Free-space Optical Multiplexing Scheme Based on Acousto-optic Deflector (AOD) with Orbital Angular Momentum

Free-space optical multiplexing is essential for multimode quantum repeater, which plays a central role in quantum information processing and communication. Regarding spatial degrees of freedom, orbital angular momentum (OAM) modes have garnered significant interest due to their capacity for encoding with infinite inherent dimensions. OAM qubits and optical paths multiplexing have been separately implemented in previous work, the achieved number of multiplexed modes implemented is on the order of hundreds. We propose to directly enhance free-space optical propagation mode by combining optical paths multiplexing based on acoustic-optic deflectors (AODs) with OAM modes. The experiment verified that OAM still maintains high efficiency and considerable 0.5 dB bandwidth after AODs modulation. This scheme at least offers one order of magnitude more mode numbers than previous works and is expected to achieve higher mode numbers in quantum memory using more practical methods.