Add support for 2D EME simulations

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improved error message and handling when attempting to load a non-existent task ID.
 - `ClipOperation` now fails validation if traced fields are detected.
 - Warn if more than 20 frequencies are used in EME, as this may lead to slower or more expensive simulations.
+- EME now supports 2D simulations.
 
 ## [2.8.3] - 2025-04-24
 

tests/test_components/test_eme.py

@@ -166,7 +166,7 @@ def test_eme_grid():
                     assert mode_plane.size[dim] == 0
                 else:
                     assert mode_plane.center[dim] == sim_geom.center[dim]
-                    assert mode_plane.size[dim] == sim_geom.size[dim]
+                    assert mode_plane.size[dim] == td.inf
 
     # test that boundary planes span sim and lie at cell boundaries
     for grid in grids:
@@ -296,22 +296,6 @@ def test_eme_simulation():
     _ = sim2.plot(y=0, ax=AX)
     _ = sim2.plot(z=0, ax=AX)
 
-    # must be 3D
-    with pytest.raises(pd.ValidationError):
-        _ = td.EMESimulation(
-            size=(0, 2, 2),
-            freqs=[td.C_0],
-            axis=2,
-            eme_grid_spec=td.EMEUniformGrid(num_cells=2, mode_spec=td.EMEModeSpec()),
-        )
-    with pytest.raises(pd.ValidationError):
-        _ = td.EMESimulation(
-            size=(2, 2, 0),
-            freqs=[td.C_0],
-            axis=2,
-            eme_grid_spec=td.EMEUniformGrid(num_cells=2, mode_spec=td.EMEModeSpec()),
-        )
-
     # need at least one freq
     with pytest.raises(pd.ValidationError):
         _ = sim.updated_copy(freqs=[])
@@ -422,10 +406,6 @@ def test_eme_simulation():
     with pytest.raises(pd.ValidationError):
         _ = sim.updated_copy(monitors=[monitor])
 
-    # test boundary and source validation
-    with pytest.raises(SetupError):
-        _ = sim.updated_copy(boundary_spec=td.BoundarySpec.all_sides(td.Periodic()))
-
     # test max sim size and freqs
     sim_bad = sim.updated_copy(size=(1000, 1000, 1000))
     with pytest.raises(SetupError):
@@ -1244,10 +1224,10 @@ def test_eme_sim_subsection():
     subsection = eme_sim.subsection(region=region, eme_grid_spec="identical")
     assert subsection.size[2] == 1
 
-    # 2d subsection errors
+    # 2d subsection
     region = td.Box(size=(2, 2, 0))
-    with pytest.raises(pd.ValidationError):
-        subsection = eme_sim.subsection(region=region)
+    subsection = eme_sim.subsection(region=region)
+    assert subsection.size[2] == 0
 
 
 def test_eme_periodicity():
@@ -1365,3 +1345,18 @@ def test_eme_grid_from_structures():
             names=[None, "wg", None],
             num_reps=[1, 2, 1],
         )
+
+
+def test_eme_sim_2d():
+    freq0 = td.C_0 / 1.55
+    sim_size = (3, 0, 3)
+    eme_grid_spec = td.EMEUniformGrid(num_cells=5, mode_spec=td.EMEModeSpec())
+    monitor = td.EMEFieldMonitor(size=(td.inf, td.inf, td.inf), name="field")
+    eme_sim = td.EMESimulation(
+        size=sim_size,
+        axis=2,
+        freqs=[freq0],
+        eme_grid_spec=eme_grid_spec,
+        monitors=[monitor],
+        port_offsets=(0.5, 0),
+    )

tests/test_components/test_mode.py

@@ -80,12 +80,16 @@ def get_mode_sim():
     permittivity_monitor = td.PermittivityMonitor(
         size=(1, 1, 0), center=(0, 0, 0), name="eps", freqs=FS
     )
+    boundary_spec = td.BoundarySpec(
+        x=td.Boundary.pml(), y=td.Boundary.periodic(), z=td.Boundary.pml()
+    )
     sim = td.ModeSimulation(
         size=SIZE_2D,
         freqs=FS,
         mode_spec=mode_spec,
         grid_spec=td.GridSpec.auto(wavelength=td.C_0 / FS[0]),
         monitors=[permittivity_monitor],
+        boundary_spec=boundary_spec,
     )
     return sim
 
