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High-temperature, chemically harsh processes underpin a wide range of applications ranging from power generation, infrastructure monitoring, chemical manufacturing, and many others. For such processes, in situ sensor data is a valuable tool for both optimization and safety, however, traditional sensor platforms can be limited in terms of stability at high temperatures or under highly corrosive, reducing, or oxidizing chemical conditions. Optical fiber-based sensing offers a unique tool for this type of harsh environment sensing application. Off-the-shelf silica fiber itself is highly stable up to ~800 °C, under a wide range of chemical conditions; while single crystal optical fiber expands this operational range even further, to temperatures well above 1000 °C. Work will be presented on the utilization of n-type semiconducting oxide thin films on single crystal sapphire fiber for the evanescent field-based sensing of reducing gas streams at temperatures up to 900 °C. The role of oxygen defects on the electrical and optical properties of the relevant films will be discussed, providing a theoretical background for the observed sensing response, time-dependence, and stability. Doped SrTiO3 systems (LaxSr1-xTiO3) will be discussed for hydrogen sensing at high temperatures. Strategies and challenges associated with pushing sensor and single crystal fiber performance above 1000 °C will also be discussed.
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