Orbital angular momentum (OAM) carried electromagnetic waves have the potential to improve spectrum efficiency in optical and radio-frequency communications due to the orthogonal wavefronts of different OAM modes. However, OAM beams are vortically hollow and divergent, which significantly decreases the capacity of OAM transmissions. In addition, unaligned transceivers in OAM transmissions can result in a high bit error rate (BER). The Talbot effect is a self-imaging phenomenon that can be used to generate optical or radio-frequency OAM beams with periodic repeating structures at multiples of a certain distance along the propagation direction. These periodic structures make it unnecessary for the transceiver antennas to be perfectly aligned and can also alleviate the hollow divergence of OAM beams. In this paper, we propose Talbot-effect-based fractal OAM generation and detection schemes using a uniform circular array (UCA) to significantly improve capacity and BER performance in unaligned OAM transmissions. We first provide a brief overview of fractal OAM. Then, we propose the fractal OAM beam generation and detection schemes. Numerical analysis and simulations verify the effectiveness of our proposed fractal OAM generation scheme and also demonstrate improved capacity and BER performance compared to normal OAM transmissions. We also analyze how the receive UCA radius and the distance between the UCAs impact the capacity and BER performances.

中文翻译：

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分形 OAM 生成和检测方案


由于不同 OAM 模式的正交波前，轨道角动量 (OAM) 携带的电磁波具有提高光学和射频通信频谱效率的潜力。然而，OAM光束是涡旋中空且发散的，这显着降低了OAM传输的容量。此外，OAM 传输中未对齐的收发器可能会导致较高的误码率 (BER)。塔尔博特效应是一种自成像现象，可用于生成光学或射频 OAM 光束，该光束具有沿传播方向一定距离的倍数周期性重复结构。这些周期性结构使得收发器天线无需完美对准，并且还可以减轻OAM波束的空心发散。在本文中，我们提出了基于塔尔博特效应的分形 OAM 生成和检测方案，使用均匀圆形阵列 (UCA) 来显着提高未对齐 OAM 传输中的容量和 BER 性能。我们首先简要概述分形 OAM。然后，我们提出了分形 OAM 光束生成和检测方案。数值分析和模拟验证了我们提出的分形 OAM 生成方案的有效性，并且还证明了与正常 OAM 传输相比，容量和 BER 性能有所提高。我们还分析了接收 UCA 半径和 UCA 之间的距离如何影响容量和 BER 性能。