Inversion of spectral emission measurements to reconstruct the temperature profile along a blackbody optical fiber thermometer

Abstract

A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Standard two-color optical fiber thermometry involves measuring the spectral intensity at the end of the fiber at two wavelengths. The temperature at the sensing tip of the fiber can then be inferred using Planck's law and the ratio of the spectral intensities. If, however, the length of the optical fiber is exposed to elevated temperatures, erroneous temperature measurements will occur due to emission by the fiber. The results presented in this article show it is possible to use additional spectral measurements to account for emission by the fiber and accurately measure the tip temperature. In addition, the proposed technique can be used to obtain an estimate of the temperature profile along the fiber.