Differential FBG sensor for temperature-independent refractive index measurement

We demonstrated a simple method for temperature-independent refractive index measurement by use of two cascaded fiber Bragg gratings fabricated in single-mode fiber and microfiber, respectively. The reflective peaks of the two FBGs exhibit almost identical temperature sensitivity of 10.1 pm/°C and different responses to ambient refractive index. Based on the differential measurement method, of the issue of temperature cross-sensitivity for FBG sensors is solved. The refractive-index sensitivity of the sensor is 17.22 nm/RIU when the diameter of microfiber is 6.5 μm.