Grid correction to Poynting in 2D monitor (#839) (#1003)

Signed-off-by: Lucas Heitzmann Gabrielli <[email protected]>

Author: lucas-flexcompute

CHANGELOG.md

@@ -24,6 +24,7 @@ that the fields match exactly except for a ``pi`` phase shift. This interpretati
 - Point-like objects correctly appear as single points using `plt.scatter`.
 - Cleaner display of `ArrayLike` in docs.
 - `ArrayLike` validation properly fails with `None` or `nan` contents.
+- Apply finite grid correction to the fields when calculating the Poynting vector from 2D monitors.
 
 ## [2.3.0] - 2023-6-30
 

tidy3d/components/data/monitor_data.py

@@ -197,20 +197,16 @@ def _tangential_dims(self) -> List[str]:
         return tangential_dims
 
     @property
-    def _grid_corrected_fields(self) -> Dict[str, DataArray]:
+    def _in_plane(self) -> Dict[str, DataArray]:
         """Dictionary of field components with finite grid correction factors applied and symmetry
         expanded."""
         if len(self.monitor.zero_dims) != 1:
             raise DataError("Data must be 2D to apply grid corrections.")
+
         normal_dim = "xyz"[self.monitor.zero_dims[0]]
         fields = {}
-        for field_name, field in self.symmetry_expanded_copy.field_components.items():
-            eig_val = self.symmetry_eigenvalues[field_name](normal_dim)
-            if eig_val < 0:
-                fields[field_name] = field * self.grid_dual_correction
-            else:
-                fields[field_name] = field * self.grid_primal_correction
-            fields[field_name] = fields[field_name].squeeze(dim=normal_dim, drop=True)
+        for field_name, field in self.grid_corrected_copy.field_components.items():
+            fields[field_name] = field.squeeze(dim=normal_dim, drop=True)
         return fields
 
     @property
@@ -307,7 +303,7 @@ def _tangential_fields(self) -> Dict[str, DataArray]:
         ----
             The finite grid correction factors are applied and symmetry is expanded.
         """
-        return self._tangential_corrected(self._grid_corrected_fields)
+        return self._tangential_corrected(self._in_plane)
 
     @property
     def _centered_fields(self) -> Dict[str, DataArray]:
@@ -319,7 +315,8 @@ def _centered_fields(self) -> Dict[str, DataArray]:
             The finite grid correction factors are applied and symmetry is expanded.
         """
 
-        field_components = self._grid_corrected_fields
+        field_components = self._in_plane
+
         if self.monitor.colocate:
             return field_components
 
@@ -346,6 +343,24 @@ def _centered_tangential_fields(self) -> Dict[str, DataArray]:
         """
         return self._tangential_corrected(self._centered_fields)
 
+    @property
+    def grid_corrected_copy(self) -> ElectromagneticFieldData:
+        """Return a copy of self with grid correction factors applied (if necessary) and symmetry
+        expanded."""
+        field_data = self.symmetry_expanded_copy
+        if len(self.monitor.zero_dims) != 1:
+            return field_data
+
+        normal_dim = "xyz"[self.monitor.zero_dims[0]]
+        update = {"grid_primal_correction": 1.0, "grid_dual_correction": 1.0}
+        for field_name, field in field_data.field_components.items():
+            eig_val = self.symmetry_eigenvalues[field_name](normal_dim)
+            if eig_val < 0:
+                update[field_name] = field * self.grid_dual_correction
+            else:
+                update[field_name] = field * self.grid_primal_correction
+        return field_data.copy(update=update)
+
     @property
     def intensity(self) -> ScalarFieldDataArray:
         """Return the sum of the squared absolute electric field components."""

tidy3d/components/data/sim_data.py

@@ -216,8 +216,23 @@ def at_centers(self, field_monitor_name: str) -> xr.Dataset:
             interpolated to center locations on Yee grid.
         """
 
-        # get the data
-        monitor_data = self.load_field_monitor(field_monitor_name)
+        return self._at_centers(self.load_field_monitor(field_monitor_name))
+
+    def _at_centers(self, monitor_data: xr.Dataset) -> xr.Dataset:
+        """return xarray.Dataset representation of field monitor data
+        co-located at Yee cell centers.
+
+        Parameters
+        ----------
+        monitor_data : xr.Dataset
+            Monitor data to be co-located.
+
+        Returns
+        -------
+        xarray.Dataset
+            Dataset containing all of the fields in the data
+            interpolated to center locations on Yee grid.
+        """
 
         # discretize the monitor and get center locations
         sub_grid = self.simulation.discretize(monitor_data.monitor, extend=False)
@@ -233,6 +248,7 @@ def at_centers(self, field_monitor_name: str) -> xr.Dataset:
 
         return monitor_data.colocate(**xyz_kwargs)
 
+    # pylint: disable=too-many-locals
     def get_poynting_vector(self, field_monitor_name: str) -> xr.Dataset:
         """return ``xarray.Dataset`` of the Poynting vector at Yee cell centers.
 
@@ -253,8 +269,9 @@ def get_poynting_vector(self, field_monitor_name: str) -> xr.Dataset:
             DataArray containing the Poynting vector calculated based on the field components
             colocated at the center locations of the Yee grid.
         """
-
-        field_dataset = self.at_centers(field_monitor_name)
+        # Fields from 2D monitors need a correction factor
+        mon_data = self.load_field_monitor(field_monitor_name).grid_corrected_copy
+        field_dataset = self._at_centers(mon_data)
 
         time_domain = isinstance(self.monitor_data[field_monitor_name], FieldTimeData)