面向环境扰动的多点复用光纤FBG超声探测机理与系统实现

Ultrasonic detection based on the fiber Bragg grating is a very important technique for nondestructive testing field. However, the FBG “operating-point drift” caused by the disturbance of the environment (such as changes of temperature and strain) is a problem that has long plagued the industry. Meanwhile, the developments of detection technology are also required to achieve the detection point as much as possible for a single fiber link. To solve these problems, we propose an ultrasonic detection method based on FBG "average effect" and the multi-wavelength laser transient response, with multi-point detection and anti-disturbance ability of the environment. Several groups of FBGs will be used both as the ultrasonic detectors and a comb filter for the multi-wavelength laser, which determine the corresponding laser wavelength of each. The FBG “average effect” for ultrasonic response will be utilized transform the ultrasonic signal into the laser transient response. At meanwhile, the polarization hole burning effect will be utilized to suppress the mode competition in the erbium-doped fiber laser and ensure the stable multi-wavelength lasing oscillation and multi-point ultrasonic detection. The "arranging in parallel" approach of FBGs will be used to eliminate the FBG operating-point drift caused by background temperature and strain changes. Meanwhile, we will also establish a dynamic physical model of multi-wavelength laser based on polarization-dependent gain. This model will be used to clarify the mechanism and kinetics of multi-wavelength laser system transient response of the ultrasound; this model will be also used to optimize sensing systems. Thus the results of the project will have both an important theoretical significance and great usefulness for ultrasonic detection applications.

光纤FBG超声探测技术是无损检测的重要工具。然而环境扰动（如温度和应变）造成的FBG“工作点漂移”是困扰业内已久的问题。同时探测技术的发展也要求一条光纤链路上实现尽可能多的探测点。针对上述问题，我们提出了一种基于FBG“平均效应”和多波长激光瞬变响应的超声探测方法，具备多点探测和抗环境扰动的能力。多组FBG匹配光栅既被用作超声探测器，又被用作多波长激光器的梳状滤波器，决定了各自的工作激光波长。我们将利用FBG的“平均效应”将超声转化为对应激光波长的瞬变响应；同时利用偏振烧孔效应抑制掺铒光纤的模式竞争，实现多波长激光谐振，保证多路探测的实现。我们还将利用FBG匹配光栅的“平行布置”方式，消除温度、应变等环境扰动造成的工作点漂移。我们也将建立基于偏振增益相关的动态激光器物理模型，阐明多波长激光瞬变响应的超声探测的动力学规律，并进行系统优化。针对超声传感，本项目的研究具有重要应用价值和学术意义。

主动超声探测技术是一项应用于结构健康监测、无损检测、材料表征和医疗诊断等领域的强有力超声监测手段。传统的主动超声探测使用的是电类的压电陶瓷换能器，这种换能器在一些特殊的应用场合，如飞机机翼的结构健康监测中，存在体积大、易损坏、易受电磁干扰等严重缺陷。而全光纤主动超声探测系统具备体积小、重量轻的优势，更适合嵌入式应用，同时其抗电磁干扰能力使得其应用场合更加广泛，为结构体提供更加高效实时的监测。本项目根据计划安排，对以下内容展开研究：偏振增益分立的多波长FRL-FUS激光建立与超声微扰响应的研究；多波长FRL-FUS超声微扰激光谐振及超声传感性能优化；多波长FRL-FUS超声探测系统谐振腔的整体设计与实现；光纤侧面多点、能量均衡超声激发的设计与实现。根据以上研究，我们实现了：1.设计工作点可切换的自适应多点光纤超声传感器，通过调节可调谐光纤激光器，实现了5激光通道的可切换操作，它解决了在掺铒光纤激光器中不易实现多点超声探测的问题；2. 建立基于波长相干增益的掺铒光纤激光器动态模型，为FRL-FUS激光系统的性能优化及多波长掺铒光纤激光器的设计和优化提供较高的指导意义；3. 设计出利用可调谐FBG滤波器实现多点可切换的光纤超声传感器，实现了8条探测通道下的灵活切换；4. 提出并实现了一种基于偏振相关损耗调制的多波长掺铒光纤激光器，并建立了该多波长掺铒光纤激光器的物理模型；5.建立了基于偏振烧孔效应的多波长FRL-FUS理论模型，设计了相应的超声传感器；6. 设计光纤侧面激发多点、能量均衡的超声换能器。这种多点超声激发技术与FRL-FUS系统相结合，将为实现全光纤超声收、发一体化的主动超声探测系统提供指导意义。