The Brillouin sensing technology in multimode optical fibers has received much attention due to its ability to simultaneously transmit multiple parameters, such as temperature and strain, and its higher information capacity and transmission efficiency. Additionally, lithium niobate possesses excellent electro-optical properties, so it shows potential application value in the sensing field and is expected to provide higher sensitivity and precision. Owing to the maturity of manufacturing processes, current research on fiber optic sensing focuses on silicon-based materials, however, there are fewer studies of fibers in which lithium niobate is used as the core material, thereby underestimating its application potential. In this work, the Brillouin scattering effects in lithium niobate optical fibers are investigated numerically. We simulate the intra-mode backward Brillouin scattering characteristics of the first five orders of LP modes in micrometer-sized lithium niobate fibers by means of finite-element simulation to explore its intrinsic law.

First of all, the relationship between the Brillouin frequency shift and gain for the first five optical mode interactions is analyzed in detail. The results show that in the case of intra-mode backward stimulated Brillouin scattering, the peak of Brillouin frequency shift exhibits a significant redshift ranging from 20.63 GHz to 18.747 GHz. The Brillouin gain coefficient decreases from 13.503 m^–1·W^–1 to 4.0115 m^–1·W^–1 with the increase of mode order, in which mode LP₀₁ having the strongest gain intra modal interaction means the best sensing sensitivity. In addition, compared with ordinary silica fiber, the lithium niobate fiber has Brillouin gain increased by about 5 orders of magnitude, which means that fibers with lithium niobate as the core can have higher sensing sensitivity. In addition, it is found that although there are significant differences in the Brillouin frequency shift values of each optical mode under intra modal interactions, the sound velocity of their corresponding acoustic modes is always consistent under the same acoustic mode. In data processing, it is noticed that this is because as the mode order changes, the corresponding effective refractive index decreases to ensure that each acoustic mode of the material always has the same sound velocity. These findings provide a foundation for further studying the lithium niobate fiber sensors with electro-optic properties.