High-Efficiency Generation of Vectorial Terahertz Beams via Surface-Wave-Excited Dielectric Metasurfaces.

Generating pre-designed vectorial beams via on-chip devices can yield many fascinating applications, but traditional diffraction-based devices are bulky and inefficient. While plasmonic metasurfaces exhibit ultra-compact sizes and deep-subwavelength resolutions, their working efficiencies are limited by metallic losses. Here, we propose a generic design for highly efficient, ultra-compact dielectric metasurfaces that generate tailored vectorial beams under surface-wave (SW) excitations, experimentally validated in the terahertz (THz) regime. We first experimentally characterize the basic dielectric meta-atom, and then demonstrate a benchmark meta-device that, under the SW excitation, can generate a circularly polarized focused beam. We next realize two dielectric meta-devices, each consisting of two subsets of meta-atoms responsible for generating two pre-designed circularly polarized beams with opposite helicity, with their interference forming the target vectorial beams. Our experiments show that these two meta-devices can generate an azimuthally polarized Bessel beam and a vectorial multifocal holographic image, respectively. We experimentally show that the present dielectric meta-system exhibits significant improvement in the relevant frequency band compared to its metallic counterpart, and numerically demonstrate that it exhibits an absolute working efficiency as high as 92%. Our study paves the way to realize many on-chip applications with high efficiencies, such as biological sensing, displays, image multiplexing, and beyond.