I have a problem to design a Photonic crystal structure.



I have a question, I want to design a Photonic crystal structure and I face to a problem.
what is ‘index’ and ‘material’ in this picture? and what is difference between them?



"Index" specifies only the real part of the refractive index of your object. It defines the material as a simple dielectric that has no loss and the refractive index is frequency independent.

"Material" is using material data from the material database and it would be typically a dispersive model that has both real and imaginary part of the refractive index that is frequency dependent. You can later review the material data and fit by going to Main toolbar -> Check -> Material Explorer:

Note that the “Index” is used when material is set to “Object defined dielectric”. If you use any other material, the index value is ignored and given material data is used instead(e.g. Silicon).