Refractive Index Measurement of Liquids Using A Dual-color Optical Fiber SPR Sensing System

In this paper we present practical capability of a dual-color optical fiber surface plasmon resonance (SPR) sensing system for measuring the refractive index (RI) of liquids. The sensor system consists of two LEDs, two optical couplers, a photodiode and an electronics followed by a laptop computer via an A/D converter. Features of the developed system are compact, portable and inexpensive. Principle of the proposed SPR sensing system is based on the differential reflectance method. Changes of reflectance at two wavelengths are proportional to the refractive index change of a sensed medium. Differential of two reflectance gives two-folded sensitivity. Three liquids with different RI ranges were tested. Also the reproducibility of measured data was checked. As a result, it was demonstrated experimentally that the dual-color optical fiber SPR sensing system is capable of measuring the RI of liquids over the range of from 1.329 to 1.36 with the RI resolution of 2.35 X 10^-4.