Gold-coated optical fiber-micro-tapers for sensor applications based on the surface plasmon resonance effect

Sensors based on the surface plasmon resonance phenomenon have particular importance in the study of bio-chemical reactions due to their high sensitivity to small refractive index changes in the surrounding medium. The combination of this effect with optical fiber configurations allows particularly miniaturized versions, especially in the form of fiber tapers. We describe a novel, fully symmetrical deposition method for deposition of a gold layer circularly around the taper waist, based on a sputtering technique and usage of a gold-ring target. With such a circular symmetric coating the plasmon resonance effect in the taper becomes completely independent of the polarization of the illumination light. Furthermore, we present numerical calculations of the effects of the taper waist diameter, gold film thickness and analyte interaction length on the plasmon resonance wavelength spectrum. Especially the sensitivity of the analyte refractive index on the plasmon resonance wavelength shift is investigated. Modeling results are compared with experimental data from gold-coated fiber-micro-tapers as sensing element.

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