Low freq extrapolation (FXC-2558)

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added support for `tidy3d-extras`, an optional plugin that enables more accurate local mode solving via subpixel averaging.
 - Added support for `symlog` and `log` scale plotting in `Scene.plot_eps()` and `Scene.plot_structures_property()` methods. The `symlog` scale provides linear behavior near zero and logarithmic behavior elsewhere, while 'log' is a base 10 logarithmic scale.
+- Added `LowFrequencySmoothingSpec` and `ModelerLowFrequencySmoothingSpec` for automatic smoothing of mode monitor data at low frequencies where DFT sampling is insufficient.
 
 ### Changed
 - Improved performance of antenna metrics calculation by utilizing cached wave amplitude calculations instead of recomputing wave amplitudes for each port excitation in the `TerminalComponentModelerData`.

schemas/Simulation.json

@@ -9350,6 +9350,53 @@
       ],
       "type": "object"
     },
+    "LowFrequencySmoothingSpec": {
+      "additionalProperties": false,
+      "properties": {
+        "attrs": {
+          "default": {},
+          "type": "object"
+        },
+        "max_deviation": {
+          "default": 0.5,
+          "minimum": 0,
+          "type": "number"
+        },
+        "max_sampling_time": {
+          "default": 5.0,
+          "minimum": 0,
+          "type": "number"
+        },
+        "min_sampling_time": {
+          "default": 1.0,
+          "minimum": 0,
+          "type": "number"
+        },
+        "monitors": {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        },
+        "order": {
+          "default": 1,
+          "maximum": 3,
+          "minimum": 0,
+          "type": "integer"
+        },
+        "type": {
+          "default": "LowFrequencySmoothingSpec",
+          "enum": [
+            "LowFrequencySmoothingSpec"
+          ],
+          "type": "string"
+        }
+      },
+      "required": [
+        "monitors"
+      ],
+      "type": "object"
+    },
     "LumpedResistor": {
       "additionalProperties": false,
       "properties": {
@@ -15539,6 +15586,13 @@
       },
       "type": "array"
     },
+    "low_freq_smoothing": {
+      "allOf": [
+        {
+          "$ref": "#/definitions/LowFrequencySmoothingSpec"
+        }
+      ]
+    },
     "lumped_elements": {
       "default": [],
       "items": {

schemas/TerminalComponentModeler.json

@@ -9658,6 +9658,53 @@
       ],
       "type": "object"
     },
+    "LowFrequencySmoothingSpec": {
+      "additionalProperties": false,
+      "properties": {
+        "attrs": {
+          "default": {},
+          "type": "object"
+        },
+        "max_deviation": {
+          "default": 0.5,
+          "minimum": 0,
+          "type": "number"
+        },
+        "max_sampling_time": {
+          "default": 5.0,
+          "minimum": 0,
+          "type": "number"
+        },
+        "min_sampling_time": {
+          "default": 1.0,
+          "minimum": 0,
+          "type": "number"
+        },
+        "monitors": {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        },
+        "order": {
+          "default": 1,
+          "maximum": 3,
+          "minimum": 0,
+          "type": "integer"
+        },
+        "type": {
+          "default": "LowFrequencySmoothingSpec",
+          "enum": [
+            "LowFrequencySmoothingSpec"
+          ],
+          "type": "string"
+        }
+      },
+      "required": [
+        "monitors"
+      ],
+      "type": "object"
+    },
     "LumpedPort": {
       "additionalProperties": false,
       "properties": {
@@ -11484,6 +11531,44 @@
       },
       "type": "object"
     },
+    "ModelerLowFrequencySmoothingSpec": {
+      "additionalProperties": false,
+      "properties": {
+        "attrs": {
+          "default": {},
+          "type": "object"
+        },
+        "max_deviation": {
+          "default": 0.5,
+          "minimum": 0,
+          "type": "number"
+        },
+        "max_sampling_time": {
+          "default": 5.0,
+          "minimum": 0,
+          "type": "number"
+        },
+        "min_sampling_time": {
+          "default": 1.0,
+          "minimum": 0,
+          "type": "number"
+        },
+        "order": {
+          "default": 1,
+          "maximum": 3,
+          "minimum": 0,
+          "type": "integer"
+        },
+        "type": {
+          "default": "ModelerLowFrequencySmoothingSpec",
+          "enum": [
+            "ModelerLowFrequencySmoothingSpec"
+          ],
+          "type": "string"
+        }
+      },
+      "type": "object"
+    },
     "ModulationSpec": {
       "additionalProperties": false,
       "properties": {
@@ -14240,6 +14325,13 @@
           },
           "type": "array"
         },
+        "low_freq_smoothing": {
+          "allOf": [
+            {
+              "$ref": "#/definitions/LowFrequencySmoothingSpec"
+            }
+          ]
+        },
         "lumped_elements": {
           "default": [],
           "items": {
@@ -16922,6 +17014,21 @@
         }
       ]
     },
+    "low_freq_smoothing": {
+      "allOf": [
+        {
+          "$ref": "#/definitions/ModelerLowFrequencySmoothingSpec"
+        }
+      ],
+      "default": {
+        "attrs": {},
+        "max_deviation": 0.5,
+        "max_sampling_time": 5.0,
+        "min_sampling_time": 1.0,
+        "order": 1,
+        "type": "ModelerLowFrequencySmoothingSpec"
+      }
+    },
     "name": {
       "default": "",
       "type": "string"

