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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。
A focused and infrared femtosecond laser type I fiber Bragg grating (FBG) typed by UV laser was used to conduct single point and scanning exposure experiments respectively. Emphasis was placed on the impulse energy of the femtosecond laser pulse far below the damage threshold of the fiber. Effect of Laser on Grating Spectrum. The experimental results show that when the laser is irradiated at any position in the gate region, the spectrum of the laser is red-shifted and the spectral structure is no longer a single transmission peak but an irregular multi-transmission peak. However, the Bragg wavelength after the irradiation is blue-shifted And the transmittance of the grating increases. As the exposure time increases, the change gradually becomes saturated. By establishing a non-uniform temperature field diffusion model, the laser-induced refractive index changes will be superimposed on the refractive index modulation distribution of the original grating. The theoretical simulation of the spectral changes after different exposure time and exposure process is in good agreement with the experimental results.