Jie Liu, Zelin Ma, Junyi Liu, Jiakai Dong, Haolin Zhou, Shuqi Mo, Lixun Wu, Suqing Li, Yujie Chen Yujie Chen, Leslie Rusch, Sophie LaRochelle, Siddharth Ramachandran, Siyuan Yu
This paper presents a comprehensive review of the research efforts in harnessing orbital angular momentum (OAM) modes for space-division multiplexed (SDM) optical fiber communications, including both multi-core and mode-division approaches. With their inherent characteristics of rotational invariance, modal intensity uniformity, and manageable modal degeneracy, OAM modes uniquely enable ultra-high-capacity transmission while significantly mitigating inter-channel crosstalk and simplifying system architecture. Underpinned by these advantages, remarkable progress has been made across the critical components of OAM-based systems: advanced fibers supporting high-density low-crosstalk propagation of high-order OAM modes across distances of tens to hundreds of kilometers, high-performance scalable multiplexers and demultiplexers, and optical amplifiers with equalized modal gain. Collectively, these innovations have promoted OAM-based SDM systems to a technological level characterized by petabit-per-second capacities and ultra-high spectral efficiencies, longer transmission reaches, with low and manageable MIMO processing complexity. Together, they position OAM technology as a transformative solution to the capacity bottlenecks of conventional single-mode fibers, paving the way for the next generation of high-density, energy-efficient optical networks.