飞秒激光烧蚀长周期光纤光栅的高温特性研究

Research on high- temperature characteristics of LPFGs fabricated by femtosecond laser ablation

为了探索包层去除型长周期光纤光栅的高温传感特性,利用中心波长为800 nm,脉冲宽度为120 fs的飞秒激光烧蚀直写而成并对其进行高温传感检测。首先,通过两块轴线互相垂直的柱透镜将入射激光聚焦成细长焦线,并借助垂直方向CCD成像系统精确定位光纤与焦点的相对位置;然后,通过激光器内嵌shutter与运动平台的耦合控制,实现光纤光栅的精确去除加工;最后,将写制的光纤光栅置于800℃的高温炉中放置2 h。利用高温管式电热炉对所加工光纤光栅在30～1100℃内进行温度传感测试,发现其在30～300℃内谐振波长的温度灵敏度为51 pm/℃,线性度为0.956;但在高温段300～1100℃内,其温度灵敏度达到了135pm/℃,线性度高达0.999。实验结果表明,这种通过包层表面定量去除的长周期光纤光栅更适用于高温及超高温环境的传感检测。

In order to explore the high- temperature characteristics of long period fiber gratings（ LPFG） whose cladding is partly removed,a laser operating at 800 nm with 120 fs duration pulse is used to ablate and fabricate a LPFG,and its high- temperature sensing characteristics are detected. Firstly,emission laser beam is focused to a slender focal line by two cylindrical lens whose axises are mutually perpendicular. The relative position between the fiber and the focus can accurately be decided with the aid of CCD observation placed in the vertical direction. Then LPFG can be accurately removed through the coupling control of the shutter embedded in the laser and the position platform.Lastly,the LPFG is placed in the furnace with a steady temperature of 800 ℃ for two hours. Its high- temperature sensitivity characteristics are tested in the high temperature tube furnace. The sensitivity of 51 pm /℃ and a linearity of 0. 956 within the temperature range of 30 ～ 300 ℃ is achieved,while the sensitivity reaches to 135 pm /℃ and the linearity is 0. 999 within the temperature range of 300 ～ 1100 ℃. The experimental results show that such LPFG whose cladding is partly removed is more suitable for sensor detection in high- temperature or super high- temperature surroundings.