This video is taken from the FDTD Learning Track on Ansys Innovation Courses.
- PC Micro Cavity Tutorial (example which demonstrates a similar photonic crystal cavity)
- Monitors - Refractive index (details including definitions of each of the properties of the index monitor)
This file contains a photonic crystal cavity resonator which is a slab with higher refractive
index than the surrounding medium.
The cavity is formed by etching a pattern of holes around the center of the cavity.
Symmetry is used in the simulation region in the x and y directions to reduce the memory
For photonic crystal structures the periodicity of the structure can be important so it is
important to make sure that the shape of each meshed hole is the same in each period of
the patterning, so using an index monitor can be helpful to confirm that the mesh is
set up with the correct mesh step size to achieve this.
Add a refractive index monitor from the monitors drop down menu.
Edit the monitor using the edit button or “E” keyboard shortcut.
For the index monitor, since the number of frequency points recorded is 1 by default,
you can see that the override global monitor settings is overridden by default.
Using 1 frequency point here is fine since the structure that we are simulating is a
dielectric material which means that the refractive index doesn’t change as a function of frequency.
In the geometry tab, the monitor type is 2D Z-normal which means we’ll get the refractive
index in the XY plane at particular z position.
Set the size of the index monitor to match the size of the simulation region which is
2.5 microns in the x and y directions and the z position to slice is 0 which corresponds
to the position of the slab.
Click OK to accept the settings.
In the CAD, you can see the yellow outline of the monitor.
With the monitor selected, the available preview results are listed in the Result View window.
Right-click to view the index preview – this
doesn’t support the automatic unfolding of the monitor data across symmetry boundaries
so you can see that we can only see one quarter of the structure.
From the colour bar scale on the right you can see that the slab has a refractive index
of 2.65 and the etched holes have a refractive index of 1 as expected.
We can also see that the shape of the etched holes in each period is the same which is
what we wanted to check.
Run the simulation, and plot the refractive index result.
does apply the unfolding across the
symmetry boundaries so that we can see the refractive index cross section.
Now that we’ve seen an example of setting up and index monitor, here are some tips for
using the monitor.
You may find that if there are many small features of the structure, there can be some
graphical artifacts in the plot, so it’s best to zoom into the plot by using the zoom
mouse mode an clicking on or selecting a region of the plot to zoom into to clearly see the
material interfaces of the structure.
Index monitors may not accurately record material properties in regions using advanced non-linear
material models or grid attributes.
You can use the "nearest mesh cell" interpolation option with the "record conformal mesh when
the possible" option to see the effective index at material interfaces due to conformal meshing.
You can only see this once the structure has been meshed after running the simulation so
you won’t see this from the index preview.
If you want to get this result without running the full simulation, you can use the “Quit
& save” button in the job manager after the meshing stage of the simulation has been
completed and the simulation is in the running stage.
The spatial interpolation options are advanced features.
We do not recommend changing these options unless directed by Lumerical staff.