用于高阶模式转换的光纤模式耦合器设计

Design of Fiber Mode Coupler for High-order Mode Conversion

光纤模式耦合器因其较宽的波长带宽、高效率的模式耦合成为全光纤超短脉冲涡旋光束产生的首选。首先研究了单模光纤、少模光纤以及空心光纤的矢量模式特性,并分别设计了用于掺镱光纤激光器的单模-少模光纤(SMF-FMF)模式耦合器和单模-空心光纤(SMF-HCF)模式耦合器。然后,采用数值仿真软件研究了模式耦合器的耦合特性,分析纤芯间距与耦合效率的关系。仿真结果表明:SMF-FMF模式耦合器可以将LP01模式转化为LP11/LP21模,且耦合效率大于96%;而SMF-HCF模式耦合器可以将HE11转化为HE21/HE31模,其耦合效率超过82%。SMF-FMF模式耦合器和SMF-HCF模式耦合器的设计为掺镱锁模光纤激光器获得大拓扑荷超短脉冲涡旋光束奠定了基础。

The fiber mode coupler has become an important choice for the generation of all-fiberultra-short pulsed vortex beams due to its wide working bandwidth and high efficiency mode coupling.In this paper,we first studied the vector mode characteristics of single-mode fiber,few-mode fiber and hollow-core fiber,and designed the single-mode-few-mode fiber(SMF-FMF)mode couplers and single-mode-hollow-core fiber(SMF-HCF)mode coupler for Ytterbium-doped fiber lasers.Then,the numerical simulation software is utilized to study the coupling characteristics of the mode coupler,and analyze the relationship between the core distance and the coupling efficiency.The simulation results show that the SMF-FMF coupler can convert LP01 mode to LP11 or LP21 mode,with a coupling efficiency of over 96%.In addition,the SMF-HCF coupler can convert HE11 into HE21 or HE31 mode with a coupling efficiency of over 82%.The SMF-FMF mode coupler and SMF-HCF mode coupler lay the foundation for obtaining large topologically charged ultra-short pulsed vortex beams based on ytterbium-doped mode-locked fiber lasers.