三层平板介质光波导计算，该平板波导主要由3层均匀介质构成，中间的芯层折射率为n1，厚度为d，芯区生长在折射率为n2的衬底上，芯区上面的覆盖层折射率为n3。这里考虑的是n1大于n2大于n3。-Three-layer flat-plate dielectric waveguide, the flat waveguide is composed of three uniform media, the refractive index of the middle layer is n1, the thi