Fiber Bragg gratings (FBGs) in cyclic transparent fluoropolymer (CYTOP) optical fiber are the subject of a lot of research as they can be of interest for many applications, such as temperature, humidity, strain, and radiation sensing. We report here a new technique to produce high quality FBGs in CYTOP fiber. It uses a femtosecond laser system operating at 400 nm and a phase mask. In contrast to previously reported results, the gratings are obtained in a few seconds with a writing power as low as 80 μW. With this setup, 2 mm-long gratings with reflectivity up to 92 % and full width at half maximum bandwidth around 0.5 nm were obtained in less than 10 s. The resonance wavelengths of the FBGs are confirmed by numerical computation in the graded-index multimode CYTOP fiber, and the mode selection characteristic of FBGs in CYTOP is investigated. Finally, the temperature sensitivity of CYTOP FBG is measured in different mode groups for heating up and cooling down, showing values independent of the mode group measured, but with a small hysteresis.

中文翻译：

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使用相位掩模和 400 nm 飞秒激光器在 CYTOP 聚合物光纤中刻录超快光纤布拉格光栅

环状透明含氟聚合物 (CYTOP) 光纤中的光纤布拉格光栅 (FBG) 是大量研究的主题，因为它们可用于许多应用，例如温度、湿度、应变和辐射传感。我们在这里报告了一种在 CYTOP 光纤中生产高质量 FBG 的新技术。它使用工作在 400 nm 的飞秒激光系统和相位掩模。与之前报道的结果相反，光栅是在几秒钟内获得的，写入功率低至 80 μW。通过这种设置，在不到 10 秒的时间内获得了反射率高达 92% 且半高带宽全宽约为 0.5 nm 的 2 mm 长光栅。在渐变折射率多模CYTOP光纤中通过数值计算确定了FBG的谐振波长，并研究了CYTOP中FBG的模式选择特性。