How do I import a structure from a GDSII file?

Date	Category
2023-12-06 19:13:06	Structures

In Tidy3D, complex structures can be imported from GDSII files via the third-party gdstk package, which you can install running pip install gdstk. To load the geometry from a GDSII file, you should select the cell with the geometry you want. It is usually easier to verify that we can find the correct one by name first, for example:

# Load a GDSII library from the file.
lib_loaded = gdstk.read_gds(gds_path)

# Create a cell dictionary with all the cells in the file.
all_cells = {c.name: c for c in lib_loaded.cells}
print("Cell names: " + ", ".join(all_cells.keys()))

Then you can construct Tidy3D geometries from the GDS cell just loaded, along with other information such as the axis, sidewall angle, and bounds of the “slab” using tidy3d.Geometry.from_gds(). When loading GDS cell as the cross section of the device, we can tune reference_plane to set the cross-section to lie at bottom, middle, or top of the generated geometry with respect to the axis. E.g. if axis=1, bottom refers to the negative side of the y-axis, and top refers to the positive side of the y-axis. Additionally, we can optionally dilate or erode the cross section by setting dilation. A negative dilation corresponds to erosion. Note, we have to keep track of the gds_layer and gds_dtype used to define the GDS cell earlier, so we can load the right components.

wg_height = 0.22
dilation = 0.02

geo = tidy3d.Geometry.from_gds(
    gds_cell=all_cells["TOP"],
    gds_layer=0,
    gds_dtype=0,
    axis=2,
    slab_bounds=(-0.11, 0.11),
    reference_plane="bottom",
)

You can find more details on importing GDSII files in these notebooks: Importing GDS files; Defining self-intersecting polygons.