Add interpolation to EME

Author: caseyflex

CHANGELOG.md

@@ -36,6 +36,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `tidy3d.plugins.design.DesignSpace.run(..., fn_post=...)` now accepts a `priority` keyword to propagate vGPU queue priority to all automatically batched simulations.
 - Introduced `BroadbandPulse` for exciting simulations across a wide frequency spectrum.
 - Added `interp_spec` in `ModeSpec` to allow downsampling and interpolation of waveguide modes in frequency.
+- Added `interp_spec` in `EMEModeSpec` to enable faster multi-frequency EME simulations.
 
 ### Breaking Changes
 - Edge singularity correction at PEC and lossy metal edges defaults to `True`.

tests/test_components/test_eme.py

@@ -911,7 +911,9 @@ 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()

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
 

tidy3d/components/eme/data/sim_data.py

@@ -197,11 +197,27 @@ 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)))
 
+        interp_spec1 = (
+            modes1.monitor.mode_spec.interp_spec if isinstance(modes1, ModeData) else None
+        )
+        interp_spec2 = (
+            modes2.monitor.mode_spec.interp_spec if isinstance(modes2, ModeData) else None
+        )
+
+        interp_overlaps = False
+        if interp_spec1 is not None and interp_spec2 is not None and interp_spec1 == interp_spec2:
+            interp_overlaps = True
+        else:
+            if interp_spec1 is not None:
+                modes1 = modes1.interpolated_copy
+            if interp_spec2 is not None:
+                modes2 = modes2.interpolated_copy
+
         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 +275,10 @@ 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_overlaps:
+                    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 +308,10 @@ 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_overlaps:
+                    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")

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(

tidy3d/components/eme/simulation.py

@@ -1007,6 +1007,18 @@ 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))

tidy3d/components/mode/mode_solver.py

@@ -515,8 +515,8 @@ 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.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

tidy3d/components/monitor.py

@@ -437,7 +437,7 @@ def _storage_size_solver(self, num_cells: int, tmesh: ArrayFloat1D) -> int:
             return 2 * bytes_single
         return bytes_single
 
-    _warn_interp_num_points = validate_interp_num_points()
+    # _warn_interp_num_points = validate_interp_num_points()
 
 
 class FieldMonitor(AbstractFieldMonitor, FreqMonitor):