tests/test_components/test_low_freq_smoothing.py

@@ -0,0 +1,50 @@
+"""Test low frequency smoothing specification."""
+
+from __future__ import annotations
+
+import pydantic.v1 as pydantic
+import pytest
+
+import tidy3d as td
+
+
+def test_low_freq_smoothing_spec_initialization_default_values():
+    """Test that LowFrequencySmoothingSpec initializes with correct default values."""
+    spec = td.LowFrequencySmoothingSpec(monitors=["monitor1"])
+    assert spec.min_sampling_time == 1
+    assert spec.max_sampling_time == 5
+    assert spec.order == 1
+    assert spec.max_deviation == 0.5
+
+
+def test_empty_monitors():
+    """Test that LowFrequencySmoothingSpec raises an error if monitors are not provided."""
+    with pytest.raises(pydantic.ValidationError):
+        td.LowFrequencySmoothingSpec(monitors=[])
+
+
+def test_monitors_exist():
+    """Test that LowFrequencySmoothingSpec raises an error if monitors do not exist."""
+    sim = td.Simulation(
+        size=(1, 1, 1),
+        monitors=[
+            td.ModeMonitor(
+                name="monitor1",
+                mode_spec=td.ModeSpec(num_modes=1),
+                freqs=[td.C_0],
+                size=(0.5, 0.5, 0),
+            )
+        ],
+        run_time=1e-12,
+        grid_spec=td.GridSpec.auto(min_steps_per_wvl=20, wavelength=1),
+        low_freq_smoothing=td.LowFrequencySmoothingSpec(monitors=["monitor1"]),
+    )
+
+    with pytest.raises(pydantic.ValidationError):
+        sim = td.Simulation(
+            size=(1, 1, 1),
+            monitors=[],
+            run_time=1e-12,
+            grid_spec=td.GridSpec.auto(min_steps_per_wvl=20, wavelength=1),
+            low_freq_smoothing=td.LowFrequencySmoothingSpec(monitors=["monitor1"]),
+        )

