Theoretical analysis of mode evolution in an adiabatically tapered multimode fiber by coupled local mode theory

Analyzing the mode evolution characteristics of light in a tapered multimode fiber is an important research topic for multimode fibers. In this paper, an analytical method based on coupled local mode theory is introduced, which can analyze adiabatically tapered multimode fiber with different taper parameters. Compared with traditional beam propagation methods, the coupled local mode theory can greatly improve the calculation efficiency and directly reflect the mode evolution process. Therefore, it has important application prospects in the optimal design of tapered fibers. Based on the coupled local mode theory, the multimode fibers with different taper shapes are simulated, and the optimal design of tapered fibers is carried out from the perspective of fundamental mode conservation ability. In theory, the proportion of LP01 mode in output energy can account for more than 99.9%.