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

Abstract

Orbital angular momentum (OAM) beams with different angular indices l have the potential to greatly increase communication 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 multiplexing 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 coaxial 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 fabricated 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.

Ultra-low-loss all-fiber orbital angular momentum mode-division multiplexer based on cascaded fused-biconical mode selective couplers

“…By skillfully integrating phase plates and lenses, it remains possible to construct MDMUXs with acceptable losses and reduced dimensions. [17][18][19][20][21][22] The insertion loss of MDMUX based on a multiphase plane has been as low as 2.6 dB, achieving orbital angular momentum (OAM) MDM with topological charges ranging from 0 to 5. 23 Fiber-based MDMUXs have emerged as captivating methodologies, underpinned by their inherent low loss.…”

Multi-mode polarization-filtering hollow core anti-resonance fiber using SPR

“…Compared to single mode fiber, few mode fiber has some unique applications such as few-mode fiber amplifier [28], mode-division-multiplexed system [29], and multi-parameter sensing [30,31]. Orbital angular momentum beams can dramatically increase communication capacity and spectral efficiency [32], and communication in higher-order modes has potential applications [33]. Higher-order mode polarisation filters have important applications as optical devices in multiplexing techniques for orbital angular momentum and in higher-order mode communication systems.…”