Orbital Angular Momentum Channel Research Articles

Influence of atmospheric turbulence on optical communications using orbital angular momentum for encoding

We describe an experimental implementation of a free-space 11-dimensional communication system using orbital angular momentum (OAM) modes. This system has a maximum measured OAM channel capacity of 2.12 bits/photon. The effects of Kolmogorov thin-phase turbulence on the OAM channel capacity are quantified. We find that increasing the turbulence leads to a degradation of the channel capacity. We are able to mitigate the effects of turbulence by increasing the spacing between detected OAM modes. This study has implications for high-dimensional quantum key distribution (QKD) systems. We describe the sort of QKD system that could be built using our current technology.

Free-space optical transmission with orbital angular momentum division multiplexing

The experimental demonstration of a free-space optical transmission system with orbital angular momentum (OAM) division multiplexing is reported. Two beams have been multiplexed with different values of the azimuthal index l, and hence carrying different OAM, at a wavelength of 1550 nm. The first beam (l = 0) is nearly Gaussian and it features an OAM equal to zero. The second beam (l = 1) is an optical vortex produced by means of a suitable computer-generated hologram, which shows an intensity pattern with a doughnut shape and possesses an OAM of –h per photon. A binary intensity modulation at 1.25 Gbit/s has been applied to each OAM channel and an interferometer with Dove prisms has been exploited for OAM demultiplexing.