面向OFDR的超宽带扫频光纤激光源动态超窄线宽机理研究

The ideal light source for long range high spatial resolution optical frequency domain reflectometry (OFDR) based distributed optical fiber sensing system is the dynamic ultra-narrow linewidth and ultra-wide bandwidth linearly frequency-swept fiber laser. Due to many inherent drawbacks presented in the existing frequency-swept sources till now, they can not be used in the high performance OFDR fiber sensing systems. And even due to the lack of an efficient dynamic linewidth measurement method and other reasons, the study on the OFDR ideal sources is still not deep enough. In this proposal, we will propose an C+L band single-longitudinal-mode ultra-wide bandwidth frequency-swept fiber laser using silica-based erbium-doped fiber (Si-EDF) and bismuth-based erbium-doped fiber (Bi-EDF) cooperatively operated flat gain amplifying medium and using a novel triple-ring-nested passive-subring-cavity to select longitudinal mode, and will introduce a unique polarimeter-based optical spectrum analysis technique to measure the laser dynamic linewidth. The work contents include the theoretical and experimental study on the flat gain amplifier theoretical model establishing, the single-longitudinal-mode ultra-wide bandwidth frequency-sweep mechanism designing, the accurate frequency-sweep dynamic linewidth behavior theoretical model establishing, the sweep signal modification and compensation mechanism exploration. On the basis of well-studied characteristics of the laser dynamic linewidth, we aim to master the operating mechanism of ultra-wide bandwidth frequency-swept fiber lasing with dynamic ultra-narrow linewidth, and obtain a frequency-swept fiber laser system with a swept range from 1530nm to 1610nm and a dynamic linewidth of <1kHz during frequency sweeping. The proposed work will provide good theoretical and technical guidance for the practical development of ideal fiber laser source for high quality OFDR sensing systems.

长距离、高空间分辨率OFDR分布式光纤传感系统的理想光源是动态超窄线宽及超宽带线性扫频光纤激光器，目前较成熟的扫频光源自身存在诸多缺陷，无法高质量满足需求，甚至因缺乏有效的动态线宽测量方法等原因，对理想光源的研究还不够深人。本项目提出一种基于Si-EDF/Bi-EDF混合平坦增益和三环嵌套式新型无源子腔的C+L波段单纵模超宽带扫频光纤激光系统设计，并引入独特的偏振法光谱分析技术进行动态线宽测量，主要围绕平坦增益放大器理论模型建立、单纵模超宽带扫频机制设计、准确的扫频动态线宽行为规律理论模型建立、扫频函数修正及相关补偿方案探究等方面开展理论和实验研究，旨在充分研究动态线宽特性基础上，掌握超宽带扫频光纤激光动态超窄线宽实现机理，并实现1530nm~1610nm动态线宽<1kHz的高质量扫频激光输出。项目的预期研究成果将为高性能OFDR传感系统理想光纤激光源的实用化开发提供理论和技术指导。

本项目针对面向OFDR的C+L波段超宽带单纵模（SLM）扫频（波长扫描）光纤激光源的动态超窄线宽机理及涉及到的关键技术开展研究。根据预期研究计划，主要完成了以下研究内容：建立了Si-EDF/Bi-EDF混合平坦增益光纤放大器理论模型和基于Si-EDF的C+L波段平坦增益光纤放大器理论模型，均实现了1530~1610nm超宽带平坦增益放大的目标；首次提出了理论结合实验的复合谐振腔滤波器研究方法，基于此研制了三环嵌套、单耦合器环/双耦合器环嵌套、双耦合器环级联（DCR-CC）、“8”字形、“回”字形等复合谐振腔超窄带光纤滤波器；研制了基于重叠高双折射光纤光栅（SI-HBFBG）和DCR-CC的15种运行模式可切换的四波长SLM超窄线宽光纤激光器；研制了基于HB-FBG的亚kHz量级超窄线宽、超高光信噪比（OSNR）、超低相对强度噪声（RIN）和正交偏振输出的0.612nm间隔双波长SLM光纤激光器；研制了基于啁啾莫尔光纤光栅（CM-FBG）的覆盖全C波段的41波长可切换SLM超窄线宽光纤激光器；研制了基于DCR-CC的C+L波段SLM超窄线宽波长扫描光纤激光器；研制了基于六重重叠光纤光栅（6-SIFBGs）的高稳定性多波长随机光纤激光器；研制了基于保偏取样光纤光栅（PM-SFBG）的可切换多波长掺铥光纤激光器；搭建和验证了基于相位噪声分析的2μm波段单频光纤激光器线宽测量系统。在完成以上研究内容过程中，共发表学术论文16篇（SCI检索期刊论文11篇、TOP论文4篇），获授权发明专利1项、申请发明专利1项，培养毕业硕士研究生2名、培养在读博士研究生2名与硕士研究生3名，参加学术会议4次。