空芯光子带隙光纤光栅腔增强气体传感技术研究

At present, gas sensing technology based on the hollow-core photonic bandgap fiber has been widely studied. But in generally the fibers used in these studies are several meters or even tens of meters long, which are not conducive to the real-time measurement and the compactness of the systems. In order to solve these problems effectively, this project will study on the cavity-enhanced photothermal gas detection method based on the hollow-core photonic bandgap fiber grating, that is, by fabricating a pair of fiber Bragg gratings in the hollow photonic bandgap fiber to form a shorter gas reflection cavity (tens of centimeters), thus a cavity enhancement effect was formed when the light was reflected several times between these two FBGs, and then using photothermal gas detection method to carry out high-precision fiber gas sensing research. The specific research as follows: (1)Study on the characteristics of FBG in the hollow fiber photonic bandgap fiber theoretically by using the FTDT analysis software; (2)Design and build a system device for the preparation of FBG by laser double beam interference method; (3) The process of preparing FBG in hollow core photonic band gap fiber by laser double beam interference exposure is studied. A low loss gas chamber with high reflection cavity is constructed; (4)Study on the sensing performance of the gas sensing system with a cavity-enhanced photonic bandgap fiber grating. The project has potential applications in the design and integration of high-sensitivity gas sensors.

目前基于空芯光子带隙光纤的气体传感所需光纤长度一般长达数米甚至几十米，不利于测量的实时性和系统的紧凑性。为有效解决上述问题，本项目拟研究基于空芯光子带隙光纤光栅的腔增强光热光谱气体探测方法，即通过在空芯光子带隙光纤中制备一对布拉格光栅构成长度较短的气体反射腔（几十厘米），使得光在两个FBG之间经过来回多次反射后形成腔增强效应，然后采用光热光谱气体探测方法开展高精度光纤气体传感技术的研究。具体研究包括：(1)采用时域有限差分法软件进行结构建模，理论研究在空芯光子带隙光纤纤芯中写制FBG后的光学特性；（2）实验搭建激光双光束干涉法制备FBG的系统装置；（3）实验研究激光双光束干涉曝光方式在空芯光子带隙光纤中制备FBG的工艺，构建具有高反射腔的低损耗气室；（4）实验研究空芯光子带隙光纤光栅腔增强结构的气体传感性能。该项目工作在高灵敏度气体传感器的设计和集成方面具有潜在的应用价值。

空芯光子带隙光纤（HC-PBF）在气体传感应用中具有重要优势，它可以使得光和被测气体在纤芯中直接相互作用，而不是常规光纤传感中利用光纤倏逝场间接作用。尽管HC-PBF的空气芯可以增强光和气体的相互作用距离，但是由于其纤芯直径一般为几个微米，使得其所需光纤较长，导致气体在空气芯中流动性受影响，器件的紧凑性也较差。如果能够在HC-PBF中写入一对光纤布拉格光栅（FBG），那么纤芯中传输的光将在两个FBG之间来回反射，在增加光和气体的相互作用距离同时可极大地减小HC-PBF的长度。基于此，本项目从FBG制备系统搭建与完善出发，通过不断实践成功搭建一套基于双光束干涉原理制备光纤光栅的系统，该方法利用一个光栅掩模就可以在普通单模光纤（SMF）制备一系列具有不同反射波长的高质量、低成本FBG。对气体传感实验所需要的装置进行初步搭建成型，并对其进行实验调试，成功地将制备的FBG引入到腔增强型气体传感技术当中，实现了氢气浓度的探测。同时，进一步开展了飞秒激光在HC-PBF中制备FBG样品的理论研究和探索性实验，明晰了空芯光子带隙光纤光栅的理论，研究了干涉光夹角与刻写布拉格光栅波长关系，积累了一定的技术经验，可为实现在HC-PBF中制备高质量FBG提供借鉴和参考。本项目研究基于空芯光子带隙光纤光栅腔增强气体传感技术，具有较强的原创性和广泛的应用前景。