The authors demonstrate a hollow core photonic crystal fiber (HCPCF) surface-enhanced Raman probe consisting of a HCPCF with Au nanoparticles coated on the inner surface of the air holes serving as the substrate of surface-enhanced Raman scattering (SERS). The experimental results indicate that the confinement of light inside the HCPCF and the coating of nanoparticles/analyte inside the air holes of the HCPCF offer a large area for the light to interact with the SERS particles. An optimized design of the HCPCF is provided to further improve the probe sensitivity.

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The formation and propagation of cracks reflect the aging and pathologic changes of concrete structures and may cause problems such as seepage and long-term durability. Crack detection and monitoring is therefore an effective way to evaluate structural health conditions. An important challenge in such a task is that the locations and orientations of cracks in concrete structures are difficult to predict due to material inhomogeneity and complexity. The number of the required conventional electric and electromagnetic sensors to cover all possible cracks may be too large to be practical for a monitoring scheme. In this paper, a fiber optic sensor with distributed crack sensing capability based on optical time domain reflectometry is proposed and its sensing principle is introduced. Experiments are conducted to obtain the optical power loss versus crack opening at different fiber inclination angles, and then a model is developed to quantify it. Finally, an experiment is performed to demonstrate the practical application of the sensor. The test results show that detecting and monitoring cracks with the sensor do not require a-priori knowledge of crack locations and orientations. fiber optic sensor, crack, concrete Citation:Bao T F, Wang J L, Yao Y. A fiber optic sensor for detecting and monitoring cracks in concrete structures.