A robust fiber inline interferometer sensor based on a core-offset attenuator and a microsphere-shaped splicing junction

A robust inline fiber interferometer sensor based on concatenating a core-offset attenuator and a microsphere-shaped splicing junction is proposed, fabricated and applied for sensing applications. Its transmission spectrum shows multiple resonant dips due to the interference between core and cladding modes. While the interferometer sensor is utilized to test surrounding RI from 1.33 to 1.37, it exhibits a linear relationship between peak wavelength shift and RI change. A maximal sensitivity of -56.325 nm/RIU (refractive index unit) is obtained. For temperature sensing, the sensor presents a fair quadric relationship between peak wavelength shift and temperature from 25 to 650 °C, in which the variation rate of the effective RI difference between core and cladding modes with temperature is nonlinear. In addition, a coefficient matrix is constructed to simultaneously measure RI and temperature. The fiber interferometer sensor offers high potential in sensing applications due to its advantages of low cost, simplicity, and robustness.