少模光纤的模式耦合引起模分复用(MDM)系统传输性能劣化,是造成MDM技术难以在实际中大规模应用的主要因素之一。精确测量少模光纤模式耦合系数和量化分析模式耦合与系统性能之间的关系,可以为系统的损伤补偿提供可靠依据。分析了当前少模光纤模式耦合测量方法的利弊,并基于背向瑞利散射原理建立了一种模式转换器/解复用器和光纤环形器结构的少模光纤模式耦合测量系统,通过与多输入多输出功率分析的测量结果进行对比,验证了所提系统的测量性能。实验结果表明,所提系统较好地实现了对9.8km少模光纤模式耦合分布的测量,且测量结果稳定。 The mode coupling of a few mode optical fibers causes deterioration of the transmission performance of a system of MDM, which is one of the main factors that make the MDM technology difficult to be applied on a large scale in practice. Accurately measuring the mode coupling coefficient of the mode-less optical fiber and the relationship between mode coupling and the system performance can provide a reliable basis for the system’s damage compensation. This paper analyzes the advantages and disadvantages of the current low mode fiber mode coupling measurement method, and based on the Rayleigh backscattering principle, a mode-less mode coupling measurement system with mode converter / demultiplexer and fiber circulator structure is established. Input multi-output power analysis of the measurement results were compared to verify the proposed system measurement performance. The experimental results show that the proposed system can well measure the coupling distribution of 9.8km less mode fiber and the measurement result is stable.