@@ -122,12 +126,12 @@ def test_mode_sim():
         _ = sim.updated_copy(freqs=FS[0], grid_spec=grid_spec)
     # multiple freqs are ok
     _ = sim.updated_copy(grid_spec=td.GridSpec.uniform(dl=0.2), freqs=[1e10] + list(sim.freqs))
-    _ = td.ModeSimulation(
+    _ = sim.updated_copy(
         size=sim.size, freqs=list(sim.freqs) + [1e10], grid_spec=grid_spec, mode_spec=MODE_SPEC
     )
 
     # size limit
-    sim_too_large = sim.updated_copy(size=(2000, 2000, 0), plane=None)
+    sim_too_large = sim.updated_copy(size=(2000, 0, 2000), plane=None)
     with pytest.raises(SetupError):
         sim_too_large.validate_pre_upload()
 

tidy3d/components/eme/grid.py

@@ -8,7 +8,7 @@
 import numpy as np
 import pydantic.v1 as pd
 
-from ...constants import RADIAN, fp_eps
+from ...constants import RADIAN, fp_eps, inf
 from ...exceptions import SetupError, ValidationError
 from ..base import Tidy3dBaseModel, skip_if_fields_missing
 from ..geometry.base import Box
@@ -762,7 +762,7 @@ def num_cells(self) -> pd.NonNegativeInteger:
     @property
     def mode_planes(self) -> List[Box]:
         """Planes for mode solving, aligned with cell centers."""
-        size = list(self.size)
+        size = [inf, inf, inf]
         center = list(self.center)
         axis = self.axis
         size[axis] = 0

tidy3d/components/eme/simulation.py

@@ -22,9 +22,13 @@
 from ..medium import FullyAnisotropicMedium
 from ..monitor import AbstractModeMonitor, ModeSolverMonitor, Monitor, MonitorType
 from ..scene import Scene
-from ..simulation import AbstractYeeGridSimulation, Simulation
+from ..simulation import AbstractYeeGridSimulation, Simulation, validate_boundaries_for_zero_dims
 from ..types import Ax, Axis, FreqArray, Symmetry, annotate_type
-from ..validators import MIN_FREQUENCY, validate_freqs_min, validate_freqs_not_empty
+from ..validators import (
+    MIN_FREQUENCY,
+    validate_freqs_min,
+    validate_freqs_not_empty,
+)
 from ..viz import add_ax_if_none, equal_aspect
 from .grid import EMECompositeGrid, EMEExplicitGrid, EMEGrid, EMEGridSpec, EMEGridSpecType
 from .monitor import (
@@ -187,12 +191,12 @@ class EMESimulation(AbstractYeeGridSimulation):
     boundary_spec: BoundarySpec = pd.Field(
         BoundarySpec.all_sides(PECBoundary()),
         title="Boundaries",
-        description="Specification of boundary conditions along each dimension. If ``None``, "
-        "PML boundary conditions are applied on all sides. NOTE: for EME simulations, this "
-        "is required to be PECBoundary on all sides. To capture radiative effects, "
-        "move the boundary farther away from the waveguide in the tangential directions, "
-        "and increase the number of modes. The 'ModeSpec' can also be used to try "
-        "different boundary conditions.",
+        description="Specification of boundary conditions along each dimension. "
+        "By default, PEC boundary conditions are applied on all sides. "
+        "This field is for consistency with FDTD simulations; however, please note that "
+        "regardless of the 'boundary_spec', the mode solver terminates the mode plane "
+        "with PEC boundary. The 'EMEModeSpec' can be used to "
+        "apply PML layers in the mode solver.",
     )
 
     sources: Tuple[None, ...] = pd.Field(
@@ -256,16 +260,6 @@ class EMESimulation(AbstractYeeGridSimulation):
     _freqs_not_empty = validate_freqs_not_empty()
     _freqs_lower_bound = validate_freqs_min()
 
