Theoretical study of mode evolution properties in a 3×1 adiabatic tapered single-mode fiber combiner

摘要

We study the mode evolution properties in a 3×1 adiabatic tapered single-mode fiber combiner (ATSMFC) in theory. The fabrication of the combiner for single mode fibers based on adiabatic tapered fused bundle (TFB) technique with the assistant of low index glass capillary is introduced. The whole taper region can be seen as three phase: single-mode fibers, multi-core fiber and multi-mode fiber. Supermodes of three-core fiber with scalar mode results are derived based on coupling mode theory. The analysis is verified with numerical examples by a fully vectorial finite element mode solver (Comsol Multiphysics). Simulation results show that the three input core modes in single-mode fibers gradually evolve into three supermodes in three-core fiber and then evolve into three low-order modes in the multi-core fiber. Effective indices for different modes are calculated which can depict the evolution process vividly. The results may be useful for practical high power fiber laser systems.