Suppression of the Thermal Effects in the Femtosecond Laser Processing of Fiber Bragg Gratings

The thermal effects on the processing of type-I IR fiber Bragg gratings (FBGs) using a femtosecond laser with a phase mask are investigated. Thermal effects are significantly suppressed by using interval exposure mode and reducing the tension on the fiber. FBGs with improved photo-induced refractive index modulation are fabricated in the standard telecom fiber. The index modulation reaches 1.6×10^?3. The reflectivity and bandwidth are measured to be ?0.36 dB and 1.27 nm, respectively.