-    @pd.validator("size", always=True)
-    def _validate_fully_3d(cls, val):
-        """An EME simulation must be fully 3D."""
-        if val.count(0.0) != 0:
-            raise ValidationError(
-                "'EMESimulation' cannot have any component of 'size' equal to "
-                f"zero, given 'size={val}'."
-            )
-        return val
-
     @pd.validator("grid_spec", always=True)
     def _validate_auto_grid_wavelength(cls, val, values):
         """Handle the case where grid_spec is auto and wavelength is not provided."""
@@ -587,7 +581,6 @@ def _post_init_validators(self) -> None:
         self._validate_sweep_spec()
         self._validate_symmetry()
         self._validate_monitor_setup()
-        self._validate_sources_and_boundary()
 
     def validate_pre_upload(self) -> None:
         """Validate the fully initialized EME simulation is ok for upload to our servers."""
@@ -795,25 +788,6 @@ def _validate_monitor_setup(self):
                         "('num_reps != 1' in any 'EMEGridSpec'.)"
                     )
 
-    def _validate_sources_and_boundary(self):
-        """Disallow sources and boundary."""
-        if self.boundary_spec != BoundarySpec.all_sides(PECBoundary()):
-            raise SetupError(
-                "In an EME simulation, the 'boundary_spec' must be `PECBoundary` "
-                "on all sides (the default value). The boundary condition along "
-                "the propagation axis is always transparent; boundary conditions "
-                "in the tangential directions are imposed in 'mode_spec' in the "
-                "EME grid."
-            )
-        # commented because sources has type Tuple[None, ...]
-        # if self.sources != ():
-        #    raise SetupError(
-        #        "EME simulations do not currently support sources. "
-        #        "The simulation performs full bidirectional propagation in the "
-        #        "'port_mode' basis. After running the simulation, use "
-        #        "'smatrix_in_basis' to use another set of modes. "
-        #    )
-
     def _validate_size(self) -> None:
         """Ensures the simulation is within size limits before simulation is uploaded."""
 
@@ -1206,3 +1180,5 @@ def _cell_index_pairs(self) -> List[pd.NonNegativeInt]:
         else:
             pairs = set(self.eme_grid_spec._cell_index_pairs)
         return list(pairs)
+
+    _boundaries_for_zero_dims = validate_boundaries_for_zero_dims()

tidy3d/components/mode/simulation.py

@@ -17,7 +17,7 @@
 from ..grid.grid_spec import GridSpec
 from ..mode_spec import ModeSpec
 from ..monitor import ModeMonitor, ModeSolverMonitor, PermittivityMonitor
-from ..simulation import AbstractYeeGridSimulation, Simulation
+from ..simulation import AbstractYeeGridSimulation, Simulation, validate_boundaries_for_zero_dims
 from ..source.field import ModeSource
 from ..types import (
     TYPE_TAG_STR,
@@ -513,3 +513,5 @@ def plot_pml_mode_plane(
 
     def validate_pre_upload(self, source_required: bool = False):
         self._mode_solver.validate_pre_upload(source_required=source_required)
+
+    _boundaries_for_zero_dims = validate_boundaries_for_zero_dims()

