Optical properties and long-term stability of unclad single crystal sapphire fiber in harsh environments

Sapphire optical fiber is an excellent candidate for harsh environment sensing due to its high melting point, small size, and chemical resistance. Various optical sensors in sapphire fiber have been explored for decades. However, there is still lack of accurate data on sapphire fiber optical properties at elevated temperatures, which impedes the development of sapphire fiber sensors. In this paper, we fabricate single crystal sapphire fiber via a laser heated pedestal growth system and measure the optical properties of our fiber from room temperature to 1500 ℃ in ambient air and in different gas environments.