Department of Electromagnetism and Telecommunication, Faculty of Engineering, University of Mons, Boulevard Dolez 31, Mons B-7000, Belgium.
Opt Lett. 2013 Feb 15;38(4):594-6. doi: 10.1364/OL.38.000594.
We report highly birefringent fiber Bragg gratings in standard single-mode optical fiber realized with UV femtosecond pulses and line-by-line inscription. By controlling the three-dimensional positioning of the focused laser beam with respect to the fiber core, we achieve very high birefringence at the grating location in a single exposure. A maximum birefringence value of 7.93×10(-4) has been reached for 10th-order gratings when using 2 μJ pulses, which is to our knowledge the highest birefringence value reported so far. This birefringence results from UV-induced high-densification lines shifted from the center of the core, increasing the asymmetry of the induced-stress lines. With a Bragg wavelength spacing reaching more than 800 pm between polarization modes, such gratings are particularly well suited for selective filtering or, as demonstrated here, for temperature-insensitive transverse-strain measurements.
我们报告了在标准单模光纤中用紫外飞秒脉冲和逐线写入技术实现的高度双折射光纤布拉格光栅。通过控制聚焦激光束相对于光纤芯的三维位置，我们在单次曝光中就在光栅位置实现了非常高的双折射。当使用 2 μJ 脉冲时，第 10 阶光栅的最大双折射值达到了 7.93×10(-4)，就我们所知，这是迄今为止报道的最高双折射值。这种双折射是由从芯中心偏移的紫外光诱导的高密度线引起的，增加了诱导应力线的不对称性。这种光栅的布拉格波长间隔超过 800 pm，在偏振模式之间，因此特别适合选择性滤波，或者，如这里所示，用于温度不敏感的横向应变测量。
