A high spatial resolution distributed optical fiber sensor for high-temperature measurements

One of the advantages of the use of optical fibers for sensing is their ability to perform distributed measurements. Several distributed sensors that measure temperature along optical fibers are already commercially available. All of them are based on Raman thermometry. However, the spatial resolution that they achieve is limited to 1 m, making them unsuitable for applications where higher spatial resolution is needed. Also, their temperature range is very dependent on the behavior of fibers at high temperature, a subject which still needs investigation. In this article, we present a distributed optical fiber sensor that addresses these two issues. On one hand, the combination of Raman thermometry with the time-correlated single-photon counting technique permits the achievement of high spatial resolutions (0.1 m). On the other hand, the use of specially coated fibers allows measurement of high temperatures. We have investigated the system temperature sensitivity and have evaluated the measurement errors introduced by the high-temperature behavior of carbon- and gold-coated fibers. We demonstrate that the system is very appropriate for high-temperature distributed measurements with high spatial resolution.