用fdtd方法 模拟集成光学离子交换中扩散离子浓度的分布 进而求得折射率的分布。更创新性加入了 可变扩散系数 条件（绝对原创）-FDTD method using ion-exchange integrated optics simulation of the spread of the distribution of ion concentration to obtain the distribution of refractive index. More innovative and joi