Research on simultaneous measurement of temperature and refractive index based on thin-core fiber and pokal taper

An in-line optical fiber sensor is proposed and demonstrated for simultaneous measurement of temperature and refractive index (RI). This sensor can be obtained by splicing two pokal-taper structures and a segment of thin-core fiber (TCF). The middle segment of the TCF works as the sensing region, and the two pokal-taper structures work as an exciter and a coupler. The transmission spectra formed by different lengths of TCF are analyzed theoretically, and then the appropriate length is selected during the experiment. The purpose of simultaneous measurement of temperature and RI can be achieved due to the different parameter responses of the two dips used in the experiment. The sensitivities of the two dips are 0.082 and 0.086 nm/°C in the temperature range of 20°C to −20°C. The sensitivities of the two dips are −43 and −30.83 nm/RIU in the RI range of 1.335–1.37. The proposed sensor has many advantages and wide application prospects.