Self-referenced sensing based on a waveguide-coupled surface plasmon resonance structure for background-free detection

A novel self-referenced sensing method is proposed and studied using a waveguide-coupled surface plasmon resonance structure, where it is shown that two modes supported by this structure could couple to the surface plasmon wave at the sensing surface. Due to the different modal characteristics, these two modes could possess different penetration depths, field enhancements and, therefore, different sensitivities to the surface and bulk background refractive index changes. The self-referenced scheme can then be applied to differentiate these refractive index changes. As the device structure affects the modal properties, its parameters can be optimized to achieve the lowest accumulated system errors. Our analysis reveals that, as one of the SPR modes gets closer to be cut off, the capability of the scheme to correct the background interference could improve.