Thermal Simulations

GDSFactory includes an FEM plugin, femwell, which allows you to run thermal simulations. You can simulate the component layout directly and account for critical effects such as metal dummy fills, ensuring more accurate thermal performance analysis.

import gdsfactory as gf
from gdsfactory.generic_tech import get_generic_pdk
from skfem.io import from_meshio

gf.config.rich_output()
PDK = get_generic_pdk()
PDK.activate()

LAYER_STACK = PDK.layer_stack

LAYER_STACK.layers["heater"].thickness = 0.13
LAYER_STACK.layers["heater"].zmin = 2.2

heater = gf.components.straight_heater_metal(length=50)
heater.plot()

s = heater.to_3d()
s.show()

Example based on femwell

from collections import OrderedDict

import matplotlib.pyplot as plt
import numpy as np
from femwell.maxwell.waveguide import compute_modes
from femwell.mesh import mesh_from_OrderedDict
from femwell.thermal import solve_thermal
from shapely.geometry import LineString, Polygon
from skfem import Basis, ElementTriP0
from tqdm import tqdm

w_sim = 8 * 2
h_clad = 2.8
h_box = 2
w_core = 0.5
h_core = 0.22
h_heater = 0.14
w_heater = 2
offset_heater = 2 + (h_core + h_heater) / 2
h_silicon = 0.5

polygons = OrderedDict(
    bottom=LineString(
        [
            (-w_sim / 2, -h_core / 2 - h_box - h_silicon),
            (w_sim / 2, -h_core / 2 - h_box - h_silicon),
        ]
    ),
    core=Polygon(
        [
            (-w_core / 2, -h_core / 2),
            (-w_core / 2, h_core / 2),
            (w_core / 2, h_core / 2),
            (w_core / 2, -h_core / 2),
        ]
    ),
    heater=Polygon(
        [
            (-w_heater / 2, -h_heater / 2 + offset_heater),
            (-w_heater / 2, h_heater / 2 + offset_heater),
            (w_heater / 2, h_heater / 2 + offset_heater),
            (w_heater / 2, -h_heater / 2 + offset_heater),
        ]
    ),
    clad=Polygon(
        [
            (-w_sim / 2, -h_core / 2),
            (-w_sim / 2, -h_core / 2 + h_clad),
            (w_sim / 2, -h_core / 2 + h_clad),
            (w_sim / 2, -h_core / 2),
        ]
    ),
    box=Polygon(
        [
            (-w_sim / 2, -h_core / 2),
            (-w_sim / 2, -h_core / 2 - h_box),
            (w_sim / 2, -h_core / 2 - h_box),
            (w_sim / 2, -h_core / 2),
        ]
    ),
    wafer=Polygon(
        [
            (-w_sim / 2, -h_core / 2 - h_box - h_silicon),
            (-w_sim / 2, -h_core / 2 - h_box),
            (w_sim / 2, -h_core / 2 - h_box),
            (w_sim / 2, -h_core / 2 - h_box - h_silicon),
        ]
    ),
)

resolutions = dict(
    core={"resolution": 0.04, "distance": 1},
    clad={"resolution": 0.6, "distance": 1},
    box={"resolution": 0.6, "distance": 1},
    heater={"resolution": 0.1, "distance": 1},
)

mesh = from_meshio(
    mesh_from_OrderedDict(polygons, resolutions, default_resolution_max=0.6)
)
mesh.draw().show()

And then we solve it!

currents = np.linspace(0.0, 7.4e-3, 10)
current_densities = currents / polygons["heater"].area
neffs = []

for current_density in tqdm(current_densities):
    basis0 = Basis(mesh, ElementTriP0(), intorder=4)
    thermal_conductivity_p0 = basis0.zeros()
    for domain, value in {
        "core": 90,
        "box": 1.38,
        "clad": 1.38,
        "heater": 28,
        "wafer": 148,
    }.items():
        thermal_conductivity_p0[basis0.get_dofs(elements=domain)] = value
    thermal_conductivity_p0 *= 1e-12  # 1e-12 -> conversion from 1/m^2 -> 1/um^2

    basis, temperature = solve_thermal(
        basis0,
        thermal_conductivity_p0,
        specific_conductivity={"heater": 2.3e6},
        current_densities={"heater": current_density},
        fixed_boundaries={"bottom": 0},
    )

    if current_density == current_densities[-1]:
        basis.plot(temperature, shading="gouraud", colorbar=True)
        plt.show()

    temperature0 = basis0.project(basis.interpolate(temperature))
    epsilon = basis0.zeros() + (1.444 + 1.00e-5 * temperature0) ** 2
    epsilon[basis0.get_dofs(elements="core")] = (
        3.4777 + 1.86e-4 * temperature0[basis0.get_dofs(elements="core")]
    ) ** 2
    # basis0.plot(epsilon, colorbar=True).show()

    modes = compute_modes(basis0, epsilon, wavelength=1.55, num_modes=1, solver="scipy")

    if current_density == current_densities[-1]:
        modes[0].show(modes[0].E.real)

    neffs.append(np.real(modes[0].n_eff))

length = 320  # um
print(f"Phase shift: {2 * np.pi / 1.55 * (neffs[-1] - neffs[0]) * length}")
plt.xlabel("Current / mA")
plt.ylabel("Effective refractive index $n_{eff}$")
plt.plot(currents * 1e3, neffs)
plt.show()

Phase shift: 3.786321638790277