Simultaneous measurement of refractive index and temperature based on down-taper and thin-core fiber

A Mach-Zehnder interferometer (MZI) based on the cascaded structure of a single-mode fiber (SMF) down-taper and thin-core fiber (TCF) is proposed and experimentally demonstrated. The down-taper acts as mode coupler to excite cladding modes. The extinction ratio of the transmission spectra can reach up to 20dB. By monitoring the wavelength shifts of interference dip1 and dip2, simultaneous measurement of refractive index (RI) and temperature can be achieved. The experimental results show that the wavelengths at interference dip1and dip2 have blue shifts with the increase of RI and red shifts with the increase of temperature. The RI sensitivities at interference dip1 and dip2 are -30.290 nm/RIU and -79.335nm/RIU, respectively. The temperature sensitivities at interference dip1 and dip2 are 0.065 nm/ºC and 0.053 nm/ºC, respectively. The proposed MZI exhibits the advantages of easy fabrication, high extinction ratio, low cost, and simultaneous measurement of RI and temperature, which will make a significant contribution to RI measurement.