Simultaneous Measurement of Refractive Index and Temperature Using a Cascaded FBG/Droplet-Like Fiber Structure

A simple and compact sensor based on a cascaded fiber Bragg grating (FBG)/droplet-like fiber structure is proposed for simultaneous measurement of refractive index (RI) and temperature. The sensor can be easily constructed by mechanically bending a section of coating-stripped single-mode fiber at an FBG's pigtail. In the transmission spectrum, two kinds of dips induced by FBG and droplet-like structure are observed. The central wavelength of the dip caused by droplet-like structure is susceptible to both of surrounding RI and temperature, while that caused by FBG is only dependent on temperature. A sensor with a 9.5-mm diameter of droplet-like structure is fabricated and experimentally studied. The experimental results demonstrate the feasibility of the proposed sensor and show that sensor possesses a high RI sensitivity of 157.8891 nm/RIU for the RI range from 1.3330 to 1.3785 and a temperature sensitivity of 10.3 pm/°C.