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 thei r ability to perform distributed measurements. Several distributed sen sors that measure temperature along optical fibers are already commerc ially available. AU of them are based on Raman thermometry. However, t he spatial resolution that they achieve is Limited to 1 mi malting the m unsuitable for applications where higher spatial resolution is neede d, 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 a ddresses these two issues. On one hand, the combination of Raman therm ometry with the. time-correlated single-photon counting technique perm its the achievement of high spatial resolutions (0.1 m). On the other hand, the use of specially coated fibers allows measurement of high te mperatures. We have investigated the system temperature sensitivity an d have evaluated the measurement errors introduced by the high-tempera ture behavior of carbon- and gold-coated fibers. We demonstrate that t he system is very appropriate for high-temperature distributed measure ments with high spatial resolution. (C) 1997 American Institute of Phy sics.