In this eSeminar we will demonstrate how CST Studio Suite® can be used in the design process of photonic components by presenting two detailed examples. An SOI ring coupler will be used as an example of the design of a photonic integrated circuit (PIC). We will divide the ring coupler into waveguide blocks and using both 3D electromagnetic simulation and a flexible schematic to speed up the simulation task, increase the flexibility and allow the design of PICs too large for electromagnetic simulation alone. In the second part of this eSeminar, we will present a general approach to obtain dispersion diagrams for photonic crystals with the eigenmode solver. As an example a 2D tridiagonal photonic crystal will be used.