以多极法理论为基础,提出了一种阶梯结构的光子晶体光纤。通过改变其内四层的三个结构参量(内两层孔孔径,外两层孔孔径和孔间距),实现色散绝对值在1.1～1.8 μm 的波段内变化仅为0.05～2 ps/(km·nm)的平坦甚至超平坦的特性。在此情况下对其有效模场面积进行数值模拟,充分展示了达到色散平坦和超平坦时,相对于传统光子晶体光纤,此种结构的光纤对芯区内光场的局域能力有很大程度的增强,其有效模场面积可仅为传统光子晶体光纤的1/30。最后,经过大量的数值计算和理论分析,归纳出若要此种阶梯结构的光纤在1.1~1.8 μm的波段内达到色散平坦甚至超平坦特性的设计依据。

Based on the multi-pole method, a kind of step-structure photonic crystal fiber (PCF) is put forward. It has achieved flattened and ultra-flattened dispersion within the wave band of 1.1～1.8 μm by altering three structural parameters of the inner four rings (the diameter of the two inner rings holes, the diameter of the two outer rings holes, and the pitch), the absolute value of dispersion coefficient merely changing from 0.05～2 ps/(km·nm). Moreover, the effective mode-field area also has been stimulated, which is only 1/30 of that of conventional PCFs, showing that the PCFs with flattened and ultra-flattened dispersion do well in confining the light field compared with conventional PCFs. With numerical calculation and theoretic analysis, the design basis of this kind of step-structure PCF to achieve flattend and ultra-flattend dispersion within the wave band of 1.1～1.8 μm is concluded.