High-dimension data coding and decoding by radial mode and orbital angular momentum mode of a vortex beam in free space

Abstract A novel coding/decoding concept based on the orbital angular momentum (OAM) mode and radial mode of a vortex beam is proposed for short-haul free-space optical communication. Sixty-four kinds of vortex beams, which are comprised of sixteen OAM modes and four radial modes, are employed and utilized for coding each of 6-bits-length sequences into one of the 64-ary symbols. A specially-designed Dammam vortex grating (DVG) is utilized to generate an intensity-array profile, where the received vortex beam is demodulated into Gaussian beam in the related coordinate (order). In one of the coordinates, the received vortex beam can be converted into a bright spot (Gaussian beam) with a certain number of intensity rings. According to the coordinate and number of intensity rings, the received vortex beam can be identified and then decoded into the initially-propagated information sequence. The corresponding theory analysis/simulations and experiments demonstrate that the proposed concept is valid and feasible. In addition, the measured results also demonstrate that the performance of the proposed concept declines as the transmission rate/ atmosphere turbulence strength/propagation distance increases. By adopting advanced devices and approaches, the performance of the proposed scenario can be significantly improved, and then the proposed concept can be potentially utilized for short-haul free-space optical communication in the future.