Effect of ultra-shallow metallic gratings on sensitivity enhancement of Goos-Hänchen shift in SPR-based sensors

Abstract

Metallic gratings have flexible and powerful modulation effects on electromagnetic waves. Reflection and transmission spectra of metallic gratings may become extremely narrow or ultra-wide depending on the grating parameters. In this paper, a surface plasmon resonance-based sensing system comprising of a metallic grating coupled with a prism configuration was proposed. The effects of all parameters of the sensing system on the Goos-Hänchen shift and sensitivity were studied in detail, and the results showed that ultra-shallow metallic gratings with large duty cycles, with no other materials involved, are more beneficial. In addition, a set of optimum parameters was obtained at the incident wavelength. Compared with the conventional SPR-based gold sensing chip, strongly coupled surface plasmon resonance around the grating enlarges the penetration depth, and enhances both Goos-Hänchen shift and the corresponding sensitivity by 5.6 times, with increasing refractive indices of the analyte solutions. These results indicate that the proposed ultra-shallow metal grating-based sensing structure is in favor of detecting ultralow concentrations of biomolecules in the analyte solutions.