本文将等效阶跃光纤方法(ESFM)推广到多包层光纤.当已知多包层坯棒折射率分布,则利用这种方法可严格计算出该坯棒的等效阶跃光纤的等效折射率差,从而可方便地估算出该坯棒拉制出光纤的各种传输参数.文中以计算双包层椭圆光纤的截止波长为例作为部分验证.理论计算和实际测量的结果表明,除个别情况外,精度达到5%.因而,在工程上解决了为确定多包层光纤的截止波长(或拉丝半径),而必须进行重复凑试拉丝和测量的困难,大大节省了时间、精力和材料.

In this paper, an Equivalent Step-Index-Fiber Method(ESFM)has been extended to multicladding fibers. Upon defining the refractive index profile for the multicladding preform, the equivalent normalized index difference for the equivalent step-index-fiber of the preform can be exactly derived by the method so that varieties of transmission parameters for the fiber drawn from the preform would be predicted conveniently. Meanwhile, cutoff wavelengths of double-cladding elliptical fibers have been calculated as an example for part confirmation. Comparision between the theory and resuls form the experiment fibers, except individual cases, shows an accuracy of 5% in predicted cutoff wavelengths. As a result, for finally determining cutoff wavelengths or fiber-drawing radii of multicladding fibers, “trial and error” between fiber-drawing and cutoff-wavelength measuring procedures can be avoided in engineering practice, saving time, energy and material.