Fiber bragg gratings fabricated by femtosecond laser micromachining methods

High quality FBGs have been fabricated in our lab using three types of femtosecond laser inscription techniques, i.e. Phase Mask method, Line-by-Line method and Point-by-Point method. It is found that Phase Mask method shows the best spectral quality and repeatability but the flexibility is poor; Line-by-Line method exhibits good flexibility where nearly all the grating parameters can be adjusted but the writing efficiency is low; Point-by-Point method owns the best inscription efficiency but the cladding mode resonance is hard to avoid.