This Letter reports a novel helical sapphire fiber Bragg grating (HSFBG) in a single crystal sapphire fiber with diameter of 60 µm fabricated by a 515 nm femtosecond laser. Due to the large refractive index modulation region and high structural symmetry of the HSFBGs, high-reflectivity and high-quality spectra can be prepared and additionally have good bending resistance. The spectral properties of HSFBGs with different helical diameters are studied. When the helical diameter is 30 µm, the reflectivity of HSFBG is 40%, the full width at half-maximum is 1.56 nm, and the signal-to-noise ratio is 16 dB. For the HSFBG bending test, the minimum bending radius is 5 mm, which can still maintain relatively good spectral quality. In addition, the HSFBG array with different periods has been successfully cascaded in a sapphire fiber. The experimental results of the HSFBG high-temperature test show that this HSFBG can work reliably at 1600°C, and the temperature sensitivity in the high-temperature range can reach 35.55 pm/°C. This HSFBG can be used in high-temperature and harsh environments, such as metal smelting and aeroengine structural health monitoring.

中文翻译：

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飞秒激光刻制螺旋蓝宝石光纤布拉格光栅

这封信报告了由 515 nm 飞秒激光器制造的直径为 60 µm 的单晶蓝宝石光纤中的新型螺旋蓝宝石光纤布拉格光栅 (HSFBG)。由于HSFBGs的大折射率调制区域和高结构对称性，可以制备高反射率和高质量的光谱，并且还具有良好的抗弯曲性。研究了具有不同螺旋直径的 HSFBG 的光谱特性。当螺旋直径为30 µm时，HSFBG的反射率为40%，半高宽为1.56 nm，信噪比为16 dB。对于HSFBG弯曲测试，最小弯曲半径为5mm，仍能保持较好的光谱质量。此外，不同周期的HSFBG阵列已成功级联在蓝宝石光纤中。HSFBG高温测试的实验结果表明，该HSFBG可在1600°C下可靠工作，高温范围内的温度灵敏度可达35.55 pm/°C。该HSFBG可用于金属冶炼、航空发动机结构健康监测等高温恶劣环境。