Annealing of the Induced Birefringence by UV and IR Lasers in Fiber Bragg Gratings

The annealing curves of the birefringence induced by both ultraviolet (UV) and femtosecond infrared (fs-IR) lasers in fiber Bragg gratings (FBGs) are examined. Experimental results show that the induced birefringence in hydrogen (H₂)-loaded SMF-28 fibers by both UV and IR lasers can be annealed completely at low temperatures when moderate FBGs are inscribed (index modulation less than 10^-3). For strong gratings inscribed by UV laser in H₂-loaded SMF-28 fiber and gratings inscribed by fs-IR laser in unloaded SMF-28 fiber, the birefringence annealing curves strongly depend on the laser wavelength, laser power and the exposure time.