Bipolarization-controlled metasurfaces for broadband vortex and Airy beam shaping

Terahertz (THz) special beams, such as vortex beams and Airy beams with unique field distributions and diffraction characteristics promote the advancements in wireless information transmission. Metasurfaces with subwavelength thickness and tailorable structures provide a versatile platform for generating these exceptional beams. Nevertheless, these generators typically exhibit complex structures, narrow bandwidth, and single-polarity waveform control. Here, we propose two metasurfaces based on identical bipolarization-controlled meta-atoms that can generate desirable circularly polarized (CP) vortex beams and linearly polarized (LP) Airy beams over broadband. The meta-atom is a reflective metal-dielectric-metal structure composed of an 8-shape-liked pattern on the top metal layer. The phase-only modulation and simultaneous amplitude-phase modulation are achieved just by spatially varying the orientation of the top metal layer. As demonstrations, the application of single-order and multi-beam vortices based on Pancharatnam-Berry phase are produced under the illumination of CP waves ranging from 0.96 to 1.75 THz. The full coverage of amplitude-phase are realized for LP waves incidence when the rotation of top metal layer is set from -45 degrees to 45 degrees. On this basis, one-dimensional and two-dimensional Airy beams with quasi-nondiffracting, self-bending, and self-healing properties are validated respectively. The design opens possibilities for application in high-capacity, obstacle-avoidance wireless communication.