Integrated fiber-optic sensor based on inscription of FBG in seven-core fiber for curvature and temperature measurements

An integrated fiber-optic sensor with cross-sensitivity elimination effect is proposed and experimented for simultaneous measurements of curvature and temperature. The sensor structure mainly consists of a section of seven-core fiber (SCF) that fiber Bragg gratings (FBGs) were inscribed in each fiber core by phase-mask tech-nique. Since the FBG in the central-core of SCF is only sensitive to temperature, and others in six outer-cores have same temperature responses and different sensitivity for curvature, the sensor can simultaneously measure temperature and curvature through analyzing the wavelength shifts of central-core FBG and every-two cores of FBG. The experiment results show that the maximum curvature sensitivity reaches 0.39 nm/m- 1 in the curvature range of 2.53 m- 1-8.62 m-1, and temperature response sensitivity is 9.97 pm/degrees C, which is consistent with or-dinary single-mode FBG in temperature range of 30 degrees C-70 degrees C. Furthermore, the verified experiment for simul-taneous measurement are performed, the central-core FBG can be used as a temperature calibration during the curvature measurement. The relative errors of curvature and temperature are 2.22 % and 2.58 %, respectively. The SCF-based FBG sensor has the advantages of small dimension, easy fabrication, better repeatability, and potential application values in many fields such as machine structure motion monitoring.