Crosstalk reduction#
This example reproduces Figure 3 from []` in which the crosstalk between adjacent waveguides is suppressed.
Show code cell source
from collections import OrderedDict
import matplotlib.pyplot as plt
import numpy as np
from shapely.geometry import Polygon, box
from skfem import Basis, ElementTriP0
from skfem.io import from_meshio
from femwell.maxwell.waveguide import compute_modes
from femwell.mesh import mesh_from_OrderedDict
w_sim = 4
h_clad = 1
h_box = 1
w_core_1 = 0.5
w_core_2 = 0.5
gap = 0.5
h_core = 0.22
w_core_c = 0.2
num_c = 2
wavelength = 1.55
references = ("3a.csv", "3b.csv")
for num_c, reference in zip([1, 2], references):
reference_data = np.loadtxt(reference, unpack=True, delimiter=",")
w_core_cs = np.linspace(np.min(reference_data[0]), np.max(reference_data[0]), 15) * 1e-3
coupling_lengths = []
for w_core_c in w_core_cs:
def core_c_pos(i):
return (
-gap / 2 + (gap - w_core_c * num_c) * (i + 1) / (num_c + 1) + (i + 0.5) * w_core_c
)
polygons = OrderedDict(
core_1=Polygon(
[
(-w_core_1 - gap / 2, 0),
(-w_core_1 - gap / 2, h_core),
(-gap / 2, h_core),
(-gap / 2, 0),
]
),
core_2=Polygon(
[
(w_core_2 + gap / 2, 0),
(w_core_2 + gap / 2, h_core),
(gap / 2, h_core),
(gap / 2, 0),
]
),
**{
f"core_c_{i}": Polygon(
[
(core_c_pos(i) - w_core_c / 2, 0),
(core_c_pos(i) - w_core_c / 2, h_core),
(core_c_pos(i) + w_core_c / 2, h_core),
(core_c_pos(i) + w_core_c / 2, 0),
]
)
for i in range(num_c)
},
clad=Polygon(
[(-w_sim / 2, 0), (-w_sim / 2, h_clad), (w_sim / 2, h_clad), (w_sim / 2, 0)]
),
box=Polygon(
[(-w_sim / 2, 0), (-w_sim / 2, -h_box), (w_sim / 2, -h_box), (w_sim / 2, 0)]
),
)
resolutions = dict(
core_1={"resolution": 0.02, "distance": 0.3, "SizeMax": 0.1},
core_2={"resolution": 0.02, "distance": 0.3, "SizeMax": 0.1},
**{
f"core_c_{i}": {"resolution": 0.01, "distance": 0.3, "SizeMax": 0.1}
for i in range(num_c)
},
)
mesh = from_meshio(
mesh_from_OrderedDict(
polygons, resolutions, filename="mesh.msh", default_resolution_max=0.4
)
)
# mesh.draw().show()
basis0 = Basis(mesh, ElementTriP0(), intorder=5)
epsilon = basis0.zeros() + 3.4777**2
epsilon[basis0.get_dofs(elements=("box"))] = 1.444**2
epsilon[basis0.get_dofs(elements=("clad"))] = 1**2
# basis0.plot(epsilon, colorbar=True).show()
modes_both = compute_modes(
basis0, epsilon, wavelength=wavelength, num_modes=2, order=2
).sorted(lambda x: -x.n_eff)
# modes_both[0].show("E", direction="x")
# modes_both[1].show("E", direction="x")
coupling_length = wavelength / (2 * np.real(modes_both[0].n_eff - modes_both[1].n_eff))
# print(f"Maximum power transfer after {coupling_length} um prop length")
coupling_lengths.append(coupling_length)
plt.xlabel("Width / μm")
plt.ylabel("Coupling length / μm")
plt.plot(*reference_data, label="Reference")
plt.plot(w_core_cs * 1e3, coupling_lengths, "ro", label="Calculated")
plt.legend()
plt.show()
