Abstract
Abstract Structured light has gained much interest in increasing communications capacity through the simultaneous transmission of multiple orthogonal beams. This paper gives a perspective on the current state of the art and future challenges, especially with regards to the use of multiple orbital angular momentum modes for system performance enhancement.
Highlights
In 1992, Allen et al [1] reported that orbital angular momentum (OAM) can be carried by an optical vortex beam
The number of 2π phase changes in the azimuthal direction is the OAM mode order, and beams with different OAM values can be orthogonal to each other. Such structured beams are a subset of the Laguerre–Gaussian (LGlp) modal basis set, which has two modal indices: (1) l represents the number of 2π phase shifts in the azimuthal direction and the size of the ring grows with l; and (2) p+1 represents the number of concentric amplitude rings [2]
Since all the beams are in the same frequency band, the system spectral efficiency is increased. These multiplexed orthogonal OAM beams are a form of mode-division multiplexing (MDM), a subset of space-division multiplexing [4–7]
Summary
In 1992, Allen et al [1] reported that orbital angular momentum (OAM) can be carried by an optical vortex beam. Such structured beams are a subset of the Laguerre–Gaussian (LGlp) modal basis set, which has two modal indices: (1) l represents the number of 2π phase shifts in the azimuthal direction and the size of the ring grows with l; and (2) p+1 represents the number of concentric amplitude rings (see Figure 1) [2] This orthogonality enables multiple independent optical beams to be multiplexed, spatially copropagate, and be demultiplexed – all with minimal inherent cross talk [3–5]. A key question remains as to how this young field may develop over the decade It is in this spirit that this article is aimed, taking an educated guess as to the subjective and relative merits of different aspects of this field. Liu: Perspective on using multiple orbital-angular-momentum beams for communication links
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