Abstract
Orbital angular momentum (OAM) beams, characterized by the helical phase wavefront, have received significant interest in various areas of study. There are many methods to generate OAM beams, which can be roughly divided into two types: spatial methods and fiber methods. As a natural shaper of OAM beams, the fibers exhibit unique merits, namely, miniaturization and a low insertion loss. In this paper, we review the recent advances in fiber OAM mode generation systems, in both the interior and exterior of the beams. We introduce the basic concepts of fiber modes and the generation and detection theories of OAM modes. In addition, fiber systems based on different nuclear devices are introduced, including the long-period fiber grating, the mode-selective coupler, microstructural optical fiber, and the photonic lantern. Finally, the key challenges and prospects for fiber OAM mode systems are discussed.
Highlights
Since Allen first demonstrated the orbital angular momentum (OAM) of light as an independent dimension in 1992 [1], beams carrying Orbital angular momentum (OAM) have attracted increasing interest in various fields
Unlike the conventional plane light wave, OAM modes are characterized by a helical phase front e±ilξ [1], where ± l is the topological charge (TC) and ξ is the azimuthal angle related to the optic axis
The authors of this paper have experimentally demonstrated that using a single cylindrical vector (CV) mode in a two-mode fiber (TMF), the topological charge of generated OAM mode can be switched among −1, 0, +1, as shown in Figure 8e [32]
Summary
Since Allen first demonstrated the orbital angular momentum (OAM) of light as an independent dimension in 1992 [1], beams carrying OAM have attracted increasing interest in various fields. Sci. 2019, 9, x FOR PEER REVIEW index differences in these methods, the conversion processes from incident beams to OAM beams including micro-ring resonators [30], among other as shown. Differences in these methods, the conversion processes from incident beams to OAM beams are not modest, thereby leading to a relatively high insertion loss. Compared with spatial generating methods, fiber generating methods have shown are usually large This indicates that miniaturization and integration of the space systems is advantages. Incident beams of any shapes conversion process is moreinto modest than that spatialsymmetry generating methods, energy will be converted the eigenmodes with in cylindrical under the restrictionthe of fiber. The recent advances in fiber OAM generation systems are given. Cylindrical Vector Modes vector (CV) modes, whose polarization varies based on the spatial location, show
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