feat: add interpolation to EME (FXC-4152)

caseyflex · caseyflex · commit 4bc3c7b9a6cc · 2025-11-18T18:11:49.000Z
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -38,6 +38,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `interp_spec` in `ModeSpec` to allow downsampling and interpolation of waveguide modes in frequency.
 - Added warning if port mesh refinement is incompatible with the `GridSpec` in the `TerminalComponentModeler`.
 - Various types, e.g. different `Simulation` or `SimulationData` sub-classes, can be loaded from file directly with `Tidy3dBaseModel.from_file()`.
+- Added `interp_spec` in `EMEModeSpec` to enable faster multi-frequency EME simulations. Note that the default is now `ModeInterpSpec.cheb(num_points=3, reduce_data=True)`; previously the computation was repeated at all frequencies.
 
 ### Breaking Changes
 - Edge singularity correction at PEC and lossy metal edges defaults to `True`.
@@ -64,6 +65,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Simulation data of batch jobs are now automatically downloaded upon their individual completion in `Batch.run()`, avoiding waiting for the entire batch to reach completion.
 - Port names in `ModalComponentModeler` and `TerminalComponentModeler` can no longer include the `@` symbol.
 - Improved speed of convolutions for large inputs.
+- Default value of `EMEModeSpec.interp_spec` is `ModeInterpSpec.cheb(num_points=3, reduce_data=True)` for faster multi-frequency EME simulations.
 
 ### Fixed
 - Ensured the legacy `Env` proxy mirrors `config.web` profile switches and preserves API URL.
diff --git a/schemas/EMESimulation.json b/schemas/EMESimulation.json
@@ -5294,7 +5294,18 @@
             {
               "$ref": "#/definitions/ModeInterpSpec"
             }
-          ]
+          ],
+          "default": {
+            "attrs": {},
+            "method": "poly",
+            "reduce_data": true,
+            "sampling_spec": {
+              "attrs": {},
+              "num_points": 3,
+              "type": "ChebSampling"
+            },
+            "type": "ModeInterpSpec"
+          }
         },
         "num_modes": {
           "default": 1,
diff --git a/tests/sims/full_fdtd.h5 b/tests/sims/full_fdtd.h5
diff --git a/tests/sims/full_fdtd.json b/tests/sims/full_fdtd.json
@@ -2075,6 +2075,7 @@
                     "track_freq": "central",
                     "type": "ModeSortSpec"
                 },
+                "interp_spec": null,
                 "type": "ModeSpec"
             },
             "mode_index": 0,
@@ -2666,6 +2667,7 @@
                     "track_freq": "central",
                     "type": "ModeSortSpec"
                 },
+                "interp_spec": null,
                 "type": "ModeSpec"
             },
             "store_fields_direction": null,
diff --git a/tests/test_components/test_eme.py b/tests/test_components/test_eme.py
@@ -568,7 +568,8 @@ def test_eme_simulation():
     sim = sim_no_field.updated_copy(sweep_spec=td.EMELengthSweep(scale_factors=[1, 2]))
     assert not sim._sweep_modes
     assert sim._num_sweep == 2
-    sim = sim.updated_copy(sweep_spec=td.EMEFreqSweep(freq_scale_factors=[1, 2]))
+    with AssertLogLevel("WARNING", contains_str="'EMEFreqSweep' is deprecated"):
+        sim = sim.updated_copy(sweep_spec=td.EMEFreqSweep(freq_scale_factors=[1, 2]))
     assert sim._sweep_modes
     assert sim._num_sweep == 2
     assert sim._monitor_num_sweep(sim.monitors[0]) == 1
@@ -911,7 +912,9 @@ def _get_mode_solver_data(modes_out=False, num_modes=3):
         size=(td.inf, td.inf, 0),
         center=(0, 0, offset),
         freqs=[td.C_0],
-        mode_spec=td.ModeSpec(num_modes=num_modes),
+        mode_spec=td.ModeSpec(
+            num_modes=num_modes, interp_spec=td.ModeInterpSpec.cheb(num_points=3, reduce_data=True)
+        ),
         name=name,
     )
     eme_mode_data = _get_eme_mode_solver_data()
diff --git a/tests/test_components/test_mode_interp.py b/tests/test_components/test_mode_interp.py
@@ -244,14 +244,14 @@ def test_mode_solver_monitor_valid_with_tracking():
 
