High-temperature measurements are of significant importance in various harsh-environment engineering fields, such as fossil fuel production, and the metallurgical and aviation industries. In recent years, there is a steady trend to shift from conventional electronic sensors to optical fiber sensors for high-temperature applications. In particular, optical fiber sensors are small in size, immune to electromagnetic interference, readily applicable for remote sensing, have high elasticity, and incorporate capabilities for multiplexing and distributed sensing. However, commonly used fused silica optical fiber sensors exhibit severe limitations at ultrahigh temperatures due to significantly degraded optical and mechanical properties at temperatures >1000 °C. The excellent optical transparency, thermal and chemical stability, mechanical robustness, and high melting temperature (~2040 °C) of single-crystal sapphire fibers (SFs) make them a strong candidate for sensing applications in high-temperature environments. Translation of the sensing schemes from mature silica fiber sensors to SF sensors has undergone tremendous growth and advancements in the past two decades. However, hurdles to the development of a near-term deployable SF sensing system have proven persistent due to the highly multimodal nature of SFs. This article reviews sensing techniques that have been implemented with SFs recently. The aim is to provide a comprehensive summary of past research on SF sensing systems. Perspectives on further research into the challenging yet promising arena are also discussed.

中文翻译：

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用于高温应用的蓝宝石光纤传感器的进展

高温测量在各种恶劣环境工程领域具有重要意义，例如化石燃料生产、冶金和航空工业。近年来，有一种稳定的趋势，即从传统的电子传感器转向用于高温应用的光纤传感器。特别是光纤传感器体积小，不受电磁干扰，易于应用于遥感，具有高弹性，并具有多路复用和分布式传感的能力。然而，由于在 >1000 °C 的温度下光学和机械性能显着下降，常用的熔融石英光纤传感器在超高温下表现出严重的局限性。优异的光学透明度、热稳定性和化学稳定性、机械强度、单晶蓝宝石光纤 (SF) 的高熔点 (~2040 °C) 使其成为高温环境中传感应用的有力候选者。在过去的 20 年中，传感方案从成熟的石英光纤传感器到 SF 传感器的转换经历了巨大的发展和进步。然而，由于 SF 的高度多模态特性，开发近期可部署 SF 传感系统的障碍已被证明是持久的。本文回顾了最近使用 SF 实现的传感技术。目的是对过去关于 SF 传感系统的研究进行全面总结。还讨论了对具有挑战性但有希望的领域进行进一步研究的观点。