Multiplexing free-space optical signals using superimposed collinear orbital angular momentum states

Abstract

As a proof of concept, we experimentally demonstrate multiplexing of free-space optical signals in multiple channels labeled with different states of orbital angular momentum. The multiplexing process is carried out by a dynamic liquid-crystal spatial light modulator, while the phase function is calculated by an iterative algorithm. A binary amplitude computer-generated hologram serves as a demultiplexer.

Sidelobe-modulated optical vortices for free-space communication

“…Most of them rely on modulating the intensity, frequency, or polarization of light [1]. Since Allen et al first reported that optical vortices (OVs) with helical phase fronts actually carry orbital angular momentum (OAM) [2], the OAM of OVs has been considered as a new degree of freedom for optical encoding in FSO communication systems [3][4][5][6][7][8].Due to the nonradioactivity compared to the electromagnetic wave band used in contemporary communications and the uncertainty relationship inhered between the angle and OAM of OV beams [9], it is difficult for an eavesdropper to detect the transmitted information precisely, thus also showing the advantage in information security. In 2004, Gibson et al demonstrated information transferring with OAM encoding [3,4].…”

“…Most of them rely on modulating the intensity, frequency, or polarization of light [1]. Since Allen et al first reported that optical vortices (OVs) with helical phase fronts actually carry orbital angular momentum (OAM) [2], the OAM of OVs has been considered as a new degree of freedom for optical encoding in FSO communication systems [3][4][5][6][7][8].…”

“…In 2004, Gibson et al demonstrated information transferring with OAM encoding [3,4]. In 2007, Lin et al reported the experiment of FSO signal multiplexing in multiple channels labeled with different states of OAM and an iterative algorithm to design a phase mask for collinearly superposing several OV beams for data transmission [6]. In June 2012, Wang et al utilized the advantages of OAM encoding with four different topological charges (TCs) and 42.8 × 4 Gbit∕s quadrature amplitude modulation (16-QAM) to achieve a 1.37 Tbit∕s aggregated data transmission rate over the meter-length scale [10].…”

Sorting and detecting orbital angular momentum states by using a Dove prism embedded Mach–Zehnder interferometer and amplitude gratings

“…Theoretically, the OAM quantum number could be any value ranging from −∞ to +∞. This property prospects the potential application of the OAM in the information field [2][3][4][5][6][7][8][9][10][11][12][13]. In recent years several groups built information transmission systems based on OAM [8][9][10][11][12][13].…”

Experimental analysis of orbital angular momentum-carrying beams in turbulence

“…Furthermore, a multi-channel laser communication link may use this orthogonal signal basis to support the simultaneous transmission of information from different users, each on a separate OAM channel. 5,6 Realizing the separation of vortices using optical devices is, nevertheless, a matter of current research, because all known methods show advantages and disadvantages. To actually distinguish an OAM state from another, the received vortex has to be analyzed with an optical device capable of canceling the phase dislocation.…”