High flexibility inscription of FBG via femtosecond laser

Point by point (PbP) method via femtosecond (fs) laser is considered as a highly flexible way for inscribing FBGs, which is demonstrated in different core with various central wavelengths previously. In this letter, the flexible inscription has been further expanded to regulate reflectivity, 3 dB bandwidth, and sidelobe suppression. The influence law has been discovered for the first time that there is a trade-off among the laser energy, the transverse offsets and the grating order for pursuing smaller 3 dB bandwidth and higher sidelobe suppression on high reflectivity FBGs. The results show that increasing the grating order is a more efficient way. Quasi distributed FBGs are inscribed on a continuous fiber for further confirming its flexibility.