How do I set a custom field source?

Date	Category
2023-12-11 15:31:59	Sources

The tidy3d.CustomFieldSource source can be used to inject a specific (E, H) field distribution on a plane, e.g. coming from another simulation. Internally, we use the equivalence principle to compute the actual source currents (all sources in FDTD have to be converted to current sources). Because of this, the custom field source will only produce reliable results if the provided fields decay by the edges of the source plane, or if they extend through the simulation boundaries, and are well-matched to those boundaries.

The example below illustrates how to define the tidy3d.CustomFieldSource using a dataset containing the E and H fields to describe a Gaussian field profile.

# Source bandwidth.
pulse = tidy3d.GaussianPulse(freq0=200e12, fwidth=20e12)

# Scalar gaussian field.
waist_radius = 2
ys, zs = np.linspace(-4, 4, 101), np.linspace(-4, 4, 101)
y_grid, z_grid = np.meshgrid(ys, zs)
scalar_gaussian = np.exp(-(y_grid**2 + z_grid**2) / waist_radius**2)

# Field dataset defining both E and H
dataset_EH = tidy3d.FieldDataset(
    Ey=tidy3d.ScalarFieldDataArray(
        scalar_gaussian[None, ..., None],
        coords={
            "x": [0],
            "y": ys,
            "z": zs,
            "f": [200e12],
        },
    ),
    Hz=tidy3d.ScalarFieldDataArray(
        scalar_gaussian[None, ..., None] / td.ETA_0,
        coords={
            "x": [0],
            "y": ys,
            "z": zs,
            "f": [200e12],
        },
    ),
)

# Source definition
custom_field_src = tidy3d.CustomFieldSource(
    source_time=pulse,
    center=(-1, 1, 0),
    size=(0, 8, 8),
    field_dataset=dataset_EH,
)

See this notebook to an example on setting up a tidy3d.CustomFieldSource source.