In this paper, we experimentally demonstrate the mitigation of atmospheric turbulence effects using phase patterns that apply the inverse transmission matrix for pre-compensation in the 200-Gbit/s free-space orbital angular momentum (OAM) multiplexed optical link. In this link, two OAM channels are multiplexed, each carrying a 100-Gbit/s quadrature-phase shift keying (QPSK) signal. In the uni-directional (forward) link, a combination of two OAM modes is generated using a designed phase pattern in each of the two channels. After the two channels are multiplexed, each OAM mode will carry the combination of signals from both channels. Such beams could perform the inverse function of turbulence-induced crosstalk. We explore the link performances including crosstalk and bit error rate (BER) under 6 different turbulence realizations with a Fried parameter of 1-mm. We find the following: (a) the inter-channel crosstalk is reduced by up to 21 dB; (b) the inter-channel crosstalk is below −10 dB for the 6 turbulence realizations when the compensation is applied; (c) a BER below the FEC limit could be realized for the 6 turbulence realizations with an optical signal-to-noise ratio (OSNR) of 16.8 dB for the uni-directional link with the compensation. Moreover, the post-compensation is also investigated for the two 100-Gbit/s OAM-multiplexed backward channels in the bi-directional link. For the backward channels, the phase patterns are used to mitigate turbulence-induced crosstalk at the receiver for backward channels, and the inter-channel crosstalk is reduced by up to 16 dB.

中文翻译：

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使用具有两个 100-Gbit/s OAM 复用信道的单向和双向自由空间光链路的预信号组合减轻大气湍流效应的实验

在本文中，我们通过应用逆传输矩阵在 200-Gbit/s 自由空间轨道角动量 (OAM) 多路复用光链路中进行预补偿的相位模式，通过实验证明了大气湍流效应的缓解。在该链路中，两个 OAM 信道被复用，每个信道都承载 100-Gbit/s 正交相移键控 (QPSK) 信号。在单向（前向）链路中，两个 OAM 模式的组合是在两个通道中的每一个中使用设计的相位模式生成的。两个通道复用后，每种OAM模式都会承载来自两个通道的信号组合。这种光束可以执行湍流引起的串扰的反函数。我们探索了包括串扰和误码率 (BER) 在内的链路性能，在 6 种不同湍流实现下，弗里德参数为 1 毫米。我们发现： (a) 通道间串扰降低了 21 dB；(b) 当应用补偿时，6 种湍流实现的通道间串扰低于 -10 dB；(c) 对于具有补偿的单向链路，6 个湍流实现可以实现低于 FEC 限制的 BER，光信噪比 (OSNR) 为 16.8 dB。此外，还研究了双向链路中两个 100-Gbit/s OAM 复用后向信道的后补偿。对于后向信道，相位模式用于减轻接收器处的湍流引起的后向信道串扰，