chore: Move nonlinear models to separate file

Author: caseyflex

tests/test_components/test_medium.py

@@ -720,30 +720,24 @@ def test_nonlinear_medium():
         monitors=[monitor],
         structures=[structure],
     )
-    assert n0 == nonlinear_spec.models[0]._get_n0(n0=None, medium=medium, freqs=[freq0])
-    assert freq0 == nonlinear_spec.models[0]._get_freq0(freq0=None, freqs=[freq0])
 
-    # subsection with nonlinear materials needs to hardcode source info
+    # subsection with nonlinear materials preserves sources
     sim2 = sim.updated_copy(center=(-4, -4, -4), path="sources/0")
     sim2 = sim2.updated_copy(
         models=[td.TwoPhotonAbsorption(beta=1)], path="structures/0/medium/nonlinear_spec"
     )
     sim2 = sim2.subsection(region=td.Box(center=(0, 0, 0), size=(1, 1, 0)))
-    assert sim2.structures[0].medium.nonlinear_spec.models[0].n0 == n0
-    assert sim2.structures[0].medium.nonlinear_spec.models[0].freq0 == freq0
 
     nonlinear_spec = td.NonlinearSpec(models=[td.KerrNonlinearity(n2=1, n0=1)])
     structure = structure.updated_copy(medium=medium.updated_copy(nonlinear_spec=nonlinear_spec))
     sim = sim.updated_copy(structures=[structure])
-    assert 1 == nonlinear_spec.models[0]._get_n0(n0=1, medium=medium, freqs=[1, 2])
 
     nonlinear_spec = td.NonlinearSpec(models=[td.TwoPhotonAbsorption(beta=1, n0=1)])
     structure = structure.updated_copy(medium=medium.updated_copy(nonlinear_spec=nonlinear_spec))
     sim = sim.updated_copy(structures=[structure])
     nonlinear_spec = td.NonlinearSpec(models=[td.TwoPhotonAbsorption(beta=1, n0=1, freq0=1)])
     structure = structure.updated_copy(medium=medium.updated_copy(nonlinear_spec=nonlinear_spec))
     sim = sim.updated_copy(structures=[structure])
-    assert 1 == nonlinear_spec.models[0]._get_freq0(freq0=1, freqs=[1, 2])
 
     # active materials with automatic detection of n0
     nonlinear_spec_active = td.NonlinearSpec(models=[td.TwoPhotonAbsorption(beta=-1)])

tidy3d/__init__.py

@@ -318,22 +318,17 @@
     FullyAnisotropicMedium,
     HammerstadSurfaceRoughness,
     HuraySurfaceRoughness,
-    KerrNonlinearity,
     Lorentz,
     LossyMetalMedium,
     Medium,
     Medium2D,
-    NonlinearModel,
-    NonlinearSpec,
-    NonlinearSusceptibility,
     PECMedium,
     PerturbationMedium,
     PerturbationPoleResidue,
     PMCMedium,
     PoleResidue,
     Sellmeier,
     SurfaceImpedanceFitterParam,
-    TwoPhotonAbsorption,
     medium_from_nk,
 )
 from .components.mode.data.sim_data import ModeSimulationData
@@ -363,6 +358,15 @@
     Monitor,
     PermittivityMonitor,
 )
+
+# nonlinear
+from .components.nonlinear import (
+    KerrNonlinearity,
+    NonlinearModel,
+    NonlinearSpec,
+    NonlinearSusceptibility,
+    TwoPhotonAbsorption,
+)
 from .components.parameter_perturbation import (
     CustomChargePerturbation,
     CustomHeatPerturbation,