水分子对长周期光纤光栅波长变化的影响机理研究

After studied and improved of the existing theoretical model, the liquid water molecules diffusion-reaction model of silica fiber is established to solve the resonant wavelength drift problem of underwater LPFG. In theory, the diffusion equation of liquid water molecule in the silica optical fiber is used for the theoretical analysis and numerical calculation. The rules of diffusion of water molecules in the cylindrical optical fiber and the resulting LPFG wavelength change mechanism were studied. On the experiment, the AFM is used to monitor the diffusion process and the degree of infiltration of water molecules in the fiber. The change rule of synchronous observation LPFG resonant wavelength resonance wavelength drift is observed by the spectrometer to verify the liquid water molecule in the silica optical fiber diffusion-reaction model and the diffusion mechanism and provide the powerful support for theoretical calculation. Finally, using the diffusion equation of liquid water molecule in the silica optical fiber and the resonance wavelength variation formula of LPFG, the quantitative function between diffusion rate and LPFG resonant wavelength variation is proposed, which can provide a theoretical guidance for the elimination of the influence of underwater LPFG wavelength drift. The research results of this project would have significant academic value and guiding significance for LPFG sensors and fiber optic sensors in the underwater environment and other engineering applications.

针对当前LPFG谐振波长水下漂移的问题，本项目通过对已有理论模型的研究和修正，建立液态水分子对石英光纤的扩散-反应模型。在理论上，利用液态水分子在石英光纤中的扩散方程进行理论分析和数值计算，研究水分子在圆柱型光纤中的扩散规律和由此导致的LPFG波长变化机理。在实验上，利用AFM监测水分子在光纤中的扩散过程和渗入程度，并利用光谱仪同步观测LPFG谐振波长的变化规律和谐振波长漂移量，据此验证液态水分子在石英光纤中的扩散-反应模型和扩散机理的正确性，并为理论计算提供了强有力的实验支持。最后利用液态水分子在石英光纤中的扩散方程和LPFG谐振波长变化量公式，得到水分子扩散系数、扩散速率与LPFG谐振波长变化量之间的定量关系，为消除LPFG波长水下漂移影响提供理论指导。该研究成果对LPFG及光纤类传感器在水下工程中的应用都具有重要的学术价值和指导意义。

针对光纤光栅类型的传感器波长水下漂移的问题，本项目通过对已有理论模型的研究和修正，提出液态水分子对石英光纤的扩散-反应模型。在理论上，利用液态水分子在石英光纤中的扩散方程进行理论分析，并利用软件仿真计算了水分子渗入对LPG波长偏移的影响。在实验上，利用SEM扫描电镜观察了浸水前后光纤表面形貌变化，发现显著的膨胀现象，直观的证明了水分子对光纤材料的侵蚀作用；并利用光谱仪观测LPG水中（60℃，360小时）谐振波长的变化规律和谐振波长漂移量，据此验证了液态水分子在石英光纤中的扩散-反应模型和扩散机理的正确性。该研究成果对LPG及光纤类传感器在水下工程中的应用都具有重要的学术价值和指导意义。