Refractive index sensor for ultra-thin layer based on short range surface plasmon polariton hybrid coupler

A highly integrated sensor based on the hybrid coupler, which is comprised of the short range surface plasmon polariton (SRSPP) and dielectric waveguides, is proposed for ultra-thin layer detection. The dependence of the coupling efficiency between SRSPP and dielectric waveguide mode on the refractive index change of detecting layer is analyzed theoretically. For a detecting layer thinner than 1/10 wavelength, the refractive index resolution can be high up to 5.5×10⁻⁶ RIU with large sensing range as 5×10⁻² RIU and rather short sensing length as tens of microns.