聚合物平面光波导模分复用器的研制

It is predicted that the transmission capacity of the global optical fiber networks will need to increase by 1000 times in the next 30 years to meet the growing demand in the communication market. The existing wavelength-division multiplexing technology will soon exhaust the bandwidth of the single-mode fiber and its development will eventually fall behind the pace of the market growth. There is an urgent need to explore new technologies to boost the transmission capacities of optical fibers. One of the most promising technologies that are attracting world-wide attention is mode-division multiplexing, which is based on the principle of transmitting different channels through different modes in a few-mode fiber. This project proposes a new optical waveguide mode-division multiplexer for application in mode-division multiplexing systems. The proposed multiplexer has a new layout; it is composed of three different phase-matching devices and enables effective combination or separation of the spatial modes of a few-mode fiber. The multiplexer will be analyzed and designed by the coupled-mode theory and the supermode theory, and implemented with polymer optical waveguides. The thermo-optic effect of the polymer material will also be explored as a mechanism for optimizing the performance of the multiplexer. The project takes full advantage of the many features offered by the polymer optical waveguide technology, such as simple fabrication process, design flexibility, and low cost etc., and should lead to the production of a high-performance, low-cost mode-division multiplexer. The key members of the project have more than 10 years research experience in the development of polymer optical waveguide devices. The organizations they are associated with are equipped with the computing, fabrication, and testing facilities necessary for carrying out the project. The strong expertise together with the advanced facilities available should guarantee the delivery of the project. While the project focusses on the study of a specific device, namely the mode-division multiplexer, the principles and the technical skills developed in the project will form the basis for the future development of more sophisticated integrated optical devices.

未来三十年，全球光纤网络传输容量估计要增加一千倍才能满足市场的需求，现今的波分复用技术的发展很快就会耗尽单模光纤的带宽，开发新技术以提高光纤的传输容量已经刻不容缓，发展基于少模光纤的模分复用技术成了目前光通信领域的研究热点。本项目拟从机理分析入手，研制一款用于模分复用系统的光波导模分复用器，该复用器结合三种不同的相位匹配器件，把少模光纤的不同空间模式汇合或分离，布局新颖。计划发展耦合模理论与超模理论相结合的解析工具，用以分析、设计该器件，进而采用聚合物光波导技术来实现器件制作，并利用聚合物材料的热光效应来实现器件性能调控。本项目充分利用聚合物波导制作工艺简单、设计灵活、生产成本低等优点，有望研制成高性能、低成本的模分复用器。项目组主要成员研制聚合物波导器件已有有十余年经验，所属单位已具备必需的科研条件。本项目虽然针对模分复用器研发，但所开发的技术可为未来研制更为复杂的集成光学器件奠定基础。

基于少模光纤的模分复用技术是目前光通信领域的研究热点。模分复用器可以把少模光纤的不同空间模式汇合或分离，是模分复用通信系统的关键器件。项目针对模分复用通信系统的发展，研制高性能、低成本的聚合物光波导模分复用器。项目原来计划是研制三种不同相位匹配器件，并结合这三种器件设计一款处理三个空间模的模分复用器。由于模分复用通信的高速发展，原来的研究计划已不能满足该技術发展的需求。在过去四年，项目除了研制原来的三种相位匹配器件， 即相位匹配耦合器、光栅辅助耦合器与光栅模式转换器，也研究了Y分支波导与垂直耦合器在模分复用的应用，开创性结合水平与垂直Y分支波导，实现了三个与四个空间模的超宽带模分复用器，最近又成功研制了一款基于垂直相位匹配耦合器结构的六个空间模的宽带模分复用器。这些模分复用器都具有低串扰、高效率的特性，而且结构简单，具扩展性。此外，项目研制了超宽带光栅模式转换器，实现了超过100纳米的工作带宽。项目也详细研究了少模光纤与光波导的耦合问题，以帮助优化光波导设计，实现低损耗、低串扰的光纤对接。以上列举的都是国际领先的成果。除了无源器件，项目也研制了一款基于马赫曾德干涉仪结构的铌酸锂电光模式转换器、一款光栅与水平Y分支波导结合的聚合物热光模式开关与一款基于相位匹配耦合器机构的聚合物热光模式可选开关。这些器件具有前瞻性功能，可以应用于未来可重构模分复用系统。项目的研究目标与成果已远超过原来计划。已发表的论文包括Optics Letters， Optics Express， IEEE Photonics Technology Letters, IEEE Photonics Journal 等著名期刊论文共7篇、国际会议论文共12篇（包括两篇特邀报告），另外还有4篇期刊论文在评审中。其中一篇2014年国际会议论文获得“最佳学生论文奖”，另一篇2017年国际会议论文更获得“最佳论文奖”。项目开拓了聚合物光波导技術在模分复用光通信领域的应用，其中很多设计方案可以进一步推广、变化，开发出功能更为强大的器件，进一步推动模分复用光通信技術的发展。