Noncoaxially propagating discrete data by coding/decoding orbital angular momentum of vortex beam through multiple channels

A concept of noncoaxially propagating discrete data by coding/decoding orbital angular momentum (OAM) of vortex beam through multiple channels is proposed. Four independent channels along different directions (diffraction orders/angles) are established by a series of specially designed holograms. Sixteen vortex beams are used to code each sequence with the length of 4 bits into an OAM mode in each channel. The theoretical analysis (simulation) demonstrates that the proposed scheme is reliable. In addition, an experiment is also designed and performed for practically certifying the feasibility of the proposed scheme. A 16-bits-length sequence, which is coded into four OAM modes in four channels (one channel with one OAM mode), is successfully received/decoded by observing the intensity-profile arrays (OAM-mode spectrum) generated by a specially designed Dammann vortex grating. The measured results show that the proposed concept is also viable in practice. Moreover, the received/recovered images indicate that the performance of the system decreases as the atmosphere turbulence strength increases when a color image and a gray-scale image are simultaneously propagated. Besides, the measured bit error rate (BER) gradually decreases with the increase of bit rate or propagation distance. The acceptable BER under the threshold of forward error correct can be achieved for a short-distance communication network.