The cell group definition table defines how the solver region is divided into smaller
groups and cells based on the cross sections of the device, and how the modes are solved
in each cell.
The number of groups, which corresponds to the rows in the table, is determined by the
"number of cell groups" setting.
You can add a maximum of 1000 cell groups.
Cell groups are listed in order from x min to x max.
"Group span" sets the x span of the cell group.
In this example, we have a device with three cell groups.
The first group starts at "x min" of the solver region.
The next group starts from the "x max" of the previous group.
Note that group spans can be modified in the analysis stage after finding modes, like shown
in My First Simulation section.
"Cells" sets the number of cells to use over the group span.
Cells within a cell group will have uniform x spans.
Use 1 cell in regions where the cross section is uniform since modes don't change.
When the structure cross section is smoothly varying, use multiple cells and the CVCS subcell
method to avoid staircasing effects (like mode converter example from earlier).
"Modes" sets the number of modes to solve for in all cells of the group.
Its default value is set by the "number of modes for all cell groups" unless "allow custom
eigensolver settings" is checked.
Use more modes in regions where light is travelling at steeper angles, or where the structure
can support more modes (for example, the interference region of an MMI coupler, or a free space
region) "Custom" shows whether custom eigensolver
settings are being used for finding modes.
To set custom settings, select "allow custom eigensolver settings", select the cell group
in the table and click the "custom settings for cell group x" button, where x will be
the selected cell group number.
Clear by clicking the "clear settings for cell group x" button.
We will show an example of how to set custom settings in the demo later in this section.
"Cell range" displays cell number range of each cell group (cells are numbered starting
from 1 at x min) "Start" and "stop" display range of x positions
covered by the cell group (determined by x min and the group spans)