The simulation begins by setting up the FDTD region, a rectangular volume where the field evolution is computed. The user defines its size in the x, y, and z dimensions. Crucially, boundary conditions must be assigned. For an open structure radiating into free space, perfectly matched layers (PML) are applied at the boundaries to absorb outgoing waves without spurious reflections. For periodic structures like gratings or photonic crystals, periodic or Bloch boundary conditions are more appropriate. In our example, we use PML in the vertical (z) direction and periodic boundaries laterally (x, y) to model an infinite slab.
Getting Started with Ansys Lumerical FDTD: A Step-by-Step Guide lumerical fdtd tutorial
It calculates the E and H fields at each grid point as time progresses. The simulation begins by setting up the FDTD