Sensor based on macrobent fiber Bragg grating structure for simultaneous measurement of refractive index and temperature

A novel and compact all-fiber sensor based on a macrobent fiber Bragg grating (FBG) structure for simultaneous measurement of refractive index (RI) and temperature is proposed and experimentally investigated. The sensor can be easily fabricated by properly bending an FBG. The bending causes interference between the core mode and the whispering gallery mode, which induces another kind of dip in the transmission spectra of the sensor besides the sharp one of the FBG. Because the two kinds of dips respond differently to the surrounding RI and temperature, these two parameters can be unambiguously measured by the sensor. A sample sensor was fabricated and experimentally investigated, and RI sensitivity of 165.9276 nm/RIU in the range from 1.3330 to 1.3785 and temperature sensitivity of 31.7 pm/°C were achieved. This sensor provides a convenient and economical way for applications where temperature and RI have to be simultaneously measured.