We use computational approaches to explore the role of ahigh-refractive-index dielectric TiO2 grating with deep subwavelength thicknesson InSb as a tunable coupler for THz surface plasmons. We find a series ofresonances as the grating couples a normally-incident THz wave to standingsurface plasmon waves on both thin and thick InSb layers. In a marked contrastwith previously-explored metallic gratings, we observe the emergence of a muchstronger additional resonance. The mechanism of this giant plasmonic resonanceis well interpreted by the dispersion of surface plasmon excited in theair\TiO2\InSb trilayer system. We demonstrate that both the frequency and theintensity of the giant resonance can be tuned by varying dielectric gratingparameters, providing more flexible tunability than metallic gratings. Thephase and amplitude of the normally-incident THz wave are spatially modulatedby the dielectric grating to optimize the surface plasmon excitation. The giantsurface plasmon resonance gives rise to strong enhancement of the electricfield above the grating structure, which can be useful in sensing andspectroscopy applications.
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