# Composite Grid
EME grid made out of multiple subgrids placed in sequence along the propagation axis. This is useful for structures that have both uniform and varying sections — for example, a taper connecting two straight waveguides — and for periodic structures via the Periodicity Sweep.
Each subgrid is a uniform grid with its own name, number of cells, repetitions, and mode specification. Click Add subgrid to append a new subgrid. The last subgrid extends to the simulation edge (it has no Ends at field).
# Subgrid Name
name: Name of the subgrid. Named subgrids are referenced by the Periodicity Sweep.
Default: subgrid_1, subgrid_2, ...
# Ends At
subgrid_boundaries: Coordinate at which each subgrid ends along the propagation axis. There is one boundary fewer than the number of subgrids.
Type: floating-point number
- Unit: m, μm (default), or nm
- Constraint: boundaries must be strictly increasing and lie within the simulation domain
- Required field
# Number of Cells
num_cells: Number of cells in the subgrid.
Type: integer
- Unit: unitless
- Constraint: greater than 0
- Default: 5
# Repetitions
num_reps: Number of periodic repetitions of the subgrid. Useful for periodic structures like gratings: instead of explicitly repeating the cells, the EME solver reuses the modes and the cell interface scattering matrices.
Type: integer
- Unit: unitless
- Constraint: greater than 0
- Default: 1
# Mode Specification
mode_spec: Mode specification used by all cells of the subgrid.