基于循环模式转换的少模光纤链路差分模式群时延管理及应用

With the growing global data traffic exponentially, the transmission capacity of standard single-mode fiber (SSMF) is fast approaching its nonlinear Shannon limit. As a new promising capacity enhancement technique, mode division multiplexing (MDM) can establish distinguishable information channels within a single core that supports a suitably restricted number of modes. However, there still occur several challenges to be addressed before practical MDM implementation. One important problem is the cumulated differential mode group delay （DMGD）arising in few-mode fiber (FMF) link. The DMGD brings arrival time difference of various modes at the receiver, leading to the degradation of transmission performance and limitation of transmission reach. Here, we propose a DMGD management scheme based on cyclic mode convertor (CMC) and investigate the design of such CMC for the MDM transmission using three spatial modes. First, we design, fabricate and characterize on-chip silicon CMC, whose operation wavelength can cover the whole C-band with mode crosstalk of less than -15dB. Consequently, by using several CMCs within a FMF link, all data streams experience the same optical path, and we are able to reduce and eliminate the different transmission delay among the guided modes. Meanwhile, we investigate an effective DMGD measurement scheme with high precision. By putting forward an analytical model to evaluate the performance of MDM transmission with DMGD management and a new MIMO equalization with capability of low complexity and high efficiency, we finally demonstrate a three-span three-mode fiber optics transmission with no less than 1Tb/s capacity and 100km FMF reach per span.

在全球数据流量爆发式增长的背景下,作为突破传统单模光纤非线性香农传输极限的新型复用扩容技术,模分复用通过挖掘空间模式自由度可以成倍提升光纤通信系统容量，但少模光纤链路存在的差分模式群时延（DMGD）使得不同模式信号到达接收机的时间存在延迟，严重限制传输系统的性能。本项目创新性提出利用循环模式转换技术进行少模光纤链路DMGD的管理，通过研制硅基片上循环模式转换器实现模式间的循环转换，器件工作波长覆盖C波段且模式转换串扰小于-15dB，最终在接收端减小甚至消除各路信号的时延差异。同时提出高效在线监测技术对少模光纤链路累积DMGD进行高精度测量，构建DMGD对模分复用传输系统影响的数学模型，优化少模光纤链路的DMGD管理，配合低复杂度、高性能的MIMO数字信号处理技术，最终验证三跨段三模复用光传输系统，每跨段少模光纤长度不低于100km，总容量不低于1Tb/s。

在全球数据流量爆发式增长的背景下,作为突破传统单模光纤非线性香农传输极限的新型复用扩容技术,模分复用通过挖掘空间模式自由度可以成倍提升光纤通信系统容量，但少模光纤链路存在的差分模式群时延（DMGD）使得不同模式信号到达接收机的时间存在延迟，严重限制传输系统的性能。本项目提出利用循环模式转换技术进行少模光纤链路DMGD的管理，通过研制硅基片上循环模式转换器实现模式间的循环转换，器件工作波长覆盖C波段且模式转换串扰小于-15dB，最终在接收端减小甚至消除各路信号的时延差异。同时提出高效在线监测技术对少模光纤链路累积DMGD进行高精度测量，构建DMGD对模分复用传输系统影响的数学模型，优化少模光纤链路的DMGD管理，配合低复杂度、高性能的MIMO数字信号处理技术，最终验证三跨段三模复用光传输系统，每跨段少模光纤长度不低于100km，总容量不低于1Tb/s。根据自然科学基金研究成果，累计发表SCI检索论文23篇，含国际知名光通信会议OFC发表论文3篇。培养博士3人，硕士6人，项目构建了光纤飞秒激光微加工器件制备和熔融拉椎光纤器件两个制备平台，光子灯笼制备器件已经在长飞光纤光缆股份公司进行产业化，循环模式转换少模光纤通信系统理论和传输损伤模型通华为公司开展了应用推广研究。