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。

为满足未来不断发展的接入网络业务需求，提出了一种基于自零差检测的高速模式复用无源光网络方案。在该方案中，少模光纤中的一个空间模式传送信号载波(即导频)，其他空间模式用于传输信号。在接收端，导频和信号通过模式解复用器分离，导频作为接收端的本振与信号进行混频，实现自零差检测。借助于低串扰的少模光纤和模式复用/解复用器，接收端无需多入多出技术处理，即可实现导频与信号低串扰的分离。相比于偏振复用的自零差检测，基于模式复用的自零差检测可以有效地提高频谱效率。自零差检测可以有效地抑制激光器相位噪声，大大降低光线路终端或光网络单元对激光器线宽的要求。在接收端，由于不需要额外的本振，信号处理无需进行频偏的补偿，对载波相位恢复的要求也大大降低，从而有效降低了接收端数字信号处理的复杂度。利用该方案实验实现了4×40 Gbit/s 偏振复用正交频分复用信号经过55 km两模式少模光纤和模式复用解复用器后的无误码自零差检测。与背对背传输相比，55 km少模光纤引入的Q因子代价小于1 dB。

Space-division multiplexing (SDM) using multi-core fibers (MCFs) and few-mode fibers (FMFs) was proposed as a solution to increase capacity and/or reduce the cost per bit of fiber-optic transmission. Advances in passive and active SDM devices as well as digital signal processing have led to impressive SDM transmission demonstrations in the laboratory. Although the perceived advantages in terms of capacity and cost per bit that SDM offers over parallel SMF bundles are not universally accepted, SDM is beginning to emerge as an indispensable solution in major network segments. The introduction of the spatial degree of freedom allows optical networks to overcome fundamental limitations such as fiber nonlinearity as well practical limitations such as power delivery. We describe these application scenarios that the optical communications industry has already began to explore. From a fundamental science point of view, concepts such as the principal modes, generalized Stokes space, and multi-component solitons discovered in SDM research will likely have a broad impact in other areas of science and engineering.

设计了一种基于MEMS技术的可调谐光学滤波器, 它通过光栅将输入的宽带光信号色散展开, 以一个MEMS扭镜选择将对应滤波器通带的光信号反射至输出端, 从而实现光学滤波和波长调谐功能。滤波器的输入端采用单模光纤, 输出端采用多模或者少模光纤, 可以实现窄带且平顶的通带特性。经过参数优化, 仿真分析得结果显示, 采用多模/少摸光纤输出的两种滤波器, 其0.5 dB和25 dB带宽分别为0.95 nm/0.29 nm和1.39 nm/0.69 nm, 分别满足100 GHz和50 GHz信道间隔的DWDM系统要求。由于输出端采用多模或者少摸光纤, 从该滤波器输出的光信号不能继续在单模光纤中传输, 只能由光探测器接收, 因此该滤波器一般应用于全光网络节点中的下载端口。

A few-mode fiber (FMF) is designed to support three spatial modes (LP₀₁, LP_11a, and LP_11b) and fabricated through plasma chemical vapor deposition (PCVD)and rod-in-tube (RIT) method. Using PDM-DFTS-OFDM- 32QAM modulation, wavelength division multiplexing, mode multiplexing, and coherent detection, we successfully demonstrated 200 Tb/s (375×3×178.125 Gb/s) signal over 1 km FMF using C and L bands with 25 GHz channel spacing. After 1 km FMF transmission, all the tested bit error rates (BERs) are below 20% forward error correction (FEC) threshold (2.0×10^–2). Within each sub-channel, we achieved a spectral efficiency of 21.375 bits/Hz in the C and L bands.

基于少模光纤的模分复用系统能继续提高光纤通信系统的传输容量，目前已成为全球的研究热点。在介绍了少模光纤设计后，文章对3种模式选择性激励技术(偏移注入、长周期光纤光栅和空间光调制)的激励机制、特点及实现进行了研究，并重点介绍了基于空间光调制的模式选择性激励技术。