Terahertz Dual-Band Dual-Polarization 3-Bit Coding Metasurface for Multiple Vortex Beams Generation

Terahertz technology and vortex beams have demonstrated powerful capabilities in enhancing the channel capacity of communication systems. This work proposes a design strategy of dual-band and dual-function 3-bit coding metasurface based on beam polarization characteristics. The unit cell of the metasurface is composed of two pattern structures, which has the ability to flexibly and independently control the reflection phases of incident plane wave at two frequency bands. The metasurface designed in this work is a combination of two patterns according to the addition operation and the convolution operation. The 3-bit coding metasurface generates two orbital angular momentum (OAM) beams with a deflection of 12.1 degrees with modes l(1) = +1 and l(2) = -1 under the y-polarized incidence at 0.6 THz. Similarly, the designed metasurface produces two OAM beams with a deflection of 16.5 degrees under the incidence of x-polarized wave at 0.9 THz, and the modes are l(3) = +1 and l(4) = -2. The full-wave simulation results agree well with the theoretical predictions, which could prove the correctness and effectiveness of the proposed method. The metasurface designed according to this method has potential applications in multiple-input multiple-output (MIMO) communication systems.