RARE-EARTH DOPED OPTICAL FIBERS FOR TEMPERATURE SENSING

This paper is a report on the feasibility of using a variety of rare-earth doped optical fibers for measuring spatially averaged temperatures from approximately 0 to approximately 100-degrees-C over distances of 10 to 20 m. Such distributed temperature sensors would be paticularly well-suited for building climate control systems and industrial processing applications. The temperature dependent absorption spectra of 6 MCVD processed fibers containing different concentrations of Nd3+, Pr3+, Sm3+, and Yb3+ rare-earth ions were characterized and used to determine thermally active dopant species, optimal dopant concentrations and most sensitive operating wavelengths for use as dual wavelength distributed temperature sensors. Signal attenuation changes were found to vary linearly with temperature from 0.05 dB/degrees-C to 0.10 dB/-degrees-C for those fibers studied. A real-time temperature monitoring experiment using a Pr3+ fiber was in excellent agreement with a thermocouple for temperature cycling between 21 and 80-degrees-C. The results indicate that a temperature resolution of at least 1-degrees-C is feasible for both Pr3+ and Nd3+ fiber systems.