Experimental demonstration of surface plasmon resonance enhancement of the tapered optical fiber coated with Au/Ti thin film

Dependence of taper angle of the surface plasmon resonance (SPR)-based fiber optic sensor on the SPR absorption and sensitivity was investigated. The SPR wavelength was found to increase from 700 nm to 1200 nm with the increase of the refractive index of the surrounding oils from 1.404 to 1.434. The SPR sensitivity increased with the increase of metal-coated taper angle (Ω) from 0.07° to 1.86° by changing the down/up tapering length or waist diameter. The absorption intensity of the SPR spectrum was found to decrease and the FWHM was broadened with the increase of refractive index of the index matching oils (n = 1.404-1.434) due to the leakage of the power fraction of guided rays into the surrounding medium and the spatial spreading and scattering of the conduction electrons, respectively.