Metasurface-Based Enhanced Orbital Angular Momentum Index Modulation for High Spectral Efficiency and Energy Efficiency

With the advantages of providing numerous multiplexing channels and transmitting index symbols without energy consumption, orbital angular momentum (OAM) technology and the index modulation (IM) scheme have become increasingly prominent in improving spectral efficiency (SE) and energy efficiency (EE). In this paper, an enhanced OAM-IM communication system based on the metasurface is proposed for improving both SE and EE. As the generator and demultiplexer for multiplexing OAM beams, the metasurface can not only improve the system bandwidth and reduce system complexity, but also avoid the mode degeneracy problem in traditional OAM-IM systems, thereby significantly increasing the number of available modes. Moreover, the improvement in index rules enabled the increase in the index symbol information and multiplexing channels, further exploiting the potential of the OAM-IM scheme to improve SE. The countermeasures adapted to different modulation formats have been discussed, while the advantages of the enhanced OAM-IM scheme in improving capacity and EE have been verified by simulations. At last, with the joint support of the metasurface and photonics-aided THz communication links, the feasibility and generality of the enhanced OAM-IM schemes have been demonstrated through high-speed communication experiments.