中文说明：计算光纤模场分布和传播常数，输入模式的阶数，计算得到各类模式的模场分布。直接运行main，在其中修改参数，至少可以计算5层光纤结构。
English Description：
The mode field distribution and propagation constant of optical fiber are calculated, and the order of input mode is calculated. By running main directly and modifying the parameters, at least 5 layers of fiber structure can be calculated.