Multilayered coated infra-red surface plasmon resonance fibre sensors for chemical sensing

Promising potential fields of applications for fibre optic sensors are chemistry, biochemistry and biology [1]; this is based upon the ability of some of these sensors to detect changes in the refractive index in the surrounding medium. Several types of sensors are being investigated such as long period gratings (LPGs), fibre Bragg gratings (FBGs), tilted fibre Bragg gratings (TFBGs) [2]. The majority of these sensors have their highest intrinsic sensitivities for indices over 1.4, which is well beyond the aqueous index. One type of sensor based on surface plasmon resonance (SPR) has shown high spectral sensitivity in the aqueous index regime [4]. There is very little published with regards to multi-layered thin film infra-red SPR fibre devices, and the majority of the papers, such as [5], address the optical properties and not the index sensing potential. In this paper we report on the sensing potential of these infra-red SPR fibre devices using various metal overlay coatings and compare the performance of these sensors to a long period grating sensor. This comparison shows that the SPR fibre sensors out-perform the LPG sensor in the low and aqueous index regime.