 
 def test_interp_num_points_less_than_freqs():
-    """Test that num_points must be less than total freqs."""
+    """Test that num_points can be greater than total freqs."""
     mode_spec = td.ModeSpec(
         num_modes=2,
         sort_spec=td.ModeSortSpec(track_freq="central"),
         interp_spec=td.ModeInterpSpec.uniform(num_points=25, method="linear"),
     )
 
-    with AssertLogLevel("WARNING", contains_str="num_points"):
+    with AssertLogLevel(None):
         td.ModeSolverMonitor(
             center=(0, 0, 0),
             size=SIZE_2D,
@@ -262,14 +262,14 @@ def test_interp_num_points_less_than_freqs():
 
 
 def test_interp_num_points_equal_to_freqs():
-    """Test that num_points equal to freqs is rejected."""
+    """Test that num_points equal to freqs is not rejected."""
     mode_spec = td.ModeSpec(
         num_modes=2,
         sort_spec=td.ModeSortSpec(track_freq="central"),
         interp_spec=td.ModeInterpSpec.uniform(num_points=20, method="linear"),
     )
 
-    with AssertLogLevel("WARNING", contains_str="num_points"):
+    with AssertLogLevel(None):
         td.ModeSolverMonitor(
             center=(0, 0, 0),
             size=SIZE_2D,
@@ -354,7 +354,7 @@ def test_mode_solver_valid_with_tracking():
 
 @td.packaging.disable_local_subpixel
 def test_mode_solver_warns_num_points():
-    """Test that ModeSolver warns when num_points >= num_freqs."""
+    """Test that ModeSolver does not warn when num_points >= num_freqs."""
     sim = get_simple_sim()
     mode_spec = td.ModeSpec(
         num_modes=2,
@@ -363,14 +363,14 @@ def test_mode_solver_warns_num_points():
     )
     plane = td.Box(center=(0, 0, 0), size=SIZE_2D)
 
-    with AssertLogLevel("WARNING", contains_str="Interpolation will be skipped"):
+    with AssertLogLevel(None):
         ms = ModeSolver(
             simulation=sim,
             plane=plane,
             freqs=FREQS_DENSE,
             mode_spec=mode_spec,
         )
-        _ = ms.data_raw
+    _ = ms.data_raw
 
 
 def test_mode_solver_interp_spec_none():
@@ -1041,15 +1041,15 @@ def test_mode_solver_monitor_with_interp_spec():
 
 
 def test_mode_monitor_warns_redundant_num_points():
-    """Test warning when num_points >= number of frequencies in ModeMonitor."""
+    """Test no warning when num_points >= number of frequencies in ModeMonitor."""
     freqs = np.linspace(1e14, 2e14, 5)
     mode_spec = td.ModeSpec(
         num_modes=2,
         sort_spec=td.ModeSortSpec(track_freq="central"),
         interp_spec=td.ModeInterpSpec.uniform(num_points=5, method="linear"),
     )
 
-    with AssertLogLevel("WARNING", contains_str="Interpolation will be skipped"):
+    with AssertLogLevel(None):
         td.ModeMonitor(
             center=(0, 0, 0),
             size=SIZE_2D,
@@ -1060,15 +1060,15 @@ def test_mode_monitor_warns_redundant_num_points():
 
 
 def test_mode_solver_monitor_warns_redundant_num_points():
-    """Test warning when num_points >= number of frequencies in ModeSolverMonitor."""
+    """Test no warning when num_points >= number of frequencies in ModeSolverMonitor."""
     freqs = np.linspace(1e14, 2e14, 5)
     mode_spec = td.ModeSpec(
         num_modes=2,
         sort_spec=td.ModeSortSpec(track_freq="central"),
         interp_spec=td.ModeInterpSpec.uniform(num_points=6, method="linear"),
     )
 
