Femtosecond point-by-point inscription of Bragg gratings by drawing a coated fiber through ferrule

A ferrule-based method of direct fs FBG inscription through protective plastic coating is demonstrated. Fluctuations of fiber core position relative to the writing fs beam are compensated by the developed auto-alignment system. As a result, high-quality FBGs with length from 0.1 to 50 mm are fabricated in polyimide-coated fibers, whose spectra are well described by the theory. The fabricated FBGs have great potential in sensor applications at high temperature and harsh environments both point-action and distributed ones.