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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1.1～1.8μm的波段内变化仅为0.05～2ps/(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1.1～1.8μm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 theory of multipole method, a step-structured photonic crystal fiber is proposed. By changing the three structural parameters of the inner four layers (inner two-layer hole diameter, outer two-layer hole diameter and hole spacing), the change of the absolute value of dispersion in the waveband of 1.1 ~ 1.8μm is only 0.05 ~ 2ps / (km. nm) flat even ultra-flat nature. In this case, the numerical simulation of the effective mode field area shows that when the dispersion is flat and ultra-flat, compared with the conventional photonic crystal fiber, the optical fiber with such a structure has a great local capability to the light field in the core region The degree of enhancement, the effective mode field area can only be 1/30 of the traditional photonic crystal fiber. Finally, after a large number of numerical calculations and theoretical analysis, the design basis for achieving the dispersion flatness and ultra-flatness characteristics of the fiber with such a ladder structure in the wavelength band of 1.1 to 1.8 μm is summarized.