近年来模分复用技术被广泛认为是突破传统单模光纤通信系统和网络容量“瓶颈”的有效途径，其典型方案包括强耦合和弱耦合两种。在弱耦合模分复用方案中，模式串扰应尽量被抑制，使得各模式中的信号可独立传输和接收。文章首先对强耦合和弱耦合模式技术原理进行了介绍，之后设计制作了一种弱耦合双环型纤芯结构少模光纤，设计制作了基于模式选择耦合器的模式复用/解复用器，在此基础上演示了6模式、10 km弱耦合模分复用传输实验，仅采用强度调制和无数字信号处理的直接检测设计了一种简并模式解复用方案，并基于熔融拉锥工艺制作了该器件，最终首次实现了模分复用实时视频传输，这表明模分复用技术向实际应用迈进了重要一步。

In recent years, Mode Division Multiplexing (MDM) techniques have been widely considered as an effective approach to break out the capacity bottleneck of conventional single-mode optical-fiber communication systems and networks. The typical schemes include strongly-coupled and weakly-coupled ones. In a weakly-coupled MDM scheme, the modal crosstalk should be suppressed as much as possible. Therefore, a signal in each mode can be transmitted and received independently. In this paper, we first introduce the technical principles of strongly-coupled and weakly-coupled schemes. Then a weakly-coupled Few-Mode Fiber (FMF) with double-ring core structure, together with the mode Multiplexer (MUX) and Demultiplexer (DEMUX) based on mode-selective coupler, are designed and fabricated. Next, transmission experimental demonstration based on 6-mode 10-km weakly-coupled MDM is achieved with intensity modulation and Digital-Signal-Processing-free (DSP-free) direct detection. A degenerate mode demultiplexing scheme is designed, which is then fabricated based on the heating and tapering method. Finally, the first real-time video MDM transmission is realized, which indicates that a big step has been made for the MDM technique towards practical implementation.