Development of a Single Crystal Fiber Probe for Raman Distributed Temperature Sensing above 1000°C

Optical fiber-based sensing is uniquely qualified for a wide range of harsh environment applications due to the ability of optical fiber to withstand high temperature or chemically corrosive conditions. While off-the-shelf silica fiber is stable up to 800-900 degrees C under a wide range of conditions, single crystal fiber offers a pathway to operation above 1000 degrees C. Current single crystal fiber growth techniques are limited to producing multimode fiber, which limits interrogation approaches to primarily time-domain techniques. Raman-based distributed temperature sensing is one time-domain technique which has demonstrated significant utility for distributed temperature sensing in conjunction with multimode, single crystal fiber. A distributed temperature sensor based on Raman scattering and consisting of a single crystal probe spliced to an arbitrarily long silica lead is considered for operational environments up to 1400 degrees C. The impact of temperature and wavelength-dependent optical loss on the measured temperature is investigated, particularly at temperatures above 1000 degrees C. Strategies for improved performance at extreme temperatures are also discussed.