Viewer¶

bf.view(stack) returns an anywidget viewer for a bf.StackDevice, for Jupyter and marimo. It shows the device in 3D and in 2D cross-sections, sets up sources and monitors, runs the simulation, and shows the fields a finished simulation recorded.

Open the viewer¶

A straight silicon waveguide in the viewer (in Jupyter or marimo, end the cell with viewer):

import fdtdx
import gdsfactory as gf
import bifrost as bf
from gdsfactory.technology import LayerLevel, LayerStack

gf.gpdk.PDK.activate()

component = gf.components.straight(length=5)  # a 5 um long, 500 nm wide waveguide with ports o1 and o2

# one 220 nm thick level on the waveguide layer; silicon core in a silica cladding
layer_stack = LayerStack(
    layers={"core": LayerLevel(layer=gf.gpdk.LAYER.WG, zmin=0.0, thickness=0.22, material="core", mesh_order=1)}
)
materials = {
    "core": fdtdx.Material(permittivity=3.48**2),
    "clad": fdtdx.Material(permittivity=1.444**2),
}

stack = bf.StackDevice.from_layer_stack(
    component, layer_stack, materials,
    background="clad",                               # fills everything the core does not
    zrange_layers=["core"],                          # the box's z range is the core's
    extend_ports=(("o1", 1.0), ("o2", 1.0)),         # 1 um straight leads out of both ports
    boundary_offset=(0, 0, 1.5, -1.5, 1.5, -1.5),    # 1.5 um of cladding in y and z
    name="stack",
)
viewer = bf.view(stack)  # the interactive 3D viewer
viewer

(Outside a notebook, a script only builds the widget. To look at one without Python, use the live demo.)

The viewer has four tabs on its left:

The 3D and 2D buttons switch the view. In 2D you pick a plane (xy, xz or yz) and move a slider through the device. The camera button saves the current view as a PNG.

Run a simulation from the viewer¶

Add a source and a monitor in the Sources / Detectors tab, choose the grid and time in Simulation, and press Run. The run happens in the Python session on a background thread, with the setup locked while it goes, and its field appears in the Result tab. To place and run the objects yourself, they are in viewer.objects, viewer.config and viewer.constraints; the copy launch code button copies a script that reproduces the setup.

Load a finished simulation¶

A result simulated in a script goes to the viewer as the last step of that script (as in the bend tutorial and Results and field monitors):

viewer = bf.view(stack)
viewer.load_result(objects, arrays, config, stack=stack)

objects, arrays and config are what fdtdx.place_objects and fdtdx.run_fdtd return, and stack is the StackDevice the result was recorded on.

The Result and Sources / Detectors tabs then list the run's sources and monitors with their names, types and planes. They are read-only, because the viewer has the objects fdtdx placed, not the calls that made them. To simulate again from the viewer, add your own sources and monitors: running replaces the listed ones.

Troubleshooting¶

• A widget shows as text such as Viewer(...), or not at all. The viewer needs a notebook that supports widgets (Jupyter with anywidget installed, or marimo). End the cell with the viewer object. In a plain script nothing is displayed.
• The viewer is blank or the 3D view does not draw. It needs WebGL. Check that the browser has hardware acceleration on, or try another browser.
• Run does nothing, or fails. A run needs a source, and a monitor to record anything; a problem with the setup is reported in the viewer. For a run you control, use the scripts in Simulation setup and ports.
• The Result tab says no result is loaded. Run from the viewer, or call viewer.load_result(...) as above.