Optimization of tapered optical fiber sensor based on SPR for high sensitivity salinity measurement

High sensitivity detection of seawater salinity has important practical significance. SPR fiber optic sensors based on tapered fiber optic have high sensitivity to refractive index and are widely used in fields such as physics, chemistry, and biology. In this paper, a tapered fiber optic was prepared using a fusion tapering process, and the morphology of the SPR sensor was optimized by adjusting three important parameters: taper length, waist diameter, and coating thickness. The influence of these factors on the sensor performance was studied through simulations. Based on the quality factor as the main evaluation criterion, a tapered fiber optic SPR sensor with a taper length of 27 mm, waist diameter of 25 μm, and coating thickness of 40 nm (Au) was selected through experiments. This sensor was used to detect seawater salinity, and its sensitivity reached 0.708 nm/‰ with good linearity. The experiment also proved the long-term effectiveness of the sensor.