Multimode OAM Convergent Transmission With Co-Divergent Angle Tailored by Airy Wavefront

Wireless backhaul offers a more cost-effective, time-efficient, and flexible solution than wired backhaul to connect the edge-computing cells with the core network. As the amount of transmitted data increases, the low-rank characteristic of the line-of-sight (LoS) channel severely limits the growth of channel capacity in the point-to-point backhaul transmission scenario. Orbital angular momentum (OAM), also known as vortex beam, is considered as a potentially effective solution for high-capacity LoS wireless transmission. However, due to the shortcomings of its energy divergence and the specificity of multimode divergence angles, OAM beams have been difficult to apply in practical communication systems for a long time. In this work, a novel multimode convergent transmission with a co-scale reception scheme is proposed. OAM beams of different modes can be transmitted with the same beam divergent angle, while the wavefronts are tailored by the ring-shaped Airy compensation lens during propagation, so that the energy will converge to the same spatial area for receiving. Based on this scheme, not only is the signal-to-noise ratio (SNR) greatly improved but it is also possible to simultaneously receive and demodulate OAM channels multiplexed with different modes in a limited space area. Through prototype experiments, we demonstrated that three kinds of OAM modes are tunable, and different channels can be separated simultaneously with receiving power increasing. The measurement isolations between channels are over 11 dB, which ensures a reliable 16-QAM (quadrature amplitude modulation) multiplexing wireless transmission demo system. This work may explore the potential applications of OAM-based multimode convergent transmission in LoS wireless communications.