New Fiber Optic Distributed Temperature Sensor

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Abstract
Several principles for single or multipoint temperature sensing using optical fibers have been proposed but only few are able to give the continuous temperature profile along the way followed by the fiber. One of them, using Raman back scattering, was experimented in various materials and has a wide range but limited resolution, and needs a sophisticated equipment. We report here the experimentation of a new sensor concept based on the bend losses dependance on the temperature, induced by the variation of the refraction-index difference versus the temperature when organic material is used, as for example, in PCS fibers. Because of the sharp variation of the bend losses under strong curvatures, this sensor has a high sensivity (0,2°) over a wide range (at least -20° to +60°C). It is possible to shift this range by matching the radius of curvature. This principle can be applied in a single-point sensor (by measurement of the relative loss) or in a distributed sensor using the optical time reflectometry. It can give a high accuracy in the temperature profile or in the location of a temperature front, with a simple and available end-equipment. However, experiments have shown the non-negligible effect of the back-scattering enhancement and the reliability problems induced by a strong curvature. Various realizations of such a sensor are proposed.© (1987) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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