This video is taken from the EME Learning Track on Ansys Innovation Courses.
The "Override periodicity" setting in the EME Analysis window allows you to set the
periodicity the same way as done in the EME setup tab.
To review, the periodic group definition table from the EME solver region's EME setup tab lets you
set up the structure with one unit cell, and then specify the number of times to repeat
the unit cell.
This is efficient since for a repeated device you only need to find the modes once for one
period of the device and the same modes can be used for repeated unit cells.
For more details, you can review the Solver Region section of the course.
Here we have a Fiber Bragg grating which can act as a wavelength selective filter, and
the wavelength is set so that we're operating in the stop band where light is reflected
from the device.
This device is more effective at reflecting light as more periods are added, so we expect
to see the transmission decrease as more periods are used.
The simulation is in Analysis mode so the Finding modes step has already been completed
with 1 period of the device.
I'll click the "Override periodicity" checkbox to enable the tool, and first try simulating
The absolute value of S21 squared will give the fraction of power transmitted to the output
mode of port 2 which is still about 100%.
Next, I'll re-run the propagation with 500 periods.
Now the transmission is about 91%.
Finally, I'll try 1000 periods, and as expected the transmission is even lower at about 79%.
Recall that index and profile monitor results do not reconstruct the results in the periodic
region correctly, but advantage is that the time it takes to get the results using the
periodicity settings is much faster than modifying the structure to include the actual number
of periods of the device.