Low-crosstalk demodulating vortex beams by a combination of two partial-receiving apertures in free space

In order to improve the performance of a communication system, a novel concept of low-crosstalk demodulating vortex beams by a combination of partial-receiving apertures (PRAs) is proposed. The corresponding theory analysis and simulations are performed for certifying the valid of the proposed concept in theory. A proof-of-concept experiment is also proposed and established to verity the feasibility of the proposed concept in practice. Based on the captured intensity-array profiles in experiments, the total crosstalk, which is induced by partial receiving apertures, can be evenly distributed among the parasitic orbital angular momentum (OAM) modes, then the maximum ratio of intensity between the induced parasitic OAM modes and the propagated OAM modes can be notably decreased when two unsymmetrical PRAs are utilized. The measured bit error rate curves (with respect to the differently-placed PRAs) also show that the performance of system can be improved in sequence when three ways of one PRA, two symmetric PRAs and two asymmetric PRAs are orderly utilized for demodulating OAM beams, respectively. Besides, the measured results also demonstrate that the proposed system performances are declined with the increases of data rates or propagation distances. Consequently, our proposed concept in this paper is valid and reliable in both theory and practice, and then can be used to demodulate the vortex beams with low crosstalk for free-space optical communication in future. (paper)