tidy3d/components/simulation.py

@@ -175,6 +175,59 @@
 FIXED_ANGLE_DT_SAFETY_FACTOR = 0.9
 
 
+def validate_boundaries_for_zero_dims():
+    """Error if absorbing boundaries, bloch boundaries, unmatching pec/pmc, or symmetry is used along a zero dimension."""
+
+    @pydantic.validator("boundary_spec", allow_reuse=True, always=True)
+    @skip_if_fields_missing(["size", "symmetry"])
+    def boundaries_for_zero_dims(cls, val, values):
+        """Error if absorbing boundaries, bloch boundaries, unmatching pec/pmc, or symmetry is used along a zero dimension."""
+        boundaries = val.to_list
+        size = values.get("size")
+        symmetry = values.get("symmetry")
+        axis_names = "xyz"
+
+        for dim, (boundary, symmetry_dim, size_dim) in enumerate(zip(boundaries, symmetry, size)):
+            if size_dim == 0:
+                axis = axis_names[dim]
+                num_absorbing_bdries = sum(isinstance(bnd, AbsorberSpec) for bnd in boundary)
+                num_bloch_bdries = sum(isinstance(bnd, BlochBoundary) for bnd in boundary)
+
+                if num_absorbing_bdries > 0:
+                    raise SetupError(
+                        f"The simulation has zero size along the {axis} axis, so "
+                        "using a PML or absorbing boundary along that axis is incorrect. "
+                        f"Use either 'Periodic' or 'BlochBoundary' along {axis}."
+                    )
+
+                if num_bloch_bdries > 0:
+                    raise SetupError(
+                        f"The simulation has zero size along the {axis} axis, "
+                        "using a Bloch boundary along such an axis is not supported because of "
+                        "the Bloch vector definition in units of '2 * pi / (size along dimension)'. Use a small "
+                        "but nonzero size along the dimension instead."
+                    )
+
+                if symmetry_dim != 0:
+                    raise SetupError(
+                        f"The simulation has zero size along the {axis} axis, so "
+                        "using symmetry along that axis is incorrect. Use 'PECBoundary' "
+                        "or 'PMCBoundary' to select source polarization if needed and set "
+                        f"Simulation.symmetry to 0 along {axis}."
+                    )
+
+                if boundary[0] != boundary[1]:
+                    raise SetupError(
+                        f"The simulation has zero size along the {axis} axis. "
+                        f"The boundary condition for {axis} plus and {axis} "
+                        "minus must be the same."
+                    )
+
+        return val
+
+    return boundaries_for_zero_dims
+
+
 class AbstractYeeGridSimulation(AbstractSimulation, ABC):
     """
     Abstract class for a simulation involving electromagnetic fields defined on a Yee grid.
@@ -2803,53 +2856,6 @@ def check_fixed_angle_components(cls, values):
 
         return values
 
-    @pydantic.validator("boundary_spec", always=True)
-    @skip_if_fields_missing(["size", "symmetry"])
-    def boundaries_for_zero_dims(cls, val, values):
-        """Error if absorbing boundaries, bloch boundaries, unmatching pec/pmc, or symmetry is used along a zero dimension."""
-        boundaries = val.to_list
-        size = values.get("size")
-        symmetry = values.get("symmetry")
-        axis_names = "xyz"
-
-        for dim, (boundary, symmetry_dim, size_dim) in enumerate(zip(boundaries, symmetry, size)):
-            if size_dim == 0:
-                axis = axis_names[dim]
-                num_absorbing_bdries = sum(isinstance(bnd, AbsorberSpec) for bnd in boundary)
-                num_bloch_bdries = sum(isinstance(bnd, BlochBoundary) for bnd in boundary)
-
-                if num_absorbing_bdries > 0:
-                    raise SetupError(
-                        f"The simulation has zero size along the {axis} axis, so "
-                        "using a PML or absorbing boundary along that axis is incorrect. "
-                        f"Use either 'Periodic' or 'BlochBoundary' along {axis}."
-                    )
-
-                if num_bloch_bdries > 0:
-                    raise SetupError(
-                        f"The simulation has zero size along the {axis} axis, "
-                        "using a Bloch boundary along such an axis is not supported because of "
-                        "the Bloch vector definition in units of '2 * pi / (size along dimension)'. Use a small "
-                        "but nonzero size along the dimension instead."
-                    )
-
-                if symmetry_dim != 0:
-                    raise SetupError(
-                        f"The simulation has zero size along the {axis} axis, so "
-                        "using symmetry along that axis is incorrect. Use 'PECBoundary' "
-                        "or 'PMCBoundary' to select source polarization if needed and set "
-                        f"Simulation.symmetry to 0 along {axis}."
-                    )
-
-                if boundary[0] != boundary[1]:
-                    raise SetupError(
-                        f"The simulation has zero size along the {axis} axis. "
-                        f"The boundary condition for {axis} plus and {axis} "
-                        "minus must be the same."
-                    )
-
-        return val
-
     @pydantic.validator("sources", always=True)
     def _validate_num_sources(cls, val):
         """Error if too many sources present."""
@@ -5201,3 +5207,5 @@ def from_scene(cls, scene: Scene, **kwargs) -> Simulation:
             medium=scene.medium,
             **kwargs,
         )
+
+    _boundaries_for_zero_dims = validate_boundaries_for_zero_dims()