Free space optical communications using concentric vortex beams

In this paper, information transmission employing concentric vortex beams is experimentally demonstrated. Concentric vortex beams with different topological charges and different diameters are generated using a spatial light modulator (SLM) loaded with desired diffraction gratings. The proposed method is based on multiplexing and demultiplexing concentric vortex modes with different diameter. In the receiver unit, the mode sequence which encodes data based on the diameters of the concentric vortex beams is recorded by a CCD camera. The operation of the proposed communication link are evaluated experimentally by transmitting a 50 × 50 pixel gray scale image over 3.5m free space. The effects of the atmospheric turbulence on the proposed communication linked are simulated and the crosstalk matrices are evaluated for different levels of the turbulence. Different degrees of freedom can be generated as different modes by controlling the grating characteristics such as topological charge and grating curvature. In this paper, the vortex beam diameters are chosen for decoding purpose.