基于双芯光纤耦合器的高纯度涡旋光产生研究

Design of high purity vortex generator based on dual-core fiber coupler

为了实现全光纤化轨道角动量(orbital angular momentum,OAM)模式产生系统,设计了一种基于标准单模光纤和环芯光纤的双芯光纤耦合器结构。基于模式匹配法和相位匹配原理,仿真计算了双芯光纤耦合区中轨道角动量模式光场及相位的变化。结果表明:当单模光纤中的光场耦合到环芯光纤时,会在环芯光纤中激发出多种高阶矢量模式,引起模间串扰和降低产生的轨道角动量模式纯度,同时耦合产生的轨道角动量模式能量会在具有相反拓扑电荷数的同阶模式间震荡。通过调控波导间距,对耦合效应的强弱进行调控,实现了高纯度的一阶轨道角动量模式的产生,最大耦合效率可达99%,模间串扰<−20 dB。

Based on a standard single-mode fiber(SMF)and a ring-core fiber(RCF),a dual-core fiber coupler structure is designed for the all-fiber orbital angular momentum(OAM)mode beam generation system.The evolution of the OAM mode’s field and phase distribution in the coupling region of the dual-core fiber coupler was numerically simulated.The results showed that when the optical field in the single-mode fiber is coupled to the ring-core fiber,multiple higher-order vector modes are excited in the ring-core fiber,causing inter-mode crosstalk and reducing the purity of the resulting orbital angular momentum modes.At the same time,the power of the OAM mode generated by the coupling effect oscillates between modes of the same order with opposite topological charge numbers.Finally,the strength of the coupling effect is regulated by modulating the separation distance between the waveguides,and the first-order OAM mode is generated with high purity.The maximum coupling efficiency is up to 99%,and the inter-mode crosstalk is less than−20 dB.