Fibre optic chemical sensor based on surface plasmon monochromatic excitation

A simple fibre sensor for continuous monitoring of refractive index variations of liquid mixtures is described. The transducer is a multimode optical fibre which has been metallized on the sensing area. The principle of this sensor is based on a surface plasmon resonance excitation at the metal (silver)-dielectric interface. This sensor can be used in a range of refractive index from 1.355 to 1.410. The characteristics of this inexpensive sensor, which uses a monochromatic light source, are reported, and the effects of some intrinsic parameters of the optical fibre sensor (length and thickness of the metal layer) are discussed. Both linearity and sensitivity of response of this sensor are presented. This sensor can detect a refractive index variation as small as 3.5 x 10(-5).