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fix grating coupler simulation #539

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fix grating coupler simulation #539

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9 changes: 2 additions & 7 deletions gplugins/tidy3d/get_simulation_grating_coupler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,6 @@
from gdsfactory.technology import DerivedLayer, LayerStack, LogicalLayer
from gdsfactory.typings import CrossSectionSpec, LayerSpecs

from gplugins.common.base_models.component import move_polar_rad_copy
from gplugins.tidy3d.materials import get_medium


Expand Down Expand Up @@ -427,11 +426,7 @@ def get_simulation_grating_coupler(
+ box_thickness
)
waveguide_port_size = [size_x, size_y, size_z]

xy_shifted = move_polar_rad_copy(
np.array(port.dcenter), angle=np.deg2rad(angle), length=port_waveguide_offset
)
waveguide_port_center = [xy_shifted[0], xy_shifted[1], (size_z) / 2]
waveguide_port_center = [-sim_size[0] / 2 + port_waveguide_offset, 0, 0]

waveguide_monitor = td.ModeMonitor(
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@bzhangflex bzhangflex Mar 27, 2025

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The main issue I found while testing this was that the mode monitor z span was too large. The mode monitor was extending into the si substrate, which caused the monitor to overlap for slab modes instead of waveguide modes. I would recommend setting the default values (eg zmargin=0) so that the monitor doesn't extend into the substrate.

center=waveguide_port_center,
Expand Down Expand Up @@ -466,7 +461,7 @@ def get_simulation_grating_coupler(

# Define Gaussian beam source
gaussian_beam = td.GaussianBeam(
size=(td.inf, td.inf, 0),
size=(fiber_mfd, td.inf, 0),
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@bzhangflex bzhangflex Mar 27, 2025

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The source size is a bit small, I would recommend using at least 2x fiber_mfd, 3x would be even better.

center=[fiber_port_x, 0, fiber_z],
source_time=td.GaussianPulse(freq0=freq0, fwidth=fwidth),
angle_theta=np.deg2rad(-fiber_angle_deg),
Expand Down
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