包层为负折射率介质的抛物型渐变光纤色散特性分析

Dispersion Characteristics in Graded-index Fiber Formed by Core with Usual Dielectric and Cladding with Negative Refractive Index

研究了纤芯为各向同性非均匀材料,而包层为负折射率均匀介质光纤的色散特性.在纤芯满足弱渐变条件的假定下,按矢量场分析法,通过芯层与包层的介电常数比ξ和磁导率比η,讨论了导波模式色散特性对左手介质包层材料的依赖性.分析表明,ξ和η对轴对称模色散曲线的低频段影响较大,但对非轴对称模影响不大.ξ和η对导波模式的截止频率没有影响.由于该光纤中的HEm1模的截止频率都等于0,所以不存在理论上的单模区,但仍可近似实现无色散传输.

The dispersion characteristics in a graded-index fiber formed by a core with usual dielectric and a cladding with negative refractive index are studied. The influence of the permittivity ratio ξ and the permeability ratio η , between the core and the cladding,on the dispersion curves and the cut-off frequencies of the guided modes is investigated. The axisymmetric mode dispersion curves in low frequency area are influenced heavily by ξ and η, but the influence of ξ and η to the dispersion characteristics of HE and EH modes is not obvious. The values of ξ and η have no influence on the cut-off frequencies of all guided modes. The cut-off frequencies of HEml modes are 0, so there is no single-mode frequency area for this fiber. But there is a frequency area which can support non-dispersion propagation.