为实现高灵敏度的折射率测量，设计了一种基于双模干涉的光纤折射率传感器，该传感器为单模多模单模光纤(SMS)结构，其中单模光纤和多模光纤具有相同的直径和纤芯折射率。剥去多模光纤的包层，将其置于待测环境中，多模光纤中激发出的两个模式之间会发生干涉，当待测环境折射率发生变化时，干涉谱中的波谷会发生移动，可根据光谱中波谷的移动量来实现对折射率的测量。利用FDTD Solutions软件进行仿真模拟，得到不同折射率下的干涉谱，结果表明，位于1517.32nm的干涉谷对折射率的敏感度为1848.2nm/RIU，最小分辨率误差仅为2.74×10-5RIU。该传感器较传统光纤传感器而言，结构简单，有着高灵敏度、低分辨率误差等优点，应用前景广阔。

To achieve highsensitivity refractive index measurement, an optical fiber refractive index sensor based on doublemode interference is designed. The sensor is a singlemodemultimodesinglemode fiber (SMS) structure, in which the singlemode fiber and the multimode fiber are of the same diameter and core refractive index. To strip the cladding of the multimode fiber and place it in the environment to be measured, interference will occur between the two modes excited out of the multimode fiber. The transmission dips of the sensor will shift when the ambient refractive index changes, so the simultaneous measurement of the refractive index can be achieved by monitoring the wavelength shifts. Using FDTD Solutions software for simulation, the interference spectra at different refractive index were obtained. The results show that the sensitivity of the dip at 1517.32nm to the refractive index is 1848.2nm/RIU, and the minimum resolution error is only 2.74×10-5RIU. Compared with the traditional optical fiber sensor, the sensor processes simple structure, high sensitivity and low resolution, making it has high potential applications.