低NA大模场光纤高耦合效率模场适配器  

High Coupling Efficiency Mode Field Adapter with Low NA LMA Fiber

作　　者：熊峰 慕伟[2] 王洋 马云亮[2] 徐呈霖 张琦 张小贝 XIONG Feng;MU Wei;WANG Yang;MA Yunliang;XU Chenglin;ZHANG Qi;ZHANG Xiaobei(Key Laboratory of Specialty Fiber Optics and Optical Access Networks,School of Communication and Information Engineering,Shanghai University,Shanghai 200444,China;The 23rd Research Institute of China Electronics Technology Group Corporation,Shanghai 201900,China)

机构地区：[1]上海大学通信与信息工程学院,特种光纤与光接入网重点实验室,上海200444 [2]中国电子科技集团公司第二十三研究所,上海201900

出　　处：《光子学报》2024年第8期1-13,共13页Acta Photonica Sinica

基　　金：国家自然科学基金(Nos.62022053,62205192);111计划项目(No.D20231);上海市先进光波导智能制造与测试专业技术服务平台项目(No.19 DZ2294000);上海市科委项目(Nos.22010500100,22ZR1424800)。

摘　　要：为提高低数值孔径大模场光纤与单模光纤的耦合效率,并提高输出光束的光束质量,结合加热扩芯技术和大模场光纤拉锥技术实现二者的模场匹配。基于粒子扩散和绝热拉锥方程分别建立了热扩芯光纤和锥形大模场光纤的理论模型,并仿真了其模场分布和传输特性,优化了器件的结构及制备参数。采用数值孔径分别为0.06和0.05的商用和自制的锥形大模场光纤与无附加损耗的热扩芯光纤,制备得到两款模场适配器。分别对器件的插入损耗和光束质量因子进行了实验测试,基于数值孔径分别为0.06和0.05的大模场光纤的模场适配器的正向插入损耗分别为0.29 dB和0.23 dB,正反向损耗差值分别为0.19 dB和0.06 dB,输出光束的质量因子分别为1.26和1.15。仿真和实验结果表明,低数值孔径的大模场光纤对于高阶模式的抑制能力更强且受到纤芯偏移和角度偏移影响更小。基于数值孔径为0.05的大模场光纤的模场适配器具有更高的耦合效率和光束质量,在高功率光纤激光器中有广泛运用前景。Transverse Mode Instability(TMI)and Nonlinear Optical Effects(NLE)prevent high-power all-fiber lasers from further power scaling.Low Numerical Aperture(NA)Large Mode Area(LMA)active fibers can maintain large effective areas while suppressing the Higher-Order Modes(HOMs)and increasing the thresholds of NLE and TMI.Additionally,it is easier to match the passive component for low NA LMA fiber because its structure is simpler and consistent with the step-index fiber structure.Mode Field Adapters(MFAs)match the mode field between LMA fibers and Single-Mode Fibers(SMFs)and are crucial passive components in fiber laser systems.The insertion loss and beam quality of MFAs significantly affect the power scaling and beam quality of laser systems.This paper made MFA based on tapered low NA LMA fiber with NA=0.05 and Thermally Expanded Core(TEC)fibers,maintaining high coupling efficiency and improving the output beam quality.The impact of mode field mismatch,core offset,and angular misalignment between LMA fibers with different NAs and SMF on coupling efficiency and beam quality of MFA was studied theoretically and experimentally.First,theoretical models for TEC and tapered LMA fibers were built based on diffusion and adiabatic criterion equations.The mode field distribution and propagation characteristics of TEC and tapered LMA fibers were simulated based on the beam propagation method to optimize the device structure and preparation parameters.Second,a simulation model was created to analyze the insertion loss and beam quality degradation caused by mode field mismatch,core offset,and angular misalignment between LMA fibers with different NAs and SMFs.The simulation results show that reducing the NA of LMA fibers helps suppress HOMs and reduces the insertion loss and beam quality degradation of MFAs caused by core offset and angular misalignment.During the experimental process,the SMF was heated with an H2-O2 flame to expand the Mode Field Diameter(MFD)of SMF without causing transmission loss.The MFD of the TEC SMF under dif

关 键 词：光纤光学 模场适配器 光束质量 数值孔径 插入损耗 

分 类 号：TN253[电子电信—物理电子学]