-    with AssertLogLevel("WARNING", contains_str="Interpolation will be skipped"):
+    with AssertLogLevel(None):
         td.ModeSolverMonitor(
             center=(0, 0, 0),
             size=SIZE_2D,
diff --git a/tidy3d/components/data/dataset.py b/tidy3d/components/data/dataset.py
@@ -139,6 +139,10 @@ def _interp_dataarray_in_freq(
         DataArray
             Interpolated data array with the same structure but new frequency points.
         """
+        # if dataarray is already stored at the correct frequencies, do nothing
+        if np.array_equal(freqs, data.f):
+            return data
+
         # Map 'poly' to xarray's 'barycentric' method
         xr_method = "barycentric" if method == "poly" else method
 
diff --git a/tidy3d/components/data/monitor_data.py b/tidy3d/components/data/monitor_data.py
@@ -1286,6 +1286,22 @@ def to_zbf(
 
         return e_x, e_y
 
+    def _interpolated_copies_if_needed(
+        self, other: ElectromagneticFieldData
+    ) -> tuple[ElectromagneticFieldData, ElectromagneticFieldData]:
+        """Return interpolated copies of self, other if needed (different interp_spec)."""
+        mode_spec1 = self.monitor.mode_spec if isinstance(self, ModeSolverData) else None
+        mode_spec2 = other.monitor.mode_spec if isinstance(other, ModeSolverData) else None
+        if (
+            mode_spec1 is not None
+            and mode_spec2 is not None
+            and self.monitor.mode_spec._same_nontrivial_interp_spec(other=other.monitor.mode_spec)
+        ):
+            return self, other
+        self_copy = self.interpolated_copy if isinstance(self, ModeSolverData) else self
+        other_copy = other.interpolated_copy if isinstance(other, ModeSolverData) else other
+        return self_copy, other_copy
+
 
 class FieldData(FieldDataset, ElectromagneticFieldData):
     """
@@ -2685,6 +2701,8 @@ def _reduced_data(self) -> bool:
     @property
     def interpolated_copy(self) -> ModeSolverData:
         """Return a copy of the data with interpolated fields."""
+        if self.monitor.mode_spec.interp_spec is None:
+            return self
         if not self._reduced_data:
             return self
         interpolated_data = self.interp_in_freq(
diff --git a/tidy3d/components/eme/data/sim_data.py b/tidy3d/components/eme/data/sim_data.py
@@ -197,11 +197,19 @@ def smatrix_in_basis(
             modes1 = port_modes1
         if not modes2_provided:
             modes2 = port_modes2
-        f1 = list(modes1.field_components.values())[0].f.values
-        f2 = list(modes2.field_components.values())[0].f.values
+        f1 = list(modes1.monitor.freqs)
+        f2 = list(modes2.monitor.freqs)
 
         f = np.array(sorted(set(f1).intersection(f2).intersection(self.simulation.freqs)))
 
+        mode_spec1 = modes1.monitor.mode_spec if isinstance(modes1, ModeData) else None
+        mode_spec2 = modes2.monitor.mode_spec if isinstance(modes2, ModeData) else None
+
+        interp_spec1 = mode_spec1.interp_spec if mode_spec1 is not None else None
+        interp_spec2 = mode_spec2.interp_spec if mode_spec2 is not None else None
+
+        modes1, modes2 = modes1._interpolated_copies_if_needed(other=modes2)
+
         modes_in_1 = "mode_index" in list(modes1.field_components.values())[0].coords
         modes_in_2 = "mode_index" in list(modes2.field_components.values())[0].coords
 
@@ -259,6 +267,10 @@ def smatrix_in_basis(
                 overlaps1 = modes1.outer_dot(port_modes1, conjugate=False)
                 if not modes_in_1:
                     overlaps1 = overlaps1.expand_dims(dim={"mode_index_0": mode_index_1}, axis=1)
+                if interp_spec1 is not None:
+                    overlaps1 = modes1._interp_dataarray_in_freq(
+                        overlaps1, freqs=f, method=interp_spec1.method
+                    )
                 O1 = overlaps1.sel(f=f, mode_index_1=keep_mode_inds1)
 
