A refractive index sensor based on a multi-core micro/nano fiber is proposed for low refractive index solutions. At first, the mode field distribution of the tapered multi-core fiber is analyzed with the finite element model (FEM). After that, the relationship between the refractive index sensitivity and the diameter of the multi-core micro/nano fiber is calculated. At last, four sensors with different sizes are explored, and when the taper length is 16.20 mm, the refractive index sensitivity of the sensor can reach 5815.50 nm/RIU, which agrees with the theoretical analysis. The refractive index measurement error is less than 0.5‰, which has a high practical application value. The longer the taper length is, the smaller the fiber diameter is. According to the theoretical analysis, when the fiber diameter is less than 4.864 µm, the structure sensor’s refractive index sensitivity is higher than 10000 nm/RIU. At the same time, when the sensor’s taper length is 15.99 mm, its temperature sensitivity is −0.1084 nm/°C. Compared with single-mode fiber, the sensor proposed here has the advantages of stability, compact structure, and high sensitivity, which has a potential in the field of seawater salinity measurement.

中文翻译：

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基于多芯微纳米纤维的新型高灵敏度折射率传感器

提出了一种基于多芯微纳米纤维的折射率传感器，用于低折射率解决方案。首先，利用有限元模型（FEM）分析了锥形多芯光纤的模场分布。此后，计算折射率灵敏度与多芯微/纳米纤维的直径之间的关系。最后，研究了四种不同尺寸的传感器，当锥度长度为16.20 mm时，传感器的折射率灵敏度可以达到581.50 nm / RIU，与理论分析相符。折射率测量误差小于0.5‰，具有较高的实际应用价值。锥度长度越长，纤维直径越小。根据理论分析，当纤维直径小于4.864 µm时，结构传感器的折射率灵敏度高于10000 nm / RIU。同时，当传感器的锥度长度为15.99 mm时，其温度灵敏度为−0.1084 nm /°C。与单模光纤相比，这里提出的传感器具有稳定性强，结构紧凑，灵敏度高的优点，在海水盐度测量领域具有潜力。