Thermally Stable Type II FBGs Written Through Polyimide Coatings of Silica-Based Optical Fiber

Abstract

Type II-IR fiber Bragg gratings (FBGs) were written directly through the protective polyimide coatings of off-the-shelf pure silica core and standard telecom Ge-doped silica core single mode fibers using ultrafast IR radiation and the phase mask FBG writing method. Using a short focal length acylindrical lens and nonlinear photoluminescent imaging, type II grating structures could be created when Fourier transform limited pulses were chirped to 500 fs. The resulting gratings in the Ge-doped fibers were thermally stable up to 1000 °C and could be used directly as fabricated without annealing to stabilize the structure.