Set minimum PML layers to 6

CHANGELOG.md

@@ -15,10 +15,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `@scalar_objective` decorator in `tidy3d.plugins.autograd` that wraps objective functions to ensure they return a scalar value and performs additional checks to ensure compatibility of objective functions with autograd. Used by default in `tidy3d.plugins.autograd.value_and_grad` as well as `tidy3d.plugins.autograd.grad`.
 - Autograd support for simulations without adjoint sources in `run` as well as `run_async`, which will not attempt to run the simulation but instead return zero gradients. This can sometimes occur if the objective function gradient does not depend on some simulations, for example when using `min` or `max` in the objective.
 
-
 ### Changed
 - `CustomMedium` design regions require far less data when performing inverse design by reducing adjoint field monitor size for dims with one pixel.
-- Calling `.values` on `DataArray` no longer raises a `DeprecationWarning` during automatic differentiation
+- Calling `.values` on `DataArray` no longer raises a `DeprecationWarning` during automatic differentiation.
+- Minimum number of PML layers set to 6.
 
 ### Fixed
 - Regression in local field projection leading to incorrect results for `far_field_approx=True`.

tests/test_components/test_grid.py

@@ -108,7 +108,7 @@ def test_sim_nonuniform_small():
     # tests when the nonuniform grid does not cover the simulation size
 
     size_x = 18
-    num_layers_pml_x = 2
+    num_layers_pml_x = 6
     grid_size_x = [2, 1, 3]
     sim = td.Simulation(
         center=(1, 0, 0),
@@ -153,15 +153,12 @@ def test_sim_nonuniform_small():
     for dl in dls:
         assert dl in grid_size_x
 
-    # tests that it gives exactly what we expect
-    assert np.all(bound_coords == np.array([-12, -10, -8, -6, -4, -2, 0, 1, 4, 7, 10, 13, 16]))
-
 
 def test_sim_nonuniform_large():
     # tests when the nonuniform grid extends beyond the simulation size
 
     size_x = 18
-    num_layers_pml_x = 2
+    num_layers_pml_x = 6
     grid_size_x = [2, 3, 4, 1, 2, 1, 3, 1, 2, 3, 4]
     sim = td.Simulation(
         center=(1, 0, 0),
@@ -230,9 +227,9 @@ def test_sim_symmetry_grid():
         size=(11, 11, 11),
         grid_spec=td.GridSpec(grid_x=grid_1d, grid_y=grid_1d, grid_z=grid_1d),
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=2),
-            y=td.Boundary.pml(num_layers=2),
-            z=td.Boundary.pml(num_layers=2),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         symmetry=(0, 1, -1),
         run_time=1e-12,
@@ -257,20 +254,20 @@ def test_sim_pml_grid():
         size=(4, 4, 4),
         grid_spec=td.GridSpec.uniform(1.0),
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=2),
-            y=td.Boundary.absorber(num_layers=2),
-            z=td.Boundary.stable_pml(num_layers=2),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.absorber(num_layers=6),
+            z=td.Boundary.stable_pml(num_layers=6),
         ),
         run_time=1e-12,
     )
 
     for dim in "xyz":
         c = sim.grid.centers.dict()[dim]
-        assert np.all(c == np.array([-3.5, -2.5, -1.5, -0.5, 0.5, 1.5, 2.5, 3.5]))
+        assert np.all(c == np.arange(-7.5, 8, 1))
 
     for dim in "xyz":
         b = sim.grid.boundaries.dict()[dim]
-        assert np.all(b == np.array([-4, -3, -2, -1, 0, 1, 2, 3, 4]))
+        assert np.all(b == np.arange(-8, 8.5, 1))
 
 
 def test_sim_discretize_vol():

tests/test_components/test_grid_spec.py

@@ -171,9 +171,9 @@ def test_autogrid_2dmaterials():
         structures=[box],
         sources=[src],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         grid_spec=td.GridSpec.auto(),
         run_time=1e-12,
@@ -192,9 +192,9 @@ def test_autogrid_2dmaterials():
         structures=[box2],
         sources=[src],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         grid_spec=td.GridSpec.auto(),
         run_time=1e-12,
@@ -211,9 +211,9 @@ def test_autogrid_2dmaterials():
         structures=[box, box2],
         sources=[src],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         grid_spec=td.GridSpec.auto(),
         run_time=1e-12,

