecom fiber (SMF-28).