Simultaneous Measurement of Refractive Index and Temperature Based on NFN Structure

We propose and demonstrate a compact all-fiber sensor for simultaneous measurement of temperature and refractive index (RI), which is based on a no-core fiber (NCF) and fiber Bragg grating (FBG). Two segments of NCF used as beam splitter and combiner are embedded on the two ends of an FBG, which constitute a Mach-Zehnder (MZ) interferometer susceptible to the temperature and an ambient RI. With the change of RI and temperature, MZ interference and Bragg reflection result in the variation of transmission spectrum. The experimental results show that the sensitivity of RI is -109.573 nm/RI in the range from 1.333 to 1.398, and the sensitivity of temperature ranging from 10 °C to 70 °C is 0.014 nm/°C, respectively. The feasibility of simultaneous measurement of an external RI and the temperature with this configuration has been demonstrated experimentally.