设计了一款基于光纤法布里-珀罗(F-P)干涉仪型的位移传感器。首先将单模光纤和无芯光纤拼接在一起, 把无芯光纤的末端切成平面, 然后把该结构固定在精密位移平台上, 最后在无芯光纤末端位置处垂直放置一面全反镜, 构成一个复合的F-P干涉仪。实验中, 调节精密位移平台上的千分尺来改变无芯光纤与平面镜镜面的距离, 从而改变F-P干涉仪的腔长。实验结果表明, 干涉仪的反射谱谐振峰中心波长随位移变化发生线性漂移, 通过考察中心波长漂移量实现位移量的精确测量。实验获得传感器最大位移灵敏度为-80.95 pm/μm, 测量最大位移量为160 μm。设计的光纤位移传感器结构简单, 易制作及灵敏度高, 在航空航天、海底探测等精度要求较高的微位移测量场合具有一定的应用前景。

A multimode interference refractive index (RI) sensor based on the coreless fiber was numerically and experimentally demonstrated. Two identical single mode fibers (SMF) are spliced at both ends of a section of the coreless fiber which can be considered as the equivalent weakly guiding multimode fiber (MMF) with a step-index profile when the surrounding refractive index (SRI) is lower than that of the coreless fiber. Thus, it becomes the conventional single-mode multimode single-mode (SMS) fiber structure but with a larger core size. The output spectra will shift along with the changes in the SRI owing to the direct exposure of the coreless fiber. The output spectra under different SRIs were numerically studied, as well as the sensitivities with different lengths and diameters of the coreless fiber. The predication and calculation showed the good agreement with the experimental results. The proposed RI sensor proved to be feasible by verification experiments, and the relative error was merely 0.1% which occupied preferable sensing performance and practicability.

针对非弱导条件下单模多模单模（SMS）结构光纤段的理论分析，研究了简单准确的数值模拟方法。利用输入场的泰勒级数展开和多模光纤内电磁场的矢量模式展开，分析了在非弱导条件下SMS结构光纤的多模光纤段中所有模式的传播特性和透射率。基于对模式特征方程的分析，通过合理选择对SMS结构光纤的多模干涉特性有贡献的最少的模式数，计算出每个模式的透射率并与实验结果比较，证明了在单模光纤和多模光纤纤芯精确对准的情况下，利用线偏振径向函数即零阶贝赛尔函数展开多模光纤内的电磁场（标量模型）可以得到很好的数值模拟结果。该结论可有效降低理论研究的复杂性。