                 O1out = O1.rename(mode_index_0="mode_index_out", mode_index_1="mode_index_out_old")
@@ -288,6 +300,10 @@ def smatrix_in_basis(
                 overlaps2 = modes2.outer_dot(port_modes2, conjugate=False)
                 if not modes_in_2:
                     overlaps2 = overlaps2.expand_dims(dim={"mode_index_0": mode_index_2}, axis=1)
+                if interp_spec2 is not None:
+                    overlaps2 = modes2._interp_dataarray_in_freq(
+                        overlaps2, freqs=f, method=interp_spec2.method
+                    )
                 O2 = overlaps2.sel(f=f, mode_index_1=keep_mode_inds2)
 
                 O2out = O2.rename(mode_index_0="mode_index_out", mode_index_1="mode_index_out_old")
diff --git a/tidy3d/components/eme/grid.py b/tidy3d/components/eme/grid.py
@@ -11,9 +11,9 @@
 from tidy3d.components.base import Tidy3dBaseModel, skip_if_fields_missing
 from tidy3d.components.geometry.base import Box
 from tidy3d.components.grid.grid import Coords1D
-from tidy3d.components.mode_spec import ModeSpec
+from tidy3d.components.mode_spec import ModeInterpSpec, ModeSpec
 from tidy3d.components.structure import Structure
-from tidy3d.components.types import ArrayFloat1D, Axis, Coordinate, Size, TrackFreq
+from tidy3d.components.types import ArrayFloat1D, Axis, Coordinate, Size
 from tidy3d.constants import RADIAN, fp_eps, inf
 from tidy3d.exceptions import SetupError, ValidationError
 
@@ -26,13 +26,14 @@
 class EMEModeSpec(ModeSpec):
     """Mode spec for EME cells. Overrides some of the defaults and allowed values."""
 
-    track_freq: Union[TrackFreq, None] = pd.Field(
-        None,
-        title="Mode Tracking Frequency",
-        description="Parameter that turns on/off mode tracking based on their similarity. "
-        "Can take values ``'lowest'``, ``'central'``, or ``'highest'``, which correspond to "
-        "mode tracking based on the lowest, central, or highest frequency. "
-        "If ``None`` no mode tracking is performed, which is the default for best performance.",
+    interp_spec: Optional[ModeInterpSpec] = pd.Field(
+        ModeInterpSpec.cheb(num_points=3, reduce_data=True),
+        title="Mode frequency interpolation specification",
+        description="Specification for computing modes at a reduced set of frequencies and "
+        "interpolating to obtain results at all requested frequencies. This can significantly "
+        "reduce computational cost for broadband simulations where modes vary smoothly with "
+        "frequency. Requires frequency tracking to be enabled (``sort_spec.track_freq`` must "
+        "not be ``None``) to ensure consistent mode ordering across frequencies.",
     )
 
     angle_theta: Literal[0.0] = pd.Field(
diff --git a/tidy3d/components/eme/simulation.py b/tidy3d/components/eme/simulation.py
@@ -722,6 +722,12 @@ def _validate_sweep_spec(self) -> None:
                         "which is not compatible with 'EMELengthSweep'."
                     )
         elif isinstance(self.sweep_spec, EMEFreqSweep):
+            log.warning(
+                "'EMEFreqSweep' is deprecated. Instead, it is recommended to use "
+                "'EMESimulation.freqs' directly, and set "
+                "'EMEModeSpec.interp_spec' as desired to balance "
+                "performance and accuracy."
+            )
             for i, scale_factor in enumerate(self.sweep_spec.freq_scale_factors):
                 scaled_freqs = np.array(self.freqs) * scale_factor
                 if np.min(scaled_freqs) < MIN_FREQUENCY:
@@ -1007,6 +1013,18 @@ def _monitor_freqs(self, monitor: Monitor) -> list[pd.NonNegativeFloat]:
             return list(self.freqs)
         return list(monitor.freqs)
 
