Geometry edges over field plots and fix mode solver plot return (#1628)

Signed-off-by: Lucas Heitzmann Gabrielli <lucas@flexcompute.com>

CHANGELOG.md

@@ -5,6 +5,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- `RectangularWaveguide.plot_field` optionally draws geometry edges over fields. 
+
+### Fixed
+- `ModeSolver.plot_field` correctly returning the plot axes.
+
 ## [2.7.0rc2] - 2024-05-14
 
 ### Added

tidy3d/plugins/mode/mode_solver.py

@@ -970,7 +970,7 @@ def plot_field(
         """
 
         sim_data = self.sim_data
-        sim_data.plot_field(
+        return sim_data.plot_field(
             field_monitor_name=MODE_MONITOR_NAME,
             field_name=field_name,
             val=val,

tidy3d/plugins/waveguide/rectangular_dielectric.py

@@ -3,6 +3,7 @@
 from typing import List, Any
 
 import numpy
+from matplotlib import pyplot
 import pydantic.v1 as pydantic
 
 from ...components.base import Tidy3dBaseModel, cached_property, skip_if_fields_missing
@@ -14,6 +15,7 @@
 from ...components.medium import Medium, MediumType
 from ...components.mode import ModeSpec
 from ...components.simulation import Simulation
+from ...components.viz import add_ax_if_none
 
 from ...components.source import ModeSource, GaussianPulse
 from ...components.structure import Structure
@@ -915,6 +917,54 @@ def plot_grid(
             **kwargs,
         )
 
+    @add_ax_if_none
+    def plot_geometry_edges(
+        self,
+        color: str = "k",
+        ax: Ax = None,
+    ) -> Ax:
+        """Plot the waveguide cross-section geometry edges.
+
+        Parameters
+        ----------
+        color : Color to use for the geometry edges.
+        ax : matplotlib.axes._subplots.Axes = None
+            matplotlib axes to plot on, if not specified, one is created.
+
+        Returns
+        -------
+        matplotlib.axes._subplots.Axes
+            The supplied or created matplotlib axes.
+        """
+        kwargs = {"color": color, "linewidth": pyplot.rcParams["grid.linewidth"]}
+        if self.normal_axis < self.lateral_axis:
+            x0 = self.origin[self.lateral_axis]
+            ax.axvline(x0 + self.core_thickness + self.clad_thickness, **kwargs)
+            ax.axvline(x0, **kwargs)
+            ax.axvline(x0 - self.box_thickness, **kwargs)
+        else:
+            y0 = self.origin[self.normal_axis]
+            ax.axhline(y0 + self.core_thickness + self.clad_thickness, **kwargs)
+            ax.axhline(y0, **kwargs)
+            ax.axhline(y0 - self.box_thickness, **kwargs)
+
+        dx = self.core_thickness * numpy.tan(self.sidewall_angle)
+        u = min(self.lateral_axis, self.normal_axis)
+        v = max(self.lateral_axis, self.normal_axis)
+        for x0, w in zip(self._core_starts, self.core_width):
+            plot_x = []
+            plot_y = []
+            for x, y in zip(
+                [x0 - dx, x0, x0 + w, x0 + w + dx],
+                [0, self.core_thickness, self.core_thickness, 0],
+            ):
+                p = self._translate(x, y, 0)
+                plot_x.append(p[u])
+                plot_y.append(p[v])
+            ax.plot(plot_x, plot_y, linestyle="-", **kwargs)
+        ax.set_aspect("equal")
+        return ax
+
     def plot_field(
         self,
         field_name: str,
@@ -924,6 +974,7 @@ def plot_field(
         vmin: float = None,
         vmax: float = None,
         ax: Ax = None,
+        geometry_edges: str = None,
         **sel_kwargs,
     ) -> Ax:
         """Plot the field for a :class:`.ModeSolverData` with :class:`.Simulation` plot overlaid.
@@ -951,6 +1002,7 @@ def plot_field(
             inferred from the data and other keyword arguments.
         ax : matplotlib.axes._subplots.Axes = None
             matplotlib axes to plot on, if not specified, one is created.
+        geometry_edges : Optional color to use for the geometry edges overlaid on the fields.
         sel_kwargs : keyword arguments used to perform ``.sel()`` selection in the monitor data.
             These kwargs can select over the spatial dimensions (``x``, ``y``, ``z``),
             frequency or time dimensions (``f``, ``t``) or `mode_index`, if applicable.
@@ -963,7 +1015,7 @@ def plot_field(
         matplotlib.axes._subplots.Axes
             The supplied or created matplotlib axes.
         """
-        return self.mode_solver.plot_field(
+        ax = self.mode_solver.plot_field(
             field_name=field_name,
             val=val,
             eps_alpha=eps_alpha,
@@ -973,3 +1025,6 @@ def plot_field(
             ax=ax,
             **sel_kwargs,
         )
+        if geometry_edges is not None:
+            self.plot_geometry_edges(geometry_edges, ax=ax)
+        return ax