How can i give the refractive index or dielectric constant of a sample on the line defect ( Where I will delete rods , it will be the plain path for light) which we are creating on the photonic crystal rod in air configuration in comsol. I believe that rod in air configuration rod having one refractive index and then to air.But when i want to give a refractive index of sample.. I m in doubt how can i give this value in comsol ?