Orbital angular momentum (OAM) modes, having unique properties of a helical phase structure and doughnut intensity profile, have been widely studied in fiber-optic communications, in terms of OAM modulation and OAM multiplexing. In general, different types of specialty fibers with a ring-shape structure are preferred for more stable OAM transmission, which, however, may face greater manufacturing challenge and larger fiber loss compared to standard multi-mode fibers (MMFs). Therefore, the widely deployed and commercially available standard MMFs that can support hundreds of OAM modes have recently attracted great attention. In this paper, we review recent research progress in OAM communications based on standard MMFs. First, the basic concept of OAM and different types of specially designed OAM fibers are briefly introduced. Then, the OAM mode properties in MMFs and recent works, including OAM mode modulation, multiple-input multiple-output (MIMO)-free OAM mode group multiplexing, small-scale partial MIMO assisted OAM mode multiplexing, and OAM-based heterogeneous fiber-optic networks, are presented. The OAM communications using other widely deployed standard single-mode fibers are also briefly introduced as supplementary. Finally, key challenges and perspectives of OAM communications based on standard MMF are discussed and summarized.

中文翻译：

---

基于标准多模光纤的轨道角动量通信（特邀论文）

轨道角动量 (OAM) 模式具有螺旋相位结构和甜甜圈强度分布的独特特性，已在光纤通信中在 OAM 调制和 OAM 复用方面得到广泛研究。一般来说，具有环形结构的不同类型的特种光纤是更稳定的 OAM 传输的首选，然而，与标准多模光纤 (MMF) 相比，这可能面临更大的制造挑战和更大的光纤损耗。因此，能够支持数百种OAM模式的广泛部署和商用的标准MMF在近期备受关注。在本文中，我们回顾了基于标准 MMF 的 OAM 通信的最新研究进展。首先简要介绍OAM的基本概念和专门设计的不同类型的OAM光纤。然后，MMF 中的 OAM 模式特性和最近的工作，包括 OAM 模式调制、无多输入多输出 (MIMO) 的 OAM 模式组复用、小规模部分 MIMO 辅助 OAM 模式复用和基于 OAM 的异构光纤网络, 呈现。还简要介绍了使用其他广泛部署的标准单模光纤的 OAM 通信作为补充。最后，讨论和总结了基于标准 MMF 的 OAM 通信的主要挑战和观点。还简要介绍了使用其他广泛部署的标准单模光纤的 OAM 通信作为补充。最后，讨论和总结了基于标准 MMF 的 OAM 通信的主要挑战和观点。还简要介绍了使用其他广泛部署的标准单模光纤的 OAM 通信作为补充。最后，讨论和总结了基于标准 MMF 的 OAM 通信的主要挑战和观点。