面向传感应用的气体和液体填充空心布拉格光纤研究

In this project, we focus our attention on the basic issues concerning the gas- and liquid-filled hollow core Bragg fibers (HC-BFs) for trace-gas detection and liquid refractive index measurement. Firstly, the regulatory mechanisms of structural parameters of the multilayered cladding on the photonic bandgap characteristics and the influencing factors on the transmission properties of guided-wave modes for the gas- and liquid-filled HC-BFs are investigated systematically to provide the HC-BF-based platforms for trace-gas detection and liquid refractive index measurement. Secondly, the characteristics of broadband and low-loss transmission are used to satisfy the requriments of long-distance propagation for mid-infrared (mid-IR) laser light and to act as a long-path cell for multicomponent trace-gas with high sensitivity. Meanwhile, by investigating the resonant directional coupling mechanism among different HC-BF cores and its influencing factors, an optimized design for the directional coupler with broadband mid-IR operation range will be proposed for meeting the requirement of multichannel detecion of multicomponent trace-gas. Thirdly, based on the coupling interaction between the core-guided mode and the defect mode localized in the cladding, the relationship between the wavelength shifts of the defect mode and the changes of the refractive index in fiber core is explored as the novel liquid-filled HC-BF-based sensing mechanism for the measurement of liquid refractive index, which is expected to overcome the conflict between the high sensitivity and large dynamic range in the current wavelenth-modulation scheme for core-guided mode. We believe that the research in this project will be helpful and valuable for building a miniaturized and compact HC-BF-based on-line system for detecting the gaseous and liquid matter composition with high sensitivity.

本项目瞄准气体和液体填充空心布拉格光纤（HC-BF）在痕量气体检测和液体折射率测量应用方面的基本问题，首先研究包层结构对气体和液体填充HC-BF光子带隙特性的调控作用和导波模式传输特性的影响因素，为建立基于HC-BF的痕量气体检测和液体折射率测量平台奠定基础；结合HC-BF的宽带低损耗传输特性，研究利用不同HC-BF纤芯间导波模的谐振耦合效应实现光波定向耦合，旨在解决构建高灵敏度痕量气体多组分、远程、多路光纤检测系统中关于中红外探测光宽带低损耗传输介质和光纤定向耦合器的关键技术问题；基于包层缺陷模与纤芯导波模的相互耦合作用，研究利用液体填充HC-BF的缺陷模谐振波长偏移与纤芯折射率变化的关系作为传感新机理，旨在克服当前纤芯导波模谐振波长调制方案中高灵敏度和大动态范围不能兼顾的矛盾。本项目研究结果对于构建基于HC-BF的小型化、高灵敏度气态和液态物质成分光纤在线检测系统将具有重要的参考价值。

由于具有新颖独特的导波机制，基于一维光子带隙（PBG）效应的空心布拉格光纤（HCBF）表现出灵活方便的带隙调控能力和优良的宽带低损耗传输特性。尤其是，大芯径HCBF中空纤芯易于填充气体和液体，为光与物质相互作用提供了良好平台，极其适合痕量气体检测和生化传感应用。本项目针对当前物质成分光纤在线检测技术中存在的突出问题，重点围绕气体和液体填充HCBF在气体检测和生化传感中的应用需求，相继开展了适用于构建中红外痕量气体多组分、远程检测系统和高灵敏度、小型化荧光光谱检测系统，以及兼具高灵敏度和大动态范围的液体折射率传感器的HCBF及器件的结构设计与传输特性研究。. 通过系统研究气体和液体填充HCBF的PBG结构和导波模式特性，阐明了基于二元结构周期和三元结构周期的HCBF中的导波模式特性差异，提出了满足中红外痕量气体检测和液体折射率测量应用需求的低损耗传输HCBF优化设计方案；首次提出将HCBF应用于荧光光谱检测，通过研究利用常规空心布拉格光纤（CHCBF）的光子带隙效应和含缺陷层空心布拉格光纤（DHCBF）的横向谐振效应作为剩余激发光滤波机制，提出了基于CHCBF和DHCBF的小型化荧光光谱检测方案；研究了利用液体填充具有低折射率差包层DHCBF中的谐振波长作为特征波长，通过优化缺陷层结构参数，可以有效地改善特征波长与纤芯折射率之间的线性关系，在此基础上提出了兼顾高灵敏度和大动态范围的液体折射率测量方案；对基于高折射率差包层HCBF中一阶和二阶带隙结构和导波模式特性差异进行了比较研究，并对基于一阶和二阶带隙的折射率传感性能及其影响因素进行了对比分析，结果表明高阶带隙更适合用于较高折射率液体测量。. 本项目所得研究成果对于丰富和发展基于HCBF的气态和液态物质成分光纤在线检测技术具有参考价值和指导意义。