Determination of thermal residual strain in cabled optical fiber with high spatial resolution by Brillouin optical time-domain reflectometry

Abstract

The thermal residual strain induced in the cabled optical fiber is a very important factor for evaluating the reliability of optical fiber cables. In order to determine the distributed thermal residual strain in cabled optical fiber, a measurement method based on Brillouin optical time-domain reflectometry (BOTDR) system is proposed in the article. Thermal characteristics of residual strain along cabled optical fibers are investigated theoretically and experimentally based on Brillouin frequency shift (BFS) detection. The thermal residual strain along the cabled fiber, if any, can be determined with a high spatial resolution that is equal to that of the BOTDR system and can be less than a few meters. A double-coated fiber in loose optical cable was used as the test cabled optical fiber, and the experimental results were in good agreement with those predicted from the theory. It has been found that the fiber residual strain increases linearly with decreasing temperature in the range from 50 to −50 °C.