通过全矢量有限差分法数值模拟,设计了一种大模面积平顶模场光子晶体光纤。光纤截面上空气孔为三角形格子分布,中心七个空气孔缺失并在其中心引入一低折射率区域。分析了内纤芯大小、空气孔间距和空气孔相对大小等参数变化对内纤芯折射率、基模模面积等特性的影响。给出了工艺上简单易行的平顶模场光子晶体光纤结构,其平顶模面积可达2000 μm2。发现增加内纤芯尺寸和导光波长,降低空气孔相对尺寸,可以减少光纤中的高阶模含量。

A novel design approach of realizing flattened mode large mode area photonic crystal fibers (PCFs) is presented by introducing a depressed-index region in the core of 7-rod core triangular PCFs. The influences from structural parameters,such as the size of depressed inner core,air hole pitch and the relative size of air hole,on the refractive index of inner core and the fundamental mode area are calculated with full-vectorial finite-difference method. A flattened mode PCF with mode area as large as 2000 μm2 is given,which can be easily fabricated with present technique. In the simulation,it is also found that less higher order modes will be contained in the fiber by scaling the depressed inner core and light wavelength as well as decreasing the relative size of air hole.