基于螺旋微结构光纤光栅的高阶OAM产生技术及机理研究

High-order orbital angular momentum (OAM) beams could greatly increase the capacity and rate of the communication networks. The spatial OAM generators would introduce the large coupling loss and poor compatibility. Currently, all-fiber high-order OAM generators (>2th-order) are in the theoretical stage, and the coupling mechanism is still unclear. In this project, we intend to carry out the research on the generation and mechanism of the high-order orbital angular momentum mode based on the helical micro-structured fiber gratings (HMFG), study the relationship between the cross-section symmetry of micro-structured optical fiber and the OAM mode order. The research contents include: design and build the HMFG fabrication system by means of hydrogen-oxygen flame; design and fabricate the N-fold HMFG; generate and test the high-order OAM based on N-fold HMFG. We experimentally demonstrated the HMFG fabrication method by means of hydrogen-oxygen flame, and optimized (increased) the fiber cross-symmetry by selectively inflating the air holes of the micro-structured optical fiber. Finally, we expect to obtain the all-fiber high-purity (>99%) and high-order ( ≥6th-order) OAM generators, providing key technical support for high-speed all-fiber communication networks based on OAM modular division multiplexing.

高阶轨道角动量（OAM）光束可以极大地提高全光通信网络的容量和速率。空间型OAM产生器和全光纤通信网络的耦合损耗大、兼容性差。目前全光纤型高阶（>2阶）OAM产生技术的研究大多处于理论阶段，耦合机理仍不明晰。本项目拟研究基于螺旋微结构光纤光栅（HMFG）的高阶OAM产生技术及物理机理，主要研究微结构光纤横截面对称性与产生OAM阶数的关系。研究内容包括：氢氧焰加热法制备HMFG系统的设计和搭建；横截面N重对称的HMFG的设计和制备；基于N重对称HMFG的高阶OAM的产生及测试。本项目提出了利用氢氧焰加热法制备螺旋微结构光纤光栅的技术，并利用选择性膨胀微结构光纤空气孔的方法优化（增加）光纤横截面对称性，目的是研制出全光纤型高纯度（>99%）高阶（≥ 6阶）OAM产生器件，为实现OAM模分复用的高速全光通信网络提供关键技术支持。

基于螺旋光纤光栅（Helical fiber grating，HFG）的高阶OAM产生器可有效提高通信容量，然而国内外目前还处于理论仿真阶段。本项目主要研究基于N重对称的螺旋微结构光纤光栅（HMFG）的高阶轨道角动量（OAM）的产生技术及物理机理，建立完善的HMFG理论分析模型，并实验研究微结构光纤横截面对称性对产生的OAM模式阶数的影响，研制出高纯度的高阶OAM产生器件。基于此，本项目搭建了基于氢氧焰、CO2激光和飞秒激光的HMFG制备系统，可用于制备各种周期和各种类型的HMFG；实现了基于光子晶体光纤、少模光纤、椭圆芯光纤等微结构光纤光栅的制备；搭建了反射和透射集成的复合OAM测试系统，实现了不同周期微结构光纤光栅OAM模式的检测；集成空间光调制器、起偏器和玻片等元器件，实现OAM模式的纯度和偏振特性测试。.本项目已发表期刊论文12篇，申请发明专利3项，授权实用新型2项；培养博士生1人，硕士生4人，博士后1人，项目组成员参加国内学术会议8次。