+    def _monitor_mode_freqs(self, monitor: EMEModeSolverMonitor) -> list[pd.NonNegativeFloat]:
+        """Monitor frequencies."""
+        freqs = set()
+        cell_inds = self._monitor_eme_cell_indices(monitor=monitor)
+        for cell_ind in cell_inds:
+            interp_spec = self.eme_grid.mode_specs[cell_ind].interp_spec
+            if interp_spec is None:
+                freqs |= set(self.freqs)
+            else:
+                freqs |= set(interp_spec.sampling_points(self.freqs))
+        return list(freqs)
+
     def _monitor_num_freqs(self, monitor: Monitor) -> int:
         """Total number of freqs included in monitor."""
         return len(self._monitor_freqs(monitor=monitor))
diff --git a/tidy3d/components/mode/mode_solver.py b/tidy3d/components/mode/mode_solver.py
@@ -75,7 +75,6 @@
 from tidy3d.components.types.mode_spec import ModeSpecType
 from tidy3d.components.types.monitor_data import ModeSolverDataType
 from tidy3d.components.validators import (
-    _warn_interp_num_points,
     validate_freqs_min,
     validate_freqs_not_empty,
 )
@@ -515,9 +514,6 @@ def data_raw(self) -> ModeSolverDataType:
             A mode solver data type object containing the effective index and mode fields.
         """
 
-        if self.mode_spec.interp_spec is not None:
-            _warn_interp_num_points(self.mode_spec.interp_spec, self.freqs)
-
         if self.mode_spec.angle_rotation and np.abs(self.mode_spec.angle_theta) > 0:
             return self.rotated_mode_solver_data
 
diff --git a/tidy3d/components/mode/simulation.py b/tidy3d/components/mode/simulation.py
@@ -26,7 +26,6 @@
 from tidy3d.components.source.field import ModeSource
 from tidy3d.components.types import TYPE_TAG_STR, Ax, Direction, EMField, FreqArray
 from tidy3d.components.types.mode_spec import ModeSpecType
-from tidy3d.components.validators import validate_interp_num_points
 from tidy3d.constants import C_0
 from tidy3d.exceptions import SetupError, ValidationError
 from tidy3d.log import log
@@ -235,8 +234,6 @@ def plane_in_sim_bounds(cls, val, values):
             raise SetupError("'ModeSimulation.plane' must intersect 'ModeSimulation.geometry.")
         return val
 
-    _warn_interp_num_points = validate_interp_num_points()
-
     def _post_init_validators(self) -> None:
         """Call validators taking `self` that get run after init."""
         _ = self._mode_solver
diff --git a/tidy3d/components/mode_spec.py b/tidy3d/components/mode_spec.py
@@ -433,7 +433,7 @@ def sampling_points(self, freqs: FreqArray) -> FreqArray:
         >>> interp_spec = ModeInterpSpec.cheb(num_points=10)
         >>> sampling_freqs = interp_spec.sampling_points(freqs)
         """
-        if self.num_points > len(freqs):
+        if self.num_points >= len(freqs):
             return freqs
         return self.sampling_spec.sampling_points(freqs)
 
@@ -738,6 +738,14 @@ def _is_interp_spec_applied(self, freqs: FreqArray) -> bool:
         """Whether interp_spec is used to compute modes at the given frequencies."""
         return self.interp_spec is not None and self.interp_spec.num_points < len(freqs)
 
+    def _same_nontrivial_interp_spec(self, other: ModeSpec) -> bool:
+        """Whether two mode specs have identical nontrivial interp specs."""
+        return (
+            self.interp_spec is not None
+            and other.interp_spec is not None
+            and self.interp_spec == other.interp_spec
+        )
+
 
 class ModeSpec(AbstractModeSpec):
     """
diff --git a/tidy3d/components/monitor.py b/tidy3d/components/monitor.py
diff --git a/tidy3d/components/validators.py b/tidy3d/components/validators.py
