【摘要】 基于少模光纤的模分复用技术可使传输容量增加数倍,是目前光纤通信系统的研究热点.当复用模式数量较多时,模式之间的串扰可在接收端采用多输入多输出数字信号处理算法解决.差分模式群时延（DMGD,DMGD）越大,算法复杂度越高,为了降低接收机的复杂度需要使用低DMGD的少模光纤.本文提出了使用变分法分析任意芯层折射率高于包层的少模光纤,推导出了这类光纤中基模的模斑尺寸、各个模式归一化传播常数、相对于基模的DMGD的解析表达式,以及它们与归一化频率和光纤制造参数的关系.在此基础上,以梯度型少模光纤为研究对象,优化了光纤参数,得到能够传输前6个LP模,在C和L波段|τ_DMGD|<15 ps/km的少模光纤的优化参数为:最大芯层折射率与包层折射率之差n₁-n₂=0.01,纤芯半径a=14μm,折射率分布指数α=1.975.最后讨论了光纤制造误差对DMGD的影响.更多还原

【Abstract】 Mode-division multiplexing（MDM） technology based on few-mode fibers（FMFs） is the current research hotspot of optical fiber communication system because of its ability to increase the transmission capacity several times.When the number of multiplexed modes is large,the crosstalk between modes can be removed by multiple input multiple output digital signal processing algorithm at the receiving end.The larger the differential mode group delay（DMGD,TDMGD）,the more complex the algorithm is.Therefore,in order to reduce the complexity of the receiver,it is necessary to use FMFs with low DMGD.The variational method is proposed to analyze any FMFs with higher refractive index of core than that of cladding.The analytical formula of the fundamental mode size,the normalized propagation constant for each of all guided modes,and DMGD relative to the fundamental mode are derived.Moreover,their relationship with the normalized frequency and other fiber manufacturing parameters are given.On this basis,the graded-index FMFs are studied,and the fiber parameters are optimized.The optimization parameters are the difference between the maximum core refractive index and cladding refractive index n₁-n₂=0.01,the core radius a=14 μm,and the paramenter of refractive index distribution α=1.975.In the optimized FMF,6 LP modes can be guided and|T_DMGD| is less than 15 ps/km within the C band and L band.In the end,the effects of the fiber manufacturing errors on DMGD are discussed.更多还原