Orbital angular momentum communications based on standard multi-mode fiber (invited paper)

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.