The solver region is where we can set the size of the simulation region, simulation
time, background index, boundary conditions, mesh, and the settings for the effective index
Most of the settings in the solver region are the same as for the FDTD solver region,
except for the settings in the “Effective index” tab.
We won’t cover the settings from the other tabs in detail here, but you can review them
either from the Solver Region section of the FDTD 100 course, or from the Knowledge Base
page linked below.
The Effective index tab includes settings used to calculate the effective 2D materials,
which allow the 3D structure to be represented as a 2D simulation.
This includes the slab mode position, effective index calculation method and associated options,
simulation bandwidth, test mode locations, and the slab mode polarization selection.
As we discussed in the Solver Physics section, you first need to select the slab mode by
setting the slab mode x and y position.
The solver will use the slab material profile along z at that location and calculate the
supported modes of the given profile.
The slab mode position is indicated in the view port by a green cross.
The position needs to be placed so that that z cross section includes the core material
that will be guiding the light.
The default values for the effective index calculation method and the options to optimize
the meshing in the z-direction, and clamp the effective material properties to be within
the range of refractive index values of the physical materials typically don’t need
to be changed.
The simulation bandwidth should be set to “broadband” to include the material dispersion
when simulating a broadband source wavelength range.
If the bandwidth is set to “broadband”, you can also modify the material fitting parameters
which we will discuss later.
Test points allow you to use the Material Explorer to check the calculated effective
material properties at different locations other than the slab mode position.
Only one slab mode can be selected, and you can choose to select the “E mode” which
is the fundamental TE mode with electric field polarized in the XY plane, or the “H mode”
which is the fundamental TM mode with electric field polarized along z, or use the “user
select” option to select a higher order slab mode profile.
If you have a device which supports one TE mode and one TM mode, you will need to run
2 simulations with different slab modes in each simulation to characterize the response
of both the TE and TM mode.
The selected slab mode profile is plotted below.
In the next unit, we’ll go over some simulation region setup tips.