An Efficient Bi-Functional Metagrating via Asymmetric Diffraction of Terahertz Beams

Multifunctional metasurfaces are attracting growing attentions due to the compactness and the flexibility in beam manipulation. A bi-functional metagrating capable of anomalous refraction and beam splitting via asymmetric diffraction is designed, 3D-printed and experimentally verified at 0.14 THz. The asymmetric diffraction behavior is well explained by the excitation-direction-dependent mode amplitude inside the metagrating based on a simplified modal method. The measured efficiency of anomalous refraction towards +70° is 80.7% under + z illumination, and the measured efficiency of beam splitting is 43.7%/39.5% towards -70°/+70° under - z illumination. The method here is further extended to achieve asymmetric diffraction into arbitrarily defined directions. Our work opens a new avenue in developing multifunctional and compact terahertz devices for wavefront shaping via excitation directions.