Fig. 3: The simulation results of the abnormal-harmonic reflection, beam splitting, and multi-channel retroreflection.

a The schematic of the simulation for abnormal-harmonic reflection at 50° incidence. b The distributions of the electric field in the xoz plane at 50°. c The far-field pattern of the abnormal-harmonic reflection at 50°. d The schematic of simulations for dual-beam splitting. The incident wave is illuminated vertically onto the metasurface, and the reflected wave is divided into two beams radiating into free space at 39° (0th harmonic) and –39° (−2nd harmonic), respectively. e The distributions of the electric field in the xoz plane. f The far-field pattern of the dual-beam splitting. The schematic of simulations for three retroreflective channels: g 0th harmonic corresponding to −39°, j −1st harmonic corresponding to 0°, and m −2nd harmonic corresponding to 39°. The incident plane waves illuminate the metasurface at three retroreflective angles, and the reflected waves are reflected along the same direction. The distributions of the electric field at h −39°, k 0°, and n 39° incidence in the xoz plane. The distributions are all relative electric fields, and the metasurface is placed on the bottom. The far-field patterns at i −39°, l 0°, and o 39° incidence in the xoz plane