【摘要】 随着全球数据流量的爆发式增长，传统单模光纤的通信容量已逼近香农极限，面临“容量危机”。少模光纤通信技术作为一种突破性解决方案，利用多个空间模式的正交性进行模式分集复用，可以显著提升光纤通信系统的传输容量，同时保持与传统单模光纤良好兼容和较低的能耗。本文综述了少模光纤通信系统中的关键器件和技术，包括自由空间型、全光纤型和光波导型三种模分复用/解复用器，弱耦合和强耦合两种类型少模光纤及其损伤测量技术，少模掺铒光纤放大器和少模拉曼光纤放大器两种放大器，接收端数字信号处理技术和近年来少模光纤通信系统的代表性实验进展，并探讨了未来少模光纤通信的研究方向。更多还原

【Abstract】 Significance As the cornerstone of the modern information society, optical fiber communications serve as critical infrastructures supporting the development of next-generation information technologies such as the Internet, 5G communications, big data, cloud computing, and artificial intelligence. It has been designated as a strategically prioritized industry in China. However, with global data traffic growing exponentially, the transmission capacity of traditional singlemode fiber is rapidly approaching the Shannon limit, and the “capacity crisis” has become a major challenge restricting the development of future communications. Against this backdrop, the development of revolutionary new optical fiber communication technologies has become a strategic frontier fiercely contested by academia and industry worldwide. Fewmode fiber, with its unique spatial mode multiplexing characteristics, is regarded as the most promising technical pathway to break through current communication bottlenecks. Its core advantages are reflected in three key aspects: First, by utilizing multiple orthogonal spatial modes for mode-division multiplexing, it can significantly enhance the transmission capacity of a single fiber. Second, compared to alternative solutions like multi-core fiber, few-mode fiber achieves capacity expansion solely by increasing the number of transmission modes, giving it a distinct advantage in energy efficiency. Most importantly, it maintains strong compatibility with existing single-mode fiber infrastructure, ensuring relatively low deployment complexity. Due to the strengths, few-mode fiber technology is considered a key enabler for 6G communications, widely recognized as the most industrially viable solution for achieving ultra-high-capacity transmission at Pbit/s or even Ebit/s scales.Progress This paper reviews the research progress on mode multiplexers/demultiplexers, few-mode fibers, few-mode fiber amplifiers, and the unique equalization techniques specific to few-mode fiber communication systems. First, the advancements in mode division multiplexing/demultiplexing devices are introduced. The devices are primarily categorized into three types: free-space mode multiplexers/demultiplexers(Figure 4), all-fiber mode multiplexers/demultiplexers(Figure 8), and optical waveguide-based mode multiplexers/demultiplexers(Table 1). The working principles and performance parameters of each type are discussed in detail. Next, the types of few-mode fibers and their impairment measurement techniques are reviewed. The parameter characteristics and application scenarios of different few-mode fibers are presented, along with the measurement methods and performance evaluations of impairments unique to few-mode fibers(Table 2). Subsequently, the mechanisms and optimization approaches of few-mode erbium-doped fiber amplifiers and few-mode Raman fiber amplifiers are elaborated, focusing on aspects such as gain coefficients and differential mode gain. Finally, the multiple-input multiple-output(MIMO) equalization methods for few-mode fiber communication systems are summarized, including data-aided equalization methods and blind equalization methods without data assistance(Figures 34 and 36), along with some representative transmission experiments in few-mode fiber communication systems.Conclusions and Prospects Few-mode fiber communication systems, as a crucial development direction for nextgeneration optical communication technologies, have attracted extensive attention from both academia and industry due to the significant potential in enhancing communication capacity. This review provides a detailed discussion on the research progress of key technologies in few-mode fiber communication systems. Although substantial advancements have been achieved in the key technologies, numerous challenges remain for their practical implementation. With continuous breakthroughs in core technologies and improvements in system integration capabilities, few-mode fiber communication systems are expected to achieve more efficient, stable, and cost-effective optical transmission in the future, which will provide strong support for meeting the ever-growing global demand for communication capacity.更多还原