Enhanced surface plasmon polariton propagation length using a buried metal grating

We report an enhancement in the propagation length of surface plasmon polaritons (SPPs) on a metallic grating when the grating is buried in the substrate. A template-stripping technique has been used to fabricate the buried grating. Near-field measurements on the buried and an exposed grating show that the full width at half maximum of the surface plasmon resonances are reduced to 57% for the prism-coupled SPPs and 77% for the grating-coupled SPPs. The reduction in the full width at half maximum is attributed to a decrease in the in-plane directional scattering of the SPPs on the buried grating. The propagation lengths of the SPPs measured beyond the gratings are close to the theoretical SPP propagation length on an ideal gold surface. The buried grating with a significant reduction in the full width at half maximum of the surface plasmon resonances is theoretically shown to improve the figure of merit of grating-incorporated SPR sensors.