The available source types that can be added in a varFDTD simulation are the dipole source,
slab Gaussian, slab plane wave, total-field scattered-field, and the mode source.
These sources are similar to the corresponding source types in FDTD Solutions, however varFDTD
does not have equivalents to the import source, or port object from FDTD Solutions.
The sources in varFDTD have a 1D field profile in the x or y directions depending on the
source type and injection direction, but the effective field profile of the source along
the z-direction is determined by the selected vertical slab mode.
For example, consider the slab plane wave injected in the x-direction.
The field profile along y is a uniform distribution and this is what gets injected in the simulation
with effective materials.
When the fields are expanded along z, the field profile of the injected mode has the
profile of the slab mode in the z-direction instead of a uniform field profile as you
would expect for a plane wave.
The most commonly used type of source is the mode source which is used to inject a supported
mode of the cross section of the structure.
For the mode source, the field profile expanded along z using the slab mode is a very good
approximation to the mode profile in a 3D simulation.
You can edit the mode source and select the mode to inject from the General tab, the same
way as done in FDTD Solutions.
One tip is to ensure that if you use the “user select” mode selection option, the selected
mode should have the same polarization as the slab mode, otherwise the mode will not
get injected properly.