Optimization for Closed-Loop Surface Plasmon Resonance Fiber-Optic Refractive Index Sensors Based on Tapered Probes

For the sake of optimizing its measure range,sensetivity and linearity,a tapered Surface Plasmon Resonance(SPR)fiber probe was applied as the substitution of the uniform fiber probe because of its abundant lossy modes.Simulation results and experimental data shew that this tapered probe had a SPR asorption spectrum with better symmetry and its resonance wavelength could change responsing to a bigger range of measured refractive index with a stable wavelength resolution.After constructing a closed-loop SPR fiber sensors based on the tapered probe according to frequency modulation principle,the deionized water sucrose and ethanol solution,whose refractive index value ranged from 1.33 RI unit(RIU)to 1.43 RIU with different concentration,were elected as measurand.The measured results were analyzed and verfied using an Abel refractive index meter.The experimental results demonstrated that the closed-loop SPR fiber-optic sensors with a tapered SPR probe had the sensitivity of 0.00003 RIU,wavelength resolution of 4500 nm/RIU and with better performance in terms of dynamic range,sensetivity and linearity,than that with a uniform SPR probes.