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Mobile traffic growth requires the advancement of not only the wireless access networks but also their backhaul and fronthaul. Terabit-class wireless backhaul and fronthaul can be an alternative to optical fiber transmission and will be one of the key technologies to construct a more flexible and less expensive network infrastructure for sixth-generation mobile networks (6G). However, it is a challenge to provide an extremely high-capacity wireless link for point-to-point connection without spatial multiplexing gain obtained by the multi-path rich environment. We demonstrated the world's highest wireless transmission data rate of 1.58 Tbps in the sub-terahertz (sub-THz) band for 6G backhaul and fronthaul networks on the basis of the orbital angular momentum (OAM) multiplexing technology with a wideband Butler matrix. Terabit-class wireless transmission was achieved by designing a wideband 8×8 Butler matrix with two types of 3-dB couplers for the structure without crossover and differential phase shifters that give the desired phase difference over wide bandwidth. Our Butler matrix is capable of multiplexing eight OAM beams and show a high mode isolation of greater than 15 dB and low insertion loss of less than 1.5 dB from 135 to 170 GHz. We implemented the Butler matrices in our OAM multiplexing transmission system, in which the physical-layer data rate of 1.58 Tbps wireless transmission was confirmed with eight OAM modes and dual polarization using the 32 GHz bandwidth.
Sasaki et al. (Tue,) studied this question.