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光纤的截止波长是光纤设计的重要参量之一。利用全矢量正交函数模型对空气孔辅助光纤的模式截止特性进行了讨论。分析表明 :由于光纤包层中存在空气孔 ,即使不考虑材料色散 ,包层的有效折射率也与波长有关 ;包层有效折射率由包层中空气孔的大小和波长决定 ,与芯子的掺杂浓度无关。在所研究的波长范围之内 ,与传统的W型光纤类似 ,在包层中空气孔的相对尺寸d/Λ较大时出现了基模截止现象。d/Λ从 0 .2到 0 .9变化时 ,光纤的各阶模式的截止波长都随之减小 ;各阶模式的截止波长随d/Λ变化曲线的斜率随模式阶次的升高而降低。
The cut-off wavelength of optical fiber is one of the most important parameters in optical fiber design. The mode-cutoff characteristics of air-hole assistant fiber are discussed using the full-vector orthogonal function model. The analysis shows that due to the existence of air holes in the fiber cladding, the effective refractive index of the cladding is related to the wavelength even without considering the material dispersion. The effective refractive index of the cladding is determined by the size and wavelength of the air holes in the cladding, Doping concentration has nothing to do. Within the wavelength range studied, similar to the conventional W-type fiber, the fundamental mode cutoff occurs when the relative size of the air holes in the cladding is large, d / Λ. When d / Λ varies from 0.2 to 0.9, the cut-off wavelength of each mode of optical fiber decreases. The slope of cut-off wavelength of each mode varies with the order of d / Λ reduce.