The generation, propagation, and detection of high-quality and coherently superimposed optical vortices, carrying two or more orbital angular momentum (OAM) states, is experimentally demonstrated using an optical arrangement based on spatial light modulators. We compare our results with numerical simulations and show that, in the context of turbulence-free wireless optical communication (indoor or satellite), individual OAM state identification at the receiver of an OAM-modulated system can be achieved with good precision, to accommodate for high-dimensional OAM modulation architectures. We apply our results to the simulation of a communication system using low-density paritycheck-coded modulation that considers optimal signal constellation design in a channel that includes OAM crosstalk induced by realistic (imperfect) detection.

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In a laboratory experiment we generate, propagate, and detect laser vortex beams carrying orbital angular momentum (OAM) by means of spatial light modulators (SLMs). We show that beams with OAM states from -20 to +20 can be effectively generated using different types of phase gratings, and that excellent contrast between adjacent OAM modes is achieved. A weak turbulent air flow is induced on the propagation path to emulate the effects of atmospheric turbulence. By characterizing the effects of optical turbulence on the modal crosstalk among received OAM states we show that it is possible to distinguish them for the purpose of increasing the data throughput of a laser communication link in weak turbulence. It is also demonstrated that by increasing the complexity of the receiver, optical separation of the OAM modes is possible at stronger turbulence conditions.

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