Implementation and Evaluation of sub- THz OAM Multiplexing Transmission

This paper presents orbital angular momentum (OAM) multiplexing transmission with Butler matrices implemented on a sub-terahertz (sub- THz) band for the first ever to our best knowledge. Sub- THz bands enable us to utilize a wide frequency bandwidth for high-capacity wireless transmission. However, the baud rate becomes extremely high as the bandwidth widens, so digital spatial equalization becomes a significant hurdle for implementation. We therefore consider it practical to move part of the function over to analog devices. A Butler matrix is an analog device that can perform discrete Fourier transform (DFT) calculations, and a combination of the Butler matrix and uniform circular array (UCA) can be used to perform the generation and separation of OAM waves. In this paper, we present 4×4 Butler matrices for the generation and separation of four OAM waves (OAM modes 0, ±1, 2) and demonstrate a physical layer data rate of more than 100 Gbit/s for OAM multiplexing transmission over a 10-GHz bandwidth on a sub-THz band.