Effect of optical fiber coating on temperature compensation for strain measurement with optical frequency domain reflectometry

The temperature compensation is essential to the strain measurement in distributed optical fiber sensor (DOFS) due to the temperature-strain cross talk. We demonstrated that the temperature sensitivities and characteristics were different among fibers with different coatings. Compared with the uncoated fiber, polyimide coating could increase the temperature-sensitivity coefficient of fibers, while acrylate coating decreases it. The temperature-sensitivity coefficient changed significantly when the fibers were coated with materials due to different thermal expansion coefficient. To study the temperature compensation for stain measurement with DOFS, the experiments were conducted to measure the spectral shifts of scattered light due to temperature and strain changes for acrylate-coated fiber and polyimide-coated fiber bonded to the same steel plate. The temperature-induced strain of steel plate surface was transferred to the optical fibers together with stress-induced strain. Because of different temperature-sensitivity coefficients and fiber coatings, the measured surface strain distributions on the steel plate are different. The expansion coefficient of steel plate measured by polyimide fiber in the experiment was 11.88 x 10(-6) K-1, which coincided with theory value. A hypothesis for analyzing the strain transfer of fiber was found in the experiment. When bonded on the substrate for measuring strain, the total elongation of the fiber is consistent with the total elongation of the substrate along the direction of the fiber within the bonded-length range. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)