基于微滴腐蚀的微纳光纤Farby-Perot腔的折射率传感特性

为了实现高精度和高灵敏度的折射率测量，采用微米级氢氟酸液滴化学腐蚀的方法制作非对称的微纳光纤Fabry-Perot (FP)腔，具有波导尺寸小、损耗低、双折射率高和腔Q值高等优点。不同正交偏振方向的谐振模式对外界折射率变化具有不同的响应，沿光纤快轴方向的模式折射率灵敏度为133.8 nm/RI-unit，沿光纤慢轴方向的模式折射率灵敏度为117.1 nm/RI-unit,快慢轴方向的温度灵敏度均为11.99 pm/℃，通过光谱仪监测两束偏振光的波长差可实现温度独立的折射率测量。采用不同FP腔参数的光纤传感器进行实验研究，结果表明，光纤FP传感器腔直径越小，腐蚀占腔长比越高，其折射率灵敏度越高。

Refractive index sensing characteristics of microdroplet-etched micro-nano fiber Fabry-Perot resonator

In order to improve the measurement precision and sensitivity of refractive index, an asymmetric cross-sectional microfiber Fabry-Perot resonator is realized using an HF-acid droplet etching technique. The fabricated structure is featured with small size, low loss, large birefringence and high Q value. The guided modes along the orthogonal polarizations present different refractive index (RI) responses due to its dissimilar evanescent field fraction outside of the fiber. Our measured RI sensitivities are 133.8 nm/RI-unit and 117.1 nm/RI-unit for the modes along the fast axis and the slow axis, respectively. Simultaneously, the temperature responsivity is 11.99 pm/℃ for the two polarization modes. Thus the temperature cross sensitivity can be eliminated by monitoring the peak difference between the two polarizations, since they have the similar temperature coefficient but different RI responses. From experimental results, the sensitivity of the FP resonator becomes large when the diameter of cavity decreases and the ratio between the corrosion length and the cavity length increases.