The stability of optical fiber as strain sensor under invariable stress

In this paper, two types of optical fibers have been selected to analyze their stability based on the ensile experiments, one of which is Phi900 mum tight-buffered optical fiber, another of which is Phi250 mum coated optical fiber. The preliminary experimental results show that both of optical fibers exist the strain lag under the effect of same invariable stress. In the first 24 hours, their strains all increase 5% under invariable stress, and then slow down in the following days. In another experiment, they are both immersed in water. It is found that the tight-buffered optical fiber has a stable measurement, but the coated optical fiber is not stable. It is therefore suggested that the tight-buffered optical fiber be more suitable than the coated optical fiber as the sensible media for the strain monitoring of geotechnical engineering that is usually affected by underground water.