This simulation file uses the periodicity settings to simulate a cavity formed by two
Bragg mirrors with a cavity in between.
If I zoom into the view, I can see that one period of the Bragg mirror structure is set
up here which is just a corrugation in the width of the waveguide.
When this unit cell of the wider segment followed by a narrower segment is repeated many times,
it forms a frequency selective mirror.
One unit cell is set up on either side of the central cavity.
If I edit the EME solver region and look in the EME setup tab, I can see that 5 cell group
regions have been set up where groups 1 and 5 are the input and output waveguides, groups
2 and 4 contain 1 unit cell of the Bragg mirror each, and group 3 is the central cavity.
In the periodicity settings, the number of periodic groups is set to 2, since there are
2 periodic regions.
The first periodic region is cell group 2, so the start and end groups are both set to
2, and the similarly for the second periodic region, the start and end cell groups are
set to group 4.
We can then specify the number of times that we want to repeat each periodic region.
In this case, we will have 100 periods of the Bragg mirror on either side of the cavity.
In the cell group sequence below, we can verify this.
Cell group 1 is followed by cell group 2 repeated 100 times, followed by cell group 3, followed
by cell group 4 repeated 100 times, followed by cell group 5.
The number of periods of each periodic region can also be modified in Analysis mode after
finding the modes.