基于狭缝整形的低损耗飞秒光纤光栅制备

Fabrication of low loss femtosecond fiber Bragg gratings based on slit shaping

为了解决飞秒激光逐点法制备的光纤布拉格光栅(Fiber Bragg Gratings,FBG)损耗较高的问题,利用逐面法完成飞秒光纤光栅制备的实验研究。运用高斯光束传播的基本理论,通过狭缝整形技术对聚焦的飞秒激光能量分布进行等高宽整形,突破在光纤横截面内诱导产生圆形折射率调制的难点,最终制备得到低损耗的飞秒光纤光栅。开展不同狭缝宽度制备FBG的光谱特性对比实验,结果表明:利用光斑直径为5.0 mm的飞秒激光光束刻写FBG时,采用宽度为1.7 mm的狭缝制备得到的FBG插入损耗降低至0.15 dB,短波损耗降低至0.5 dB,验证了基于狭缝整形的低损耗飞秒光纤光栅制备方法的有效性。针对狭缝法制备的FBG反射率分散问题,提出控制折射率匹配液填充量以及调整飞秒激光能量的方法,并优化光束聚焦流程,成功降低FBG反射率的分散度。本研究对推动飞秒光纤光栅在大容量、高链路损耗等环境中的实际应用具有重要意义。

In order to solve the problem of high loss of fiber Bragg gratings(FBGs)fabricated by femtosecond laser point by point,experimental research on the fabrication of femtosecond fiber Bragg gratings was completed using the plane⁃by⁃plane method.Using the basic theory of Gaussian beam propagation,the focused femtosecond laser energy distribution was contoured with equal height and width using slit shaping technology,breaking through the difficulty of inducing circular refractive index modulation within the fiber cross⁃section,and ultimately fabricating low loss femtosecond fiber gratings.Comparative experiments were conducted on the spectral characteristics of FBG fabricated with different slit widths.The results showed that when using a femtosecond laser beam with a spot diameter of 5.0 mm to write FBG,the insertion loss of the FBG prepared with a slit width of 1.7 mm was reduced to 0.15 dB,and the short⁃wavelength loss was reduced to 0.5 dB.This verified the effectiveness of the low loss femtosecond fiber grating fabrication method based on slit shaping.A method is proposed to control the filling amount of refractive index matching solution and adjust the femtosecond laser energy for the problem of dispersion of FBG reflectivity fabricated by the slit method,and the beam focusing process is optimized to successfully reduce the dispersion of FBG reflectivity.This study is of great significance in promoting the practical application of femtosecond fiber gratings in environments with high capacity and high chain loss.