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

•We proposed a Mach–Zehnder interferometer sensor based on a core-offset attenuator and a microsphere junction.•For RI sensing, it exhibits different RI sensitivities using different interference peaks as indicators, which is caused by the contributions of excited minor cladding modes.•For temperature testing, it can be used to measure the temperature up to 650 °C.•A coefficient matrix is constructed to simultaneously measure RI and temperature.

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.