bifrost

The rainbow bridge between your GDSFactory(X) pipeline and FDTD(X) simulation.

bifrost turns a gdsfactory component and its layer stack into a differentiable fdtdx simulation, and ships a 3D viewer for setting up the run and inspecting its fields. It builds on gdsfactoryx, the JAX port of gdsfactory.

Documentation: https://sephiram591.github.io/bifrost/ (with a live viewer demo)

Install

Python 3.12 to 3.14. fdtdx is a required dependency, so one command installs everything. Use a fresh environment: gdsfactoryx (installed from PyPI as a dependency) provides the gdsfactory import package, so it cannot share an environment with upstream gdsfactory.

python -m venv bifrost-env && source bifrost-env/bin/activate
pip install bifrost-photonics

The distribution is named bifrost-photonics: the name bifrost on PyPI belongs to an unrelated project (OpenStack), so do not pip install bifrost. You still import bifrost as bf. To install the latest development version from GitHub instead: pip install "bifrost-photonics @ git+https://github.com/Sephiram591/bifrost.git".

For GPU simulations also install a CUDA build of JAX (see the installation page).

Quick start

A straight silicon waveguide in the viewer (in a Jupyter or marimo cell, 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

Next: run your first simulation, a 90 degree bend from an empty file to a transmission value and a field image.