Validate the use of dielectrics only in RectangularDielectric (#1859)

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

tests/test_plugins/test_waveguide.py

@@ -46,6 +46,40 @@ def test_array_validators():
         )
 
 
+def test_non_metallic_validator():
+    with pytest.raises(ValidationError, match="conductor"):
+        waveguide.RectangularDielectric(
+            wavelength=1.55,
+            core_width=0.3,
+            core_thickness=0.22,
+            clad_thickness=[1, 1],
+            core_medium=td.material_library["Ag"].medium,
+            clad_medium=[td.Medium(permittivity=1.45**2)] * 2,
+        )
+
+    with pytest.raises(ValidationError, match="conductor"):
+        waveguide.RectangularDielectric(
+            wavelength=1.55,
+            core_width=0.3,
+            core_thickness=0.22,
+            clad_thickness=1,
+            core_medium=td.Medium(permittivity=3.48**2),
+            clad_medium=td.material_library["Ag"].medium,
+        )
+
+    with pytest.raises(ValidationError, match="conductor"):
+        waveguide.RectangularDielectric(
+            wavelength=1.55,
+            core_width=0.3,
+            core_thickness=0.22,
+            clad_thickness=[1, 1],
+            box_thickness=[1, 1],
+            core_medium=td.Medium(permittivity=3.48**2),
+            clad_medium=[td.Medium(permittivity=1.45**2)] * 2,
+            box_medium=[td.Medium(permittivity=1.45**2), td.material_library["Ag"].medium],
+        )
+
+
 def test_layer_validators():
     with pytest.raises(ValidationError, match="Number"):
         waveguide.RectangularDielectric(

tidy3d/plugins/waveguide/rectangular_dielectric.py

@@ -215,6 +215,19 @@ def _set_non_negative_array(cls, val):
             raise ValidationError("Values may not be negative.")
         return val
 
+    @pydantic.validator("core_medium", "clad_medium", "box_medium")
+    def _check_non_metallic(cls, val, values):
+        if val is None:
+            return val
+        media = val if isinstance(val, tuple) else (val,)
+        freqs = C_0 / values["wavelength"]
+        if any(medium.eps_model(f).real < 1 for medium in media for f in freqs):
+            raise ValidationError(
+                "'RectangularDielectric' can only be used with dielectric media. "
+                "Found a conductor with real permittivity < 1."
+            )
+        return val
+
     @pydantic.validator("gap", always=True)
     @skip_if_fields_missing(["core_width"])
     def _validate_gaps(cls, val, values):