Added bend_angle_rotation in mode_spec

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Users can manually specify the background medium for a structure to be used for geometry gradient calculations by supplying `Structure.background_permittivity`. This is useful when there are overlapping structures or structures embedded in other mediums.
 - Autograd functions can now be called directly on `DataArray` (e.g., `np.sum(data_array)`) in objective functions.
 - Automatic differentiation support for local field projections with `FieldProjectionAngleMonitor` and `FieldProjectionCartesianMonitor` using `FieldProjector.project_fields(far_field_monitor)`.
+- `bend_angle_rotation` in `mode_spec` to improve accuracy when both bend and angle are defined."
 
 ### Changed
 - Improved autograd tracer handling in `DataArray`, resulting in significant speedups for differentiation involving large monitors.

tidy3d/__init__.py

@@ -57,6 +57,7 @@
     PointDataArray,
     ScalarFieldDataArray,
     ScalarFieldTimeDataArray,
+    ScalarModeFieldCylindricalDataArray,
     ScalarModeFieldDataArray,
     SpatialDataArray,
 )
@@ -371,6 +372,7 @@ def set_logging_level(level: str) -> None:
     "FieldProjector",
     "ScalarFieldDataArray",
     "ScalarModeFieldDataArray",
+    "ScalarModeFieldCylindricalDataArray",
     "ScalarFieldTimeDataArray",
     "SpatialDataArray",
     "ModeAmpsDataArray",

tidy3d/components/data/data_array.py

@@ -822,6 +822,24 @@ class ScalarModeFieldDataArray(AbstractSpatialDataArray):
     _dims = ("x", "y", "z", "f", "mode_index")
 
 
+class ScalarModeFieldCylindricalDataArray(AbstractSpatialDataArray):
+    """Spatial distribution of a mode in frequency-domain as a function of mode index.
+
+    Example
+    -------
+    >>> rho = [1,2]
+    >>> theta = [2,3,4]
+    >>> axial = [3,4,5,6]
+    >>> f = [2e14, 3e14]
+    >>> mode_index = np.arange(5)
+    >>> coords = dict(rho=rho, theta=theta, axial=axial, f=f, mode_index=mode_index)
+    >>> fd = ScalarModeFieldCylindricalDataArray((1+1j) * np.random.random((2,3,4,2,5)), coords=coords)
+    """
+
+    __slots__ = ()
+    _dims = ("rho", "theta", "axial", "f", "mode_index")
+
+
 class FluxDataArray(DataArray):
     """Flux through a surface in the frequency-domain.
 

tidy3d/components/data/dataset.py

@@ -32,6 +32,7 @@
     PointDataArray,
     ScalarFieldDataArray,
     ScalarFieldTimeDataArray,
+    ScalarModeFieldCylindricalDataArray,
     ScalarModeFieldDataArray,
     SpatialDataArray,
     TimeDataArray,
@@ -149,6 +150,7 @@ def colocate(self, x=None, y=None, z=None) -> xr.Dataset:
     ScalarFieldDataArray,
     ScalarFieldTimeDataArray,
     ScalarModeFieldDataArray,
+    ScalarModeFieldCylindricalDataArray,
     EMEScalarModeFieldDataArray,
     EMEScalarFieldDataArray,
 ]

tidy3d/components/mode.py

@@ -127,6 +127,18 @@ class ModeSpec(Tidy3dBaseModel):
         "yz plane, the ``bend_axis`` is always 1 (the global z axis).",
     )
 
+    bend_angle_rotation: bool = pd.Field(
+        False,
+        title="Use fields rotation when both bend and angle are defined",
+        description="Defines how modes are computed when both a bend and an angle are defined. "
+        " If `False`, the two coordinate transformations are directly composed. If `True`, the "
+        "structures in the simulation are first rotated, to compute a mode solution at a reference"
+        "plane normal to the bend's azimuthal direction. Then, the fields are rotated to align with"
+        "the mode plane, using the `n_eff` calculated at the reference plane. The second option can"
+        "produce more accurate results, but more care must be taken for example in ensuring that the"
+        "original mode plane intersects the right geometries in the simulation with rotated structures.",
+    )
+
     track_freq: Union[TrackFreq, None] = pd.Field(
         "central",
         title="Mode Tracking Frequency",
@@ -160,6 +172,17 @@ def bend_radius_not_zero(cls, val, values):
             raise SetupError("The magnitude of 'bend_radius' must be larger than 0.")
         return val
 
+    @pd.validator("bend_angle_rotation", always=True)
+    @skip_if_fields_missing(["bend_radius", "bend_axis"])
+    def validate_bend_correction_requirements(cls, val, values):
+        """Ensure that both ``bend_axis`` and ``bend_radius`` are provided if ``bend_correction`` is enabled."""
+        if val is True:
+            if values.get("bend_axis") is None or values.get("bend_radius") is None:
+                raise SetupError(
+                    "'bend_correction' can only be enabled when both 'bend_axis' and 'bend_radius' are provided."
+                )
+        return val
+
     @pd.validator("angle_theta", allow_reuse=True, always=True)
     def glancing_incidence(cls, val):
         """Warn if close to glancing incidence."""