D-shaped single mode fiber SPR sensor for measuring RI and temperature simultaneously

We propose and demonstrate a two-channel surface plasmon resonance (SPR) sensor based on a D-shaped single mode fiber (SMF) for measuring refractive index (RI) and temperature simultaneously. The sensor is based on a SMF which is side-polished until the fiber core is exposed properly. By coating an appropriate thickness of gold film on the polished region, SPR phenomenon is formed. To determine the parameter and optimize the performance, we research the RI sensing characters by simulation and experiment at first. The research shows that when the RI increases from 1.333 to 1.410, the sensitivity increases from 1543 nm/RIU to 6300 nm/RIU. And when the thickness of gold film increases from 40nm to 60nm, the resonance wavelength redshifts about 40nm. Based on the research described above, to assemble the sensor, the side-polished region of the SMF is divided into two parts and coated different thickness of gold film to avoid crosstalk. Then by coating the thermo-sensitive material polydimethylsiloxane (PDMS) on one half of the sensing region, this sensor can achieve simultaneous measurement of RI and temperature for temperature compensation. The experiment shows that in the range of 1.333 to 1.390, the RI sensitivity is up to 2260.1 nm/RIU. In the range of 20°C to 60°C, the temperature sensitivity is up to -2.41 nm/°C. This research significantly improves the accuracy of RI measurement for the SPR fiber sensor in practical application by temperature compensation.