How to use the automatic nonuniform meshing? What steps per wavelength will be sufficient?

Date	Category
2023-12-04 18:58:43	Grid Specification

By default, Tidy3D configures the GridSpec object to having AutoGrid, which is an advanced meshing algorithm to automatically define a nonuniform grid in all three domain directions. The resolution of this grid is specified using the desired minimum steps per wavelength in each material (min_steps_per_wvl = 10 by default). This specification, therefore, requires a target wavelength, which can be provided directly to grid_spec or inferred from any sources present in the simulation. Detailed examples on how to set up AutoGrid are present on this notebook.

As a gold rule of thumb, the default value of 10 grid points per wavelength should be a good starting value for min_steps_per_wvl. However, other application-specific features must be considered when defining the appropriate simulation mesh, such as very thin geometries or large electric field gradients, as can usually occur, for example, in the presence of resonances, highly confined fields, or at metal-dielectric interfaces. Additional control over the mesh is obtained by the dl_min parameter, which imposes a lower bound of the grid size regardless of the structures present in the simulation, including override structures with enforced=True. This is, however, a soft bound, meaning that the actual minimal grid size might be slightly smaller. Finally, the max_scale sets the maximum ratio between two consecutive grid steps. Different grid configurations can be chosen for each direction, as illustrated below:

grid_spec = td.GridSpec(
grid_x=td.AutoGrid(min_steps_per_wvl=20,dl_min=0.01),
grid_y=td.AutoGrid(min_steps_per_wvl=15),
grid_z=td.AutoGrid(min_steps_per_wvl=10,max_scale=1.6),
wavelength=1.0,
)