This research reports a distributed fiber optic high-temperature sensing system tailored for applications in the steel industry and various other sectors. Recent advancements in optical sensor technology have led to the exploration of sapphire crystal fibers as a solution for sensing in harsh environments. Utilizing a femtosecond (fs) laser, cascaded fiber Bragg gratings (FBGs) were meticulously fabricated within a multimode sapphire optical fiber. These FBGs endowed the system with distributed sensing capabilities and underwent rigorous testing under extreme temperatures, reaching up to 1,800 °C. The study delves into the investigation of the FBG reflection spectrum, facilitated by the development of a sophisticated multimode demodulation system, which contributed to the attainment of precise temperature measurements with a performance accuracy of 99.9%. Demonstrating exceptional thermal stability, the sapphire FBGs endured temperatures of 1,600 °C for a sustained duration of 22 hours. Furthermore, the paper explores the application of distributed temperature sensing employing multiple sapphire FBGs, showcasing their utility in temperature measurements related to molten steel studies.


Electrical and Computer Engineering

Second Department

Materials Science and Engineering

Keywords and Phrases

femtosecond (fs) laser; Fiber Bragg gratings (FBGs); Fiber gratings; fiber sensors; molten steel; Optical fiber networks; Optical fiber sensors; sapphire optical fiber; Sensors; Steel; submerged entry nozzle (SEN); Temperature measurement; Temperature sensors

International Standard Serial Number (ISSN)

1557-9662; 0018-9456

Document Type

Article - Journal

Document Version


File Type





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Publication Date

01 Jan 2023