在5G/6G光载无线接入网中，远端无线单元需具备多波束赋形功能，以支持泛在移动终端的可靠接入。针对这一需求，多芯光纤凭借其通道数量多、通道间时延一致性好的优势，成为具有潜力的链路方案。提出一种基于多芯光纤的远端光真时延多波束赋形架构，可用于5G光载无线接入网。该架构利用多芯光纤作为链路，并在中心单元部署具有等色散间隔的啁啾光栅用于提供等间距时延。通过分别调节多路光载波的波长，系统可连续调整远端对应波束的指向，实现中心化的多波束操控。为了验证架构可行性，采用2 km的7芯光纤作为光载无线链路开展实验，搭建了2×2远端波束赋形验证系统。实验结果表明：通过调谐各个光载波的波长，可实现各波束指向的独立控制；与传统单模光纤相比，多芯光纤将通道间时延抖动降低了1个量级以上，最大时延抖动仅为1.7 ps，从而确保波束指向的长期稳定性。此外，实验还表明，多芯光纤的芯间串扰对预设时延和宽带无线信号信噪比的影响可忽略不计。本架构为实现远端波束赋形功能提供了可行、稳定的解决方案，对于5G/6G移动接入网具有重要应用价值。
In 5G/6G radio-over-fiber (RoF) networks, remote radio units (RUs) require multi-beamforming functionality to ensure reliable access for ubiquitous mobile terminals. To meet this requirement, multi-core fibers (MCFs) have emerged as a promising solution for RoF links due to their advantages of supporting multiple channels and maintaining excellent inter-channel delay consistency. Here, we proposes a remote optical true-time-delay multi-beamforming architecture based on MCFs, which is suitable for 5G RoF networks. The architecture utilizes MCFs as the link, while deploying chirped fiber Bragg gratings with equal dispersion spacing to provide equal-space time delays at the centralized unit. By independently tuning the wavelengths of each optical carriers, the corresponding beam direction can be continuously adjusted, enabling centralized multi-beam control. To validate the feasibility of this architecture, we use a 2-km 7-core fiber as the RoF link for experiment and build a 2×2 remote beamforming system. Experimental results demonstrate that by tuning the wavelength of each optical carrier, independent control of each beam direction can be achieved. Compared to single-mode fibers, MCF reduces inter-channel delay jitter by more than an order of magnitude, with a maximum delay jitter of 1.7 ps, ensuring long-term stability of the beam direction. Furthermore, the inter-core crosstalk of MCF has a negligible impact on both the preset delays and the signal-to-noise ratio of broadband wireless signals. This architecture provides a feasible and stable solution for realizing remote beamforming, offering significant application value for 5G/6G mobile access networks.
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