A Broadband Transmissive Metasurface for Non-Diffractive THz OAM Multiplexing and Communication

Terahertz (THz) orbital angular momentum (OAM) beams have tremendous potential for tackling the capacity crunch in high-speed wireless communication. However, conventional OAM beams suffer from the limitations of beam divergence and stringent alignment requirements in practical wireless communications. To cope with the challenge, we propose a broadband Huygens’ transmissive metasurface for the manipulation of non-diffractive OAM beams operating at 0.1 THz, which has the advantages of low profile, simplicity, and ease of fabrication. By virtue of its flexible phase control capability, the metasurface using a combination of hyperbolic phase, OAM phase, and axicon phase is proposed to multiplex two high-order Bessel beams. Both simulation and measurement results indicate that it generates non-diffractive OAM beams with high purity over a broad bandwidth of 20 GHz. Based on the metasurface, a 112-Gbit/s photonic THz wireless communication link using two non-diffractive OAM beams, with each channel carrying a 14-Gbaud 16-quadrature amplitude modulation (QAM) signal, is experimentally demonstrated for the first time. The communication performance of high-order Bessel beams is compared with the conventional OAM beams, and it is found that these high-order Bessel beams are more preferable to increase the signal-to-noise ratio (SNR) owing to the more stable field distribution. This work provides an effective way to alleviate the diffractive divergence of the OAM waves and extend the achievable link distance in wireless THz OAM communication systems, opening new opportunities for high data rate wireless communications.