Extending orbital angular momentum multiplexing to radially high orders for massive mode channels in fiber transmission

Orbital angular momentum (OAM) beams with different angular indices l have the potential to greatly increase com-munication capacity. However, the finite aperture of optical systems limits the value of the angular index. In order to fully use the orthogonal mode channels supported in the fiber for high-capacity communications, we propose extending the radial indices p of OAM modes as an additional multiplex-ing dimension. In this paper, we introduce spatially discrete multiple phase planes to multiplex the angular and radial OAM modes simultaneously. Due to the orthogonal property of the central symmetric OAM modes, a two-dimensional (2D) input Gaussian beams array can be converted to coax-ial OAM modes through Cartesian to log-polar coordinate transformation by inverse design. For a proof-of-concept demonstration, a 10-mode multiplexer for high-order radial OAM modes was designed using five phase planes. The fabri-cated multiplexer generated high-quality multiplexed OAM modes with a loss of less than 5.4 dB. The multiplexed OAM modes were coupled into a specially designed ring-core fiber by mode-field matching, achieving stable mode transmission in 2 km fiber. The approach provides a scalable technology to increase the number of transmission channels and could lead to the practical applications of OAM multiplexing in communication. & COPY; 2023 Optica Publishing Group

Automated summary

To increase communication capacity, the angular indices of OAM beams can be extended by using spatially discrete multiple phase planes to multiplex the angular and radial OAM modes simultaneously. The proposed approach converts a 2D input Gaussian beams array to coaxial OAM modes through Cartesian to log-polar coordinate transformation. A 10-mode multiplexer was designed and successfully demonstrated, achieving stable mode transmission in a 2 km fiber.