As we saw in the video in the previous unit, the General tab of the FDTD solver region
object is where you can set the dimension, background index, simulation time and simulation
The background index is the refractive index that is used in any regions where no structures
are explicitly specified.
The simulation time sets the maximum period of time that will be simulated.
The simulation may end sooner than this time if the fields decay very quickly and the early
shut off option in the “Advanced Options” tab is enabled.
To obtain accurate results, it is important for the simulation time to be long enough
so the fields can propagate through the simulation volume and fully decay.
For large simulation volumes or when studying systems that support strong resonances that
take a long time to decay, the maximum simulation time may need to be increased.
If the simulation time is too short, there will be artifacts in the results of frequency
domain monitors, for example, you may find artificial ripples in the transmission spectrum.
The simulation temperature setting is used if temperature-dependent index perturbation
materials are used in the simulation and otherwise will have no effect on the simulation.
The dimension of the solver region can either be 2D or 3D.
The 2D simulation takes the XY cross section of the structure at the z position of the
The orientation of the 2D simulation region can only be z-normal so the orientation of
the structure needs to be set up accordingly so that the dimension that should be considered
uniform and infinite is along the z-direction.
Under the geometry tab, the position and spans of the solver region can be specified.
Any structures or sources that are placed fully outside of the simulation region will
not be simulated.
Monitors that are located outside of the simulation region will not measure any data.
It can be important to extend structures that should be considered semi-infinite such as
substrates into the boundaries of the simulation region.