We investigate the on-line writing identical fiber Bragg grating （FBG） arrays using the phase mask tech- nique. Given the limitation of laser power, the energy density uniformity and the horizontal width of the writing spot cannot be further optimized. The results show that the FBG arrays obtained in the optimal process （drawing speed of 12±0.15 m/min and average tension of 38.2 g） have a central wavelength bandwidth of less than 0.1 nm and an average refiectivity of 0.26%. Thus, the phase mask method is a promising alternative for on-line writing identical FBG arrays.
One method based on the end-face reflection as a reference was used to measure weak grating reflectivity of 0.01%-1%. For measuring ultra-weak grating reflectivity, the grating group with an identical wavelength was used. By using anhydrous alcohol and deionized water as the reflecting medium, the single- pulse FBG reflectivity of a highly doped-Ge photosensitive fiber was calculated to be about 0.747% and 0.739%, respectively; and the single-pulse FBG reflectivity of ordinary SMF fiber was about 0.016% and 0.015%, respectively. The consistent results by the two different reflecting media showed that the end-face reflection method on the grating group was feasible.
