The strain-temperature cross-sensitivity problem easily occurs in the engineering strain monitoring of the self-sensing embedded with fiber Bragg grating (FBG) sensors. In this work, a theoretical investigation of the strain-temperature cross-sensitivity has been performed using the temperature reference grating method. To experimentally observe and theoretically verify the problem, the substrate materials, the preloading technique, and the FBG initial central wavelength were taken as main parameters. And a series of sensitivity coefficients calibration tests and temperature compensation tests have been designed and carried out. It was found that when the FBG sensors were embedded on different substrates, their coefficients of the temperature sensitivity were significantly changed. Besides, the larger the coefficients of thermal expansion (CTE) of substrates were, the higher the temperature sensitivity coefficients would be. On the other hand, the effect of the preloading technique and FBG initial wavelength was negligible on both the strain monitoring and temperature compensation. In the case of similar substrates, we did not observe any difference between temperature sensitivity coefficients of the temperature compensation FBG with one free end or two free ends. The curves of the force along with temperature were almost overlapped with minor differences (less than 1%) gained by FBG sensors and pressure sensors, which verified the accuracy of the temperature compensation method. We suggest that this work can provide efficient solutions to the strain-temperature cross-sensitivity for engineering strain monitoring with the self-sensing element embedded with FBG sensors.

光纤布里渊传感中, 本征存在的由温度和应变交叉引起的判断模糊问题, 一直是光纤分布式传感领域的研究热点。针对这一问题, 总结了四类解决方法: 铺设参考光纤、双参量矩阵方程测量、双物理效应结合及特种光纤判别。对每一类解决方法的原理、系统、传感性能及特点进行了分析, 并对各种方法进行了讨论、对比与评价。最后总结并展望了解决交叉敏感问题的研究方向。

Exploring and understanding the ocean is an important field of scientific study. Acquiring accurate and high-resolution temperature and depth profiles of the oceans over relatively short periods of time is an important basis for understanding ocean currents and other associated physical parameters. Traditional measuring instruments based on piezoelectric ceramics have a low spatial resolution and are not inherently waterproof. Meanwhile, sensing systems based on fiber Bragg grating (FBG) have the advantage of facilitating continuous measurements and allow multi-sensor distributed measurements. Therefore, in this paper, an all-fiber seawater temperature and depth-sensing array is used to obtain seawater temperature and depth profiles. In addition, by studying the encapsulation structure of the FBG sensors, this paper also solves the problem of the measurement error present in traditional FBG sensors when measuring seawater temperature. Through a theoretical analysis and seaborne test in the Yellow Sea of China, the sampling frequency of the all-fiber seawater temperature and depth profile measurement system is 1 Hz, the accuracy of the FBG sensors reaches 0.01 ℃, and the accuracy of the FBG depth sensors reaches 0.1 % of the full scale. The resulting parameters for these sensors are therefore considered to be acceptable for most survey requirements in physical oceanography.

光纤传感器固有的交叉敏感问题一直是光纤传感技术应用中亟需解决的问题。提出了一种多目标粒子群优化(MPSO)解调算法, 分别讨论了2个光纤布喇格光栅(FBG)中心波长在相同与不同的传感系统中的解调情况, 以及不同反射率对解调结果的影响。该算法不仅具备较高检测精度(温度测量精度为0.1 ℃, 应变精度为0.5 με), 而且系统结构简单、易于实现, 对FBG的材料、结构、中心波长及反射率无严格限制。

提出一种集温度、压力和流量多参数同时测量的新型光纤传感器，并对其原理和结构、工艺设计展开研究工作。采用靶式与悬臂梁结构相结合的机敏结构、薄壁压力应变筒结构等集成在同一传感器探头上，并利用四只光纤光栅使得温度、压力和流量三个参数得以同时检测。利用光纤光栅两两之间波长移动量“相差”或“相和”，使温度与流量、压力交叉敏感问题得以解决。同时开发了光纤传感器标校系统，这一系统可以较准确实现对所研发的多参量一体化传感器的测试结果进行检测和标校。

提出了一种基于预应力的超低温漂光纤光栅封装方法并进行了实验测试, 通过分析光纤光栅的应力和温度交叉作用的原理, 结合硬铝材料和石英管材料不同的膨胀系数, 在光纤光栅上施加预应力的结构来解决光纤光栅温度补偿问题; 通过设计和制作含预应力的封装结构产生负温度效应的方法, 使封装的光纤光栅实现光纤光栅中心波长超低温度漂移。实验结果表明: 在温度为20~80℃的测试范围内, 这种封装结构可实现光纤光栅0.0002nm/℃的超低温度漂移, 而且具有良好的稳定性和一致性。

设计了一种分离型光纤传感增敏结构,并联连接两个腔长相近的法布里-珀罗(F-P)腔。理论分析了此结构的增敏原理并制备了两组增敏结构。实验结果表明,增敏结构的压强灵敏度值由单F-P结构的4.85 nm/MPa提高到43.95 nm/MPa,温度灵敏度由单F-P腔的0.0675 nm/℃提高至0.40364 nm/℃,在相同温度下采用双腔结构可消除温度交叉敏感对测量结果的影响。此结构克服了集成式增敏结构的缺陷,在不影响原传感器结构的情况下提高了灵敏度,且可通过更换辅助腔来调节灵敏度,具有移植性好和交叉敏感小等优势。

把光纤布拉格光栅(FBG)的有效折射率、周期用二元函数泰勒展开,理论验证FBG温度-应变和应变-温度交叉敏感方式相同,得出热光系数和弹光系数均与有效折射率平方成正比例关系的结论;列出温度、应变测量计算方程式,并阐述了计算方法。测试温度、应变同时存在时FBG的波长,可知温度-应变和应变-温度交叉灵敏度系数分别为-1.4743×10 ^-6 nm/(℃·με)、-1.3948×10 ^-6 nm/(με·℃)。把FBG静力水准仪放置于露天阳台上监测一天内波长变化,代入方程式计算,得到较为精确的水准仪液体深度变化解。结果表明,使用温度、应变计算方程式求解,能够提高FBG的测量精度。