Titanium dioxide (TiO2) coated optical fiber-based SPR sensor in near-infrared region with bimetallic structure for enhanced sensitivity

A multimode optical fiber-based surface plasmon resonance (SPR) sensor is proposed and theoretically analyzed by using the finite element method (FEM) and transfer matrix method (TMM) based numerical simulations. A bimetallic structure of silver (Ag) and gold (Au) is used as SPR active material, followed by titanium dioxide (TiO2) layer. The TiO2 material is used as a dielectric to enhance the proposed sensor's performance with optimized thickness. The results show that the properties of the proposed sensor are highly dependent on the width of the metal and dielectric coatings, which allows the resonance wavelength tuning. For an aqueous solution of the analyte with a refractive index of 1.37 RIU, the maximum sensitivity of the optimized structure was found to be 14,340 nm/RIU, with a figure of merit (FOM) of 35.7 RIU−1 theoretically. The sensitivity of the sensor and FOM is improved on state of the art, ultimately opening new windows of study in the areas of chemical sensing.