在高速飞行器、航空发动机、核反应堆等**安全和国民经济的重要领域，需要实现1800 ℃以上的高温原位测量。常规石英光纤传感器受限于材料特性，无法在1000 ℃以上高温环境中长期稳定使用。单晶蓝宝石光纤具有极高的熔点（2053 ℃）和较低的传输损耗，是一种良好的高温传感材料。在单晶蓝宝石光纤内部刻写布拉格光栅，可以研制出蓝宝石光纤光栅传感器，具有耐温性能好、测量精度高、便于多点测量等优点，是当前最具发展前景的新型高温传感器件。首先介绍了蓝宝石光纤光栅高温传感器的工作原理和理论模型，接着介绍了利用飞秒激光制备蓝宝石光纤光栅的三种主流技术，包括相位掩模板扫描法、双光束干涉法、直写法，并从制备效率、光谱质量等方面比较了三种技术的优劣，指出飞秒激光直写法是制备蓝宝石光纤光栅高温传感器的最佳手段；然后介绍了蓝宝石光纤光栅的光谱优化方法，包括如何减小光栅光谱带宽和如何降低光谱噪声；进一步介绍了蓝宝石光纤光栅的高温传感特性、封装工艺及高温温度、应变传感应用；最后展望了蓝宝石光纤光栅传感器的未来发展趋势。蓝宝石光纤光栅高温传感器的快速发展和大规模推广应用，必将有助于解决当前我国航空航天、核电等领域重大装备结构健康监测的卡脖子难题。

We demonstrate the fabrication of single-mode helical Bragg grating waveguides (HBGWs) in a multimode coreless fiber by using a femtosecond laser direct writing technique. This approach provides a single-step method for creating Bragg grating waveguides. Specifically, the unique helical structure in such an HBGW serves as a depressed cladding waveguide and also generates strong Bragg resonance due to its periodicity. Effects of pulse energy, helical diameter, and helical pitch used for fabricating HBGWs were studied, and a single-mode HBGW with a narrow bandwidth of 0.43 nm and a Bragg wavelength of 1546.50 nm was achieved by using appropriate parameters, including a diameter of 10 μm and a helical pitch of 1.07 μm. The measured cross-sectional refractive index profile indicates that a depressed cladding waveguide has been created in this single-mode HBGW. Moreover, five single-mode HBGWs with various Bragg wavelengths were successfully fabricated by controlling the helical pitch, and this technique could be used for achieving a wavelength-division-multiplexed HBGW array. Then, the temperature and strain responses of the fabricated single-mode HBGW were tested, exhibiting a temperature sensitivity of 11.65 pm/°C and a strain sensitivity of 1.29 pm/με, respectively. In addition, the thermal stability of the single-mode HBGW was also studied by annealing at a high temperature of 700°C for 15 h. The degeneration of the single-mode waveguide into a multimode waveguide was observed during the isothermal annealing process, and the peak reflection and the Bragg wavelength of the fundamental mode exhibited a decrease of ∼7dB and a “blue” shift of 0.36 nm. Hence, such a femtosecond laser directly written single-mode HBGW could be used in many applications, such as sapphire fiber sensors, photonic integrated circuits, and monolithic waveguide lasers.