【摘要】 为满足B5G/6G时代对高容量、低时延和可集成无线接入系统的需求，多输入多输出（MIMO）光纤无线融合（RoF）架构被广泛使用。然而，传统的MIMO RoF架构依赖多根独立光纤传输多路信号，存在光纤资源占用高、色散损耗大、布线复杂度高等问题，不利于小型化基站部署。为解决这一问题，本团队提出了一种结构简化型MIMO RoF系统架构。该方案利用多芯空芯光纤实现两路正交偏振信号在单根光纤内同步传输，结合天线极化复用与多输入多输出（MIMO）技术有效提升传输容量并降低光纤布线复杂度，为未来低成本、轻量化微型基站部署提供了可行方案。实验中搭建了2×2偏振复用MIMO RoF系统，成功实现了24 GHz频段、8/16 Gbaud QPSK信号在4 km空芯光纤与0.2 m自由空间链路中的传输。结合先进的数字信号处理（DSP）算法，该系统最高可实现64 Gbit/s的总传输速率。实验结果验证了所提方案在传输性能与系统集成方面的双重优势，为未来的微型基站部署提供了可行的技术路径。更多还原

【Abstract】 Objective The explosive growth of data-intensive services in the Beyond 5G（B5G） and 6G era,such as ultra-high-definition video streaming,virtual/augmented reality,and internet of things applications,has imposed stringent requirements on access networks,including high capacity,low latency,and lightweight deployment.To support these demands,radio-over-fiber（RoF） systems combined with multiple-input multiple-output（MIMO） and polarization-division multiplexing（PDM） technologies are considered highly promising.However,conventional MIMO-RoF architectures depend on multiple single-mode fibers for parallel transmission,resulting in excessive fiber resource consumption,which hinders the large-scale deployment of compact base stations.Therefore,it is necessary to develop a novel RoF architecture that not only minimizes fiber resources but also enhances integration,maintains high performance,and facilitates miniaturized base station deployment.Methods To address these issues,a structure-simplified 2×2 PDM-MIMO RoF system is proposed.It utilizes a multi-core hollowcore fiber（HCF） to simultaneously transmit two orthogonal polarization signals within a single fiber.This work highlights the feasibility and effectiveness of combining multi-core multiplexing with polarization-division MIMO transmission,demonstrating an important step toward future cost-effective and scalable RoF micro-base station deployment.The schematic and experimental setup are shown in Figure 1 and Figure 2,respectively.The modulated signal is separated into two orthogonal polarization channels by a polarization beam splitter（PBS）.Meanwhile,another laser is used as the local oscillator（LO）.The LO is also divided by a polarization-maintaining optical coupler（PM-OC）,and each branch is coupled with the modulated signals via polarization-maintaining optical couplers（PM-OCs）.The two orthogonally polarized optical signals are then transmitted over two independent cores of a multicore HCF with a length of 4 km.Compared with conventional schemes requiring two separate standard single-mode fibers（SSMFs） as shown in Figure 1（a）,the proposed method consolidates the dual polarization channels into a single HCF,thereby simplifying the system structure as shown in Figure 1（b）.Results and Discussions We experimentally built a 2×2 polarization-division multiplexing（PDM）-MIMO RoF system,demonstrating a transmission of 24 GHz 8/16 Gbaud QPSK signals over a 4-km HCF link and a 0.2-m free-space wireless link.By incorporating advanced digital signal processing（DSP） algorithms,the system achieves a total data rate of up to 64 Gbit/s.The experimental results demonstrate that the proposed architecture achieves reliable performance while significantly reducing system complexity.Figure 4 presents the optical spectra of the 8 Gbaud and 16 Gbaud QPSK signals after coupling with the LO and before transmission through the HCF.The received electrical spectra captured by the oscilloscope are shown in Figure 5.For 8 Gbaud QPSK signals,clear spectra are observed at a received optical power（ROP） of—19.9 dBm in both X and Y polarizations.For 16 Gbaud signals,spectra are obtained at ROP of—14.1 dBm,although the Y-polarized channel exhibites slightly lower signal-to-noise ratio（SNR） compared to the X-polarized channel.The bit error rate（BER） curves versus ROP are plotted in Figure 6.For 8 Gbaud signals in Figure 6（a）,both polarization channels achieve BER below the 7% hard-decision FEC threshold of 3.8 × 10^-3 when ROP is—17.9 dBm,and error-free transmission is achieved at—14.9 dBm.For 16 Gbaud signals in Figure 6（b）,the X-polarized channel consistently outperforms the Y-polarized channel due to SNR imbalance.The X-polarized component maintains a BER below the15% so ft-decision FEC threshold of 1.56 × 10^-2 over the entire ROP range and realizes error-free transmission at an ROP of—7.1 dBm,whereas the Y-polarized channel achieves a BER below the same FEC threshold only when the ROP reaches—11.1 dBm.These results clearly validate that the multi-core HCF enables dual-polarization MIMO signals to be transmitted within a single fiber,significantly reducing fiber usage and system complexity while maintaining high spectral efficiency and reliable performance.Conclusions In conclusion,this paper proposes and experimentally demonstrates a structure-simplified 2×2 PDM-MIMO radioover-fiber（RoF） system tailored for micro-base station deployment.By introducing a multi-core hollow-core fiber（HCF） structure,two orthogonally polarized signals are integrated and transmitted within a single fiber,effectively reducing the system’s dependence on fiber resources while enhancing overall integration and deployment flexibility.In addition,the wireless transceiver setup employing H/V polarized horn antennas not only exploits the capacity-expansion advantage of polarization multiplexing in MIMO systems,but also ensures independent transmission of polarized signals,thereby mitigating polarization crosstalk and improving transmission reliability.Experimental results show that the system successfully transmits dual-polarization QPSK signals over a 4-km HCF link and a 0.2-m free-space wireless link at 24 GHz,achieving a maximum data rate of 64 Gbit/s.Overall,the proposed scheme is validated in terms of both transmission performance and structural optimization,providing a novel solution for constructing cost-effective and easily deployable RoF micro-base stations in ultra-dense network environments,and laying a technical foundation for future shortreach,high-speed communication systems oriented toward Cloud-RAN and edge data center integration.更多还原