tests/test_components/test_simulation.py

@@ -832,9 +832,9 @@ def test_sim_structure_gap(log_capture, box_size, log_level):
         structures=[box],
         sources=[src],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         run_time=1e-12,
     )
@@ -2047,9 +2047,9 @@ def test_sim_volumetric_structures(log_capture, tmp_path):
             structures=[struct],
             sources=[src],
             boundary_spec=td.BoundarySpec(
-                x=td.Boundary.pml(num_layers=5),
-                y=td.Boundary.pml(num_layers=5),
-                z=td.Boundary.pml(num_layers=5),
+                x=td.Boundary.pml(num_layers=6),
+                y=td.Boundary.pml(num_layers=6),
+                z=td.Boundary.pml(num_layers=6),
             ),
             grid_spec=td.GridSpec.uniform(dl=grid_dl),
             run_time=1e-12,
@@ -2089,9 +2089,9 @@ def test_sim_volumetric_structures(log_capture, tmp_path):
         sources=[src],
         monitors=[monitor],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         grid_spec=td.GridSpec.uniform(dl=grid_dl),
         run_time=1e-12,
@@ -2114,9 +2114,9 @@ def test_sim_volumetric_structures(log_capture, tmp_path):
         sources=[src],
         monitors=[monitor],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         grid_spec=td.GridSpec.uniform(dl=grid_dl),
         run_time=1e-12,
@@ -2145,9 +2145,9 @@ def test_sim_volumetric_structures(log_capture, tmp_path):
         structures=[below_half, box],
         sources=[src],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         grid_spec=td.GridSpec.uniform(dl=grid_dl),
         run_time=1e-12,
@@ -2161,9 +2161,9 @@ def test_sim_volumetric_structures(log_capture, tmp_path):
         structures=[box, below],
         sources=[src],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
-            y=td.Boundary.pml(num_layers=5),
-            z=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
+            y=td.Boundary.pml(num_layers=6),
+            z=td.Boundary.pml(num_layers=6),
         ),
         grid_spec=td.GridSpec.uniform(dl=grid_dl),
         run_time=1e-12,
@@ -2179,9 +2179,9 @@ def test_sim_volumetric_structures(log_capture, tmp_path):
             sources=[src],
             medium=box.medium,
             boundary_spec=td.BoundarySpec(
-                x=td.Boundary.pml(num_layers=5),
-                y=td.Boundary.pml(num_layers=5),
-                z=td.Boundary.pml(num_layers=5),
+                x=td.Boundary.pml(num_layers=6),
+                y=td.Boundary.pml(num_layers=6),
+                z=td.Boundary.pml(num_layers=6),
             ),
             grid_spec=td.GridSpec.uniform(dl=grid_dl),
             run_time=1e-12,
@@ -2208,9 +2208,9 @@ def test_sim_volumetric_structures(log_capture, tmp_path):
             structures=[struct],
             sources=[src],
             boundary_spec=td.BoundarySpec(
-                x=td.Boundary.pml(num_layers=5),
-                y=td.Boundary.pml(num_layers=5),
-                z=td.Boundary.pml(num_layers=5),
+                x=td.Boundary.pml(num_layers=6),
+                y=td.Boundary.pml(num_layers=6),
+                z=td.Boundary.pml(num_layers=6),
             ),
             grid_spec=td.GridSpec.uniform(dl=grid_dl),
             run_time=1e-12,
@@ -2928,9 +2928,9 @@ def test_validate_low_num_cells_in_mode_objects():
         grid_spec=td.GridSpec(wavelength=1.0),
         sources=[mode_source],
         boundary_spec=td.BoundarySpec(
-            x=td.Boundary.pml(num_layers=5),
+            x=td.Boundary.pml(num_layers=6),
             y=td.Boundary.pec(),
-            z=td.Boundary.pml(num_layers=5),
+            z=td.Boundary.pml(num_layers=6),
         ),
     )
     sim2d._validate_num_cells_in_mode_objects()

tests/test_components/test_viz.py

@@ -56,7 +56,7 @@ def test_2d_boundary_plot():
 
     # Simulation details
     per_boundary = td.Boundary.periodic()
-    pml_boundary = td.Boundary.pml(num_layers=2)
+    pml_boundary = td.Boundary.pml(num_layers=6)
 
     sim = td.Simulation(
         size=(0, 1, 1),

tidy3d/components/boundary.py

@@ -16,6 +16,8 @@
 from .source import TFSF, GaussianBeam, ModeSource, PlaneWave
 from .types import TYPE_TAG_STR, Axis, Complex
 
+MIN_NUM_PML_LAYERS = 6
+
 
 class BoundaryEdge(ABC, Tidy3dBaseModel):
     """Electromagnetic boundary condition at a domain edge."""
@@ -260,10 +262,11 @@ class PMLParams(AbsorberParams):
 class AbsorberSpec(BoundaryEdge):
     """Specifies the generic absorber properties along a single dimension."""
 
-    num_layers: pd.NonNegativeInt = pd.Field(
+    num_layers: int = pd.Field(
         ...,
         title="Number of Layers",
         description="Number of layers of standard PML.",
+        ge=MIN_NUM_PML_LAYERS,
     )
     parameters: AbsorberParams = pd.Field(
         ...,
@@ -376,10 +379,11 @@ class PML(AbsorberSpec):
 
     """
 
-    num_layers: pd.NonNegativeInt = pd.Field(
+    num_layers: int = pd.Field(
         12,
         title="Number of Layers",
         description="Number of layers of standard PML.",
+        ge=MIN_NUM_PML_LAYERS,
     )
 
     parameters: PMLParams = pd.Field(
@@ -413,8 +417,11 @@ class StablePML(AbsorberSpec):
         * `Introduction to perfectly matched layer (PML) tutorial <https://www.flexcompute.com/fdtd101/Lecture-6-Introduction-to-perfectly-matched-layer/>`__
     """
 
-    num_layers: pd.NonNegativeInt = pd.Field(
-        40, title="Number of Layers", description="Number of layers of 'stable' PML."
+    num_layers: int = pd.Field(
+        40,
+        title="Number of Layers",
+        description="Number of layers of 'stable' PML.",
+        ge=MIN_NUM_PML_LAYERS,
     )
 
     parameters: PMLParams = pd.Field(
@@ -463,10 +470,11 @@ class Absorber(AbsorberSpec):
         * `How to troubleshoot a diverged FDTD simulation <../../notebooks/DivergedFDTDSimulation.html>`_
     """
 
-    num_layers: pd.NonNegativeInt = pd.Field(
+    num_layers: int = pd.Field(
         40,
         title="Number of Layers",
         description="Number of layers of absorber to add to + and - boundaries.",
+        ge=MIN_NUM_PML_LAYERS,
     )
 
     parameters: AbsorberParams = pd.Field(