This video is taken from the varFDTD Learning Track on Ansys Innovation Courses.
This is the ring resonator simulation which we showed in the My First Simulation section.
We will add a mode expansion monitor to extract the S-parameters which are the complex transmission
coefficients for the power from the fundamental mode going from the input port to the drop
port which we will call S21, and from the input port to the through port which we will
call S31, as well as a monitor to return the 2D field profile of the light through the
drop port at a resonant frequency.
Since there is no equivalent port object to the ports that are used in FDTD Solutions
to extract S-parameters of a device, we can instead a mode expansion monitor since the
mode expansion monitor can return the forward and backward coefficients of light travelling
through a frequency domain field and power monitor in the selected mode of the waveguide.
Duplicate the through monitor and set the name to "in".
Change the x position of the monitor to –4.2 um to measure the input fields.
Add the mode expansion monitor from the Monitors menu.
Set the geometry to match the geometry of the “in” monitor with x position –4.2
um, y 3.6 um, and y span 2 um.
In the mode expansion tab, make sure the mode selection is set to "fundamental mode", select
"align to frequency monitor center", and in the “Monitors for expansion” section,
add 3 monitors.
Set the names to "in", "drop", and “through”, and select the corresponding monitors from
the drop down menu.
To get the S parameters as a result, edit the “Model” analysis group and add a new
result named “S”.
I have the pre-written code to get the transmission coefficients from the mode expansion monitor
for the in, through, and drop ports, calculate the S-parameters, and package the results
into a dataset called "S".
I will copy and paste the code into the analysis script tab
To get the 2D field profile at the drop port at 1.5 um, duplicate the “drop” monitor,
and edit it.
Set the name to “drop profile”, de-select “use source limits”, and set the number
of frequency points to 1.
Now set the center wavelength to 1.5 um.
In the Geometry tab set the monitor type to “2D X-normal” and the z span to 1 um.
Now, run the simulation.
After it completes, I can visualize the S result from the model group and plot S21 and
S31 as a function of frequency.
Apply the "Abs" scalar operation to see the amplitude of the transmission coefficients,
or the "Angle" operation to see the phase.
I can plot the simulated electric field profile from the “E” result from the “drop profile”
This gives the 1D field profile along y. Visualize the results expanded along z to see the 2D
field profile expanded in the z-dimension.