Simultaneous measurement of temperature and refractive index based on a spherical structure cascaded with thin-core fiber

Abstract

A novel fiber-optic sensor for simultaneous measurement of temperature and refractive index (RI) has been proposed. The sensor consists of a structure of lead-in single-mode fiber (SMF)–spherical structure–middle section SMF–thin-core fiber–lead-out SMF. The spherical structure acts as optical coupler, and excites the cladding modes. The extinction ratio of the transmission spectra can reach up to 20 dB. The experimental results indicate that the temperature sensitivities at interference dip1, dip2 and dip3 are 0.037 nm °C−1, 0.046 nm °C−1 and 0.048 nm °C−1 within the temperature range from 25 °C to 70 °C, respectively, and the RI sensitivities at interference dip1 are −22.111 nm/refractive index unit (RIU) within the RI range from 1.3330 to 1.3496 and −72.584 nm/RIU within the RI range from 1.3496 to 1.3757. The RI sensitivities at interference dip2 and dip3 are 52.679 nm/RIU and −39.803 nm/RIU, respectively, within the RI range from 1.3330 to 1.3797, respectively. Given the large difference in RI between interference dip2 and dip3, simultaneous measurement of temperature and RI can be achieved by monitoring the wavelength shifts of interference dip2 and dip3. The proposed sensor has the advantages of easy fabrication, low cost, and good mechanical strength, and has potential applications in physical, biological, and chemical sensing.