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We demonstrate a method for fabricating a fiber sensor which is based on the Mach-Zehnder interference principle and used to the curvature sensing. By using of the CO2 laser fusion, a standard single-mode fiber surface forms a collapse, which is asymmetrical in the normal direction. When the core mode of the transmitted light enters the fusion region, a portion of the light will enter the cladding of the fiber and transport as cladding modes. The cladding modes are sensitive to the external environment and the deformations of the structure. When the cladding modes leave the fusion region, they are re-coupled into the core. Mach-Zehnder interference occurs between the cladding modes and the core mode. The transmission spectrum of the sensor at 1460 nm changes with the curvature. The average sensitivities of the sensor to curvature sensing on the two directions are up to 4.941nm/m-1 and -1.933nm/m-1. This characteristic of the sensor could be used to sense the degree and direction of the curvature of constructions. The curvature sensor we proposed is simple, reproducible and low-cost. It offers a promising applications in construction health monitoring.
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