Orbital Angular Momentum Multiplexing Using Radio Wave and its Extension to Multishape Radio

Orbital angular momentum (OAM) is a physical property of electromagnetic waves characterized by a helical phase front in the propagation direction. Much research has been conducted using not only light waves but also radio waves for OAM multiplexing. This paper explores the potential of OAM multiplexing using radio waves toward the 6G era. In particular, we study OAM multiplexing as an enabler for high-capacity wireless transmission that allows terabit-class wireless transmission. Different from optical fibers where each OAM carrying beam is reflected within the fibers, the energy of OAM-carrying beams is not necessarily focused within the reception antenna area when OAM multiplexing has been performed due to its divergence. To address this, we propose OAM-MIMO (multi-input and multi-output) multiplexing that uses multiple sets of lower OAM modes with additional digital signal processing. We experimentally validated the effectiveness of the proposed OAM-MIMO multiplexing using 28 GHz and 40 GHz frequency bands by achieving over 100 Gbit/s transmission at a distance of over 100 m. Also, we successfully demonstrate the feasibility of OAM multiplexing using the sub-THz frequency band by achieving over 100 Gbit/s. Finally, we extend our work to multishape radio that exploits the various physical properties of electromagnetic waves. Together with the utilization of OAM, multishape radio will lead to new opportunities toward the 6G era.