Refractive Index and Temperature Sensor Based on D-Shaped Fiber Combined With a Fiber Bragg Grating

A novel D-shaped fiber structure combined with a fiber Bragg grating for refractive index (RI) and temperature sensing is proposed and experimentally investigated. Thanks to the etched cladding of D-shaped fiber, the resulting interference is strongly influenced by the surrounding refractive index. By monitoring the dip wavelength of D-shaped fiber structure, the refractive index can be measured. Theoretical analysis and simulations were conducted to investigate the cladding mode propagating behavior influenced by the surrounding RI. Combined with the temperature sensing property of fiber Bragg grating (FBG), the possibility of simultaneously measuring the RI and temperature relies on monitoring the resonance dip of the D-shaped fiber modal interferometer and the Bragg wavelength of the FBG. Experimental results showed that the RI sensitivity of -31.79 nm/RIU within the range of 1.333 ~ 1.428, and a temperature sensitivity of 28.7 pm/°C can be obtained. The proposed sensor with simple configuration, low cost and easy fabrication is suitable for refractive index and temperature sensing applications.