Temperature compensated curvature sensor with insensitive axial strain based on tapered ring core fiber interferometer

An all fiber temperature compensated curvature sensor with insensitive axial strain is proposed and experimentally demonstrated. The sensor is fabricated by a 2 cm ring core fiber (RCF) which is spliced between single mode fibers (SMFs) with two up-tapers, and a Mach–Zehnder Interferometer (MZI) is formed. The simulation results show that the first up-taper scatters a portion of the input light that should be in the ring core into the outer cladding, and then the ring core modes interfere with the cladding modes distributed in both inner cladding and outer cladding. The interference dips of this structure respond differently to curvature and temperature, so a calibration matrix can be established to implement temperature compensation. Experimental results show that this structure offers a maximum curvature sensitivity of −3.504 nm/m−1 in the range from 1.316 m−1 to 2.372 m−1 with a high linear regression coefficient value of 0.9971, and a maximum temperature sensitivity of 59.42 pm/°C is obtained in the range from 25 °C to 60 °C. We also test the axial strain characteristics of this structure and the results imply a minimum cross sensitivity of 8.086 × 10−5 m−1/με which is extremely low. This indicates that our sensor has axial strain insensitivity which will improve its measurement accuracy. •A curvature sensor based on ring core fiber and dual up-tapers is proposed and experimentally demonstrated.•The proposed curvature sensor can be temperature compensated by a calibration matrix.•The curvature sensor is insensitive to axial strain.•The maximum curvature sensitivity and temperature sensitivity are −3.504 nm/m−1 and 59.42 pm/°C respectively.•Sensors with different ring core fiber lengths and diameters of up-taper are studied.