Concentration sensor with multilayer thin film-coupled surface plasmon resonance

A concentration sensor based on silver (Ag)/silica (SiO2)/zirconium anhydride (ZrO2) multilayer structure is proposed. Two dominant dips can be observed in the reflection spectrum, which correspond to different sensing methods. Firstly, it is demonstrated that the coupling between the surface plasmon polariton (SPP) mode and a planar waveguide mode (WGM) leads to the Fano resonance (FR). The induced bonding hybridized modes have ultra-narrow full wave at half maximum (FWHM) as well as ultra-high quality factors (Q). We can achieve a theoretical value of the refractive index sensitivity 167 times higher than conventional surface plasmon resonance (SPR) sensors with a single metal layer. Secondly, the waveguide coupling mode was examined by measuring angular spectra. A deep and sharp waveguide coupling dip was obtained. The experimental results show that with an increase in the concentration of the fill dielectric material in the surface of the system, the resonance dip exhibits a remarkable red shift, and the measured angular sensitivity is 98.04°/RIU.