Abstract: The rapid development of aerospace， nuclear energy， and advanced manufacturing has increased the demand for reliable high-temperature sensing materials and technologies for extreme environments. Conventional silica fibers suffer from poor thermal stability at high temperatures， while sapphire fibers， although widely used， still face challenges in stable sensing above 1 800 ℃. Lutetium oxide （Lu₂O₃） single-crystal fiber （SCF） is a promising alternative because of its high melting point of approximately 2 490 ℃， excellent thermal stability， and favorable optical properties. It also retains the structural advantages of optical fibers， including a large aspect ratio， small diameter， and potential for device integration， making it attractive for high-temperature sensing beyond the temperature limits of sapphire fibers. In this work， high-quality Lu₂O₃ SCFs with ［100］， ［110］， and ［111］ orientations were successfully grown by the laser-heated pedestal growth method. The fibers are uniform and transparent， with a diameter of 60 μm and a length of 1 m， and show no visible cracks or inclusions， indicating good crystal quality and stable growth. A third-order fiber Bragg grating （FBG） was then fabricated in the ［111］-oriented Lu₂O₃ SCF by femtosecond laser line-by-line scanning. The grating has a length of 4 mm and a period of 1.223 μm， and its reflection spectrum is centered at 1 549.47 nm with a full width at half maximum of 0.843 nm and a signal-to-noise ratio of 15.3 dB， confirming the formation of a well-defined grating structure. The temperature sensing performance of the fabricated Lu₂O₃ single-crystal fiber Bragg grating （LFBG） was systematically investigated over a wide temperature range from 20 ℃ to 1 600 ℃. The grating maintain a stable and repeatable spectral response during both heating and cooling， indicating excellent thermal stability of both the grating structure and the fiber material. As the temperature increase， the reflection peak shift monotonically toward longer wavelengths， with a maximum temperature sensitivity of 23.2 pm/℃ at 1 600 ℃. These results demonstrate that LFBG can maintain stable optical response and reliable sensing performance at high temperatures. Owing to their high melting point， good optical transparency， and compatibility with miniaturized sensing devices， Lu₂O₃ SCF represents a promising platform for temperature sensing in extreme environments， including aerospace engines， nuclear energy systems， high-temperature furnaces， and advanced manufacturing equipment.

Key words: Lu₂O₃ single-crystal fiber; laser-heated pedestal growth method; single-crystal growth; fiber Bragg grating; temperature sensing