采用聚焦的红外飞秒激光对紫外激光刻写的Ⅰ型光纤布拉格光栅(FBG)分别进行了单点和扫描式曝光实验，重点研究了飞秒激光脉冲能量远低于光纤的损伤阈值情况下，脉冲激光对光栅光谱的影响。实验发现，激光单点照射栅区任意位置时，照射过程中的光谱有较大红移，且光谱结构不再是单透射峰而是不规则的多透射峰；然而照射结束后的布拉格波长蓝移且光栅透射率增加，随着曝光时间的增加该变化逐渐趋于饱和。通过建立非均匀温度场扩散模型，激光诱导的折射率变化会叠加在原光栅的折射率调制分布上，理论仿真了不同曝光时间后和曝光过程中的光谱变化，与实验结果非常吻合。

Single point and scan exposure experiments on ultraviolet laser inscribed type I fiber Bragg grating by focused infrared femtosecond laser are reported. The effect of femtosecond laser pulses on the grating transmission spectrum is studied especially when the pulse energy density is far lower than the fiber damage threshold. Experimental results show that the grating spectrum during irradiation shows a red shift, and the spectral structure is no longer a single transmission peak but more irregular transmission peaks. However, after stopping exposure, the resonant wavelength shows blue shift phenomemon and the transmissivity increases, which tend to be saturated with the time increasing. The grating exposure region is considered to be in a non-uniform temperature field, and the laser-induced refractive index change overlaps the original grating refractive index modulation distribution. The spectrum change during exposure and after a certain time ′s exposure is theoretically simulated and the simulation results fit well with the experimental ones.