Opt Lett. 2018 Aug 15;43(16):3893-3896. doi: 10.1364/OL.43.003893.
Two slightly shifted gratings are inscribed, one over the other, while exploiting fiber strain in a single-mode fiber. The inscription is done with a near-infrared femtosecond laser, a phase mask, and a cylindrical focusing lens. The first fiber Bragg grating (FBG) is inscribed under normal fiber tension, while the second overlapping FBG is inscribed under higher fiber tension. The transmission spectrum of the complex structure is similar to that of a phase-shifted grating, yet the fabrication process is much faster and simpler compared to other standard methods. A high-quality phase-shifted grating with two -30 dB transmission dips, a 25 dB transmission peak, and <50 pm transmission bandwidth is achieved. We observe polarization-dependent transmission in the phase-shifted gratings.
两个略微错开的光栅被刻写在同一根单模光纤上，利用光纤应变实现。刻写过程使用近红外飞秒激光、相位掩模和圆柱聚焦透镜完成。第一个光纤布拉格光栅（FBG）在正常光纤张力下刻写，而第二个重叠 FBG 在更高的光纤张力下刻写。该复杂结构的传输光谱类似于相移光栅，但与其他标准方法相比，其制造过程更快、更简单。实现了具有两个 -30 dB 传输衰减、25 dB 传输峰值和 <50 pm 传输带宽的高质量相移光栅。我们观察到相移光栅中的偏振相关传输。
