Thz four-beam steering using metagrating pair with angle insensitivity and tailored geometric symmetry

Abstract

Dynamic multi-beam steering is highly desired in target tracking and networking, with faster speed and larger flexibility as compared to single-beam steering. Here, instead of actively controlling meta-atoms in phased array metasurfaces, four beams are simultaneously scanned by cascaded diffraction of a pair of rotating metagratings. By tailoring the rotation symmetry and azimuth-angle-insensitive diffraction of the metagratings, multiple tangential wave vectors in the two layers are one-to-one added vectorially in order to govern the output four-beam direction. By combining a four-beam splitter metagrating with a beam deflector, we experimentally demonstrate THz four-beam steering with symmetric or asymmetric trajectories. The asymmetric steering shows ± 60° field of view with average efficiency of 41 % by tuning the relative orientation of the two metagratings, and the symmetric steering shows ± 22° field of view with the potential for further increasing the coverage. The efficiency fluctuation of the four beams is less than 4 %. This dynamic multi-beam steering strategy shows great potential for flexible signal transmission and processing in the THz band.