Core-scanned fibre Bragg gratings inscribed using ultrashort pulses and a point by point setup

Fibre Bragg gratings (FBGs) are key components in fibre laser development, and femtosecond laser inscription has paved the way for highly stable and robust monolithic fibre laser systems [1]. There are two fundamental approaches for femtosecond laser inscription of FBGs: phase mask scanning [2] and the point-by-point (PbP) [3] technique. The phase mask technique offers high period stability and reproducibility but limited flexibility over the grating period. The PbP technique offers complete flexibility in the grating period; in fact local phase shifts and continuous chirp have been demonstrated [4]. However these gratings exhibit significant scattering loss [5]. Zhou et al. [6] proposed a new writing technique where 4^th order gratings where inscribed line by line; however these still show high scattering losses. We present a core-scanning technique for FBGs using a PbP inscription setup that benefits from the flexibility over the grating period, but has drastically reduced scattering losses.