Figure-of-merit enhancement of surface plasmon resonance sensors in the spectral interrogation.

We show that adding a thin dielectric layer with high refractive index on top of the metallic layer in surface plasmon resonance sensors in the Kretschmann-Raether configuration in the spectral mode causes a redshift of the resonance wavelength, narrowing of the resonance dip, and an enhancement to the spectral sensitivity. Surprisingly, together with the sensitivity enhancement, the dip becomes much narrower and the figure of merit is considerably improved, particularly in the IR range.