In-Line Hybrid Fiber Sensor for Curvature and Temperature Measurement

We proposed and demonstrated a compact inline optical fiber sensor for curvature and temperature measurement with low cross sensitivity. The device consists of a 5 mm long hollow-core fiber (HCF) spliced between two single-mode fibers. Two up-tapers were fabricated at each splicing joint forming a Mach-Zehnder Interferometer (MZI). The HCF acted as the anti-resonant reflecting optical waveguide (ARROW), giving periodic dips at resonant wavelengths in the optical transmission spectrum. The cross sensitivity of curvature and temperature problem is solved by demodulating the wavelength shift of the MZI for temperature sensing and intensity variation of ARROW dips for curvature sensing. The curvature and temperature sensitivities are experimentally measured to be -4.28 dB/m
^-1
and 25.76 pm/°C, respectively. The cross sensitivities for ARROW is measured to be 0.0056 m
^-1
/°C. The structure of the sensor is simple and compact, which can be used for structural health monitoring in a complex environment.