tests/test_plugins/smatrix/test_terminal_component_modeler.py

@@ -1424,3 +1424,115 @@ def test_wave_port_to_absorber(tmp_path):
     sim = list(modeler.sim_dict.values())[0]
     absorber = sim.internal_absorbers[0]
     assert absorber.boundary_spec == custom_boundary_spec
+
+
+def test_low_freq_smoothing_spec_initialization_default_values():
+    """Test that LowFrequencySmoothingSpec initializes with correct default values."""
+    from tidy3d.plugins.smatrix.component_modelers.terminal import ModelerLowFrequencySmoothingSpec
+
+    spec = ModelerLowFrequencySmoothingSpec()
+    assert spec.min_sampling_time == 1
+    assert spec.max_sampling_time == 5
+    assert spec.order == 1
+    assert spec.max_deviation == 0.5
+
+
+def test_low_freq_smoothing_spec_initialization_custom_values():
+    """Test that LowFrequencySmoothingSpec initializes with custom values."""
+    from tidy3d.plugins.smatrix.component_modelers.terminal import ModelerLowFrequencySmoothingSpec
+
+    spec = ModelerLowFrequencySmoothingSpec(
+        min_sampling_time=2, max_sampling_time=8, order=2, max_deviation=0.3
+    )
+    assert spec.min_sampling_time == 2
+    assert spec.max_sampling_time == 8
+    assert spec.order == 2
+    assert spec.max_deviation == 0.3
+
+
+def test_low_freq_smoothing_spec_edge_cases():
+    """Test edge cases and boundary conditions."""
+    from tidy3d.plugins.smatrix.component_modelers.terminal import ModelerLowFrequencySmoothingSpec
+
+    # Test with order 0 (constant fit)
+    spec = ModelerLowFrequencySmoothingSpec(order=0)
+    assert spec.order == 0
+
+    # Test with maximum order
+    spec = ModelerLowFrequencySmoothingSpec(order=3)
+    assert spec.order == 3
+
+    # Test with zero max_deviation
+    spec = ModelerLowFrequencySmoothingSpec(max_deviation=0.0)
+    assert spec.max_deviation == 0.0
+
+    # Test with maximum max_deviation
+    spec = ModelerLowFrequencySmoothingSpec(max_deviation=1.0)
+    assert spec.max_deviation == 1.0
+
+
+def test_low_freq_smoothing_spec_validation_sampling_times_invalid():
+    """Test validation of sampling time parameters."""
+    from tidy3d.plugins.smatrix.component_modelers.terminal import ModelerLowFrequencySmoothingSpec
+
+    # Test invalid range where min_sampling_time >= max_sampling_time
+    with pytest.raises(
+        ValueError, match="The minimum sampling time must be less than the maximum sampling time"
+    ):
+        ModelerLowFrequencySmoothingSpec(min_sampling_time=5, max_sampling_time=3)
+
+    with pytest.raises(
+        ValueError, match="The minimum sampling time must be less than the maximum sampling time"
+    ):
+        ModelerLowFrequencySmoothingSpec(min_sampling_time=3, max_sampling_time=3)
+
+
+def test_low_freq_smoothing_spec_validation_order_bounds():
+    """Test validation of order parameter bounds."""
+    from tidy3d.plugins.smatrix.component_modelers.terminal import ModelerLowFrequencySmoothingSpec
+
+    # Test valid orders
+    ModelerLowFrequencySmoothingSpec(order=0)
+    ModelerLowFrequencySmoothingSpec(order=3)
+
+    # Test invalid orders
+    with pytest.raises(pd.ValidationError):
+        ModelerLowFrequencySmoothingSpec(order=-1)
+
+    with pytest.raises(pd.ValidationError):
+        ModelerLowFrequencySmoothingSpec(order=4)
+
+
+def test_low_freq_smoothing_spec_validation_max_deviation_bounds():
+    """Test validation of max_deviation parameter bounds."""
+    from tidy3d.plugins.smatrix.component_modelers.terminal import ModelerLowFrequencySmoothingSpec
+
+    # Test valid max_deviation
+    ModelerLowFrequencySmoothingSpec(max_deviation=0.0)
+    ModelerLowFrequencySmoothingSpec(max_deviation=1.0)
+
+    # Test invalid max_deviation
+    with pytest.raises(pd.ValidationError):
+        ModelerLowFrequencySmoothingSpec(max_deviation=-0.1)
+
+
+def test_low_freq_smoothing_spec_sim_dict():
+    """Test that LowFrequencySmoothingSpec is correctly added to the sim_dict."""
+    from tidy3d.plugins.smatrix.component_modelers.terminal import ModelerLowFrequencySmoothingSpec
+
+    spec = ModelerLowFrequencySmoothingSpec(
+        min_sampling_time=2, max_sampling_time=8, order=2, max_deviation=0.3
+    )
+
+    modeler = make_coaxial_component_modeler(port_types=(WavePort, WavePort))
+    modeler = modeler.updated_copy(low_freq_smoothing=spec)
+    for sim in modeler.sim_dict.values():
+        assert spec.min_sampling_time == sim.low_freq_smoothing.min_sampling_time
+        assert spec.max_sampling_time == sim.low_freq_smoothing.max_sampling_time
+        assert spec.order == sim.low_freq_smoothing.order
+        assert spec.max_deviation == sim.low_freq_smoothing.max_deviation
+        assert sim.low_freq_smoothing.monitors == tuple(mnt.name for mnt in sim.monitors[-2:])
+
+    modeler = modeler.updated_copy(low_freq_smoothing=None)
+    for sim in modeler.sim_dict.values():
+        assert sim.low_freq_smoothing is None

tidy3d/__init__.py

@@ -4,6 +4,7 @@
 
 from tidy3d.components.boundary import BroadbandModeABCFitterParam, BroadbandModeABCSpec
 from tidy3d.components.data.index import SimulationDataMap
+from tidy3d.components.frequency_extrapolation import LowFrequencySmoothingSpec
 from tidy3d.components.index import SimulationMap
 from tidy3d.components.material.multi_physics import MultiPhysicsMedium
 from tidy3d.components.material.tcad.charge import (
@@ -619,6 +620,7 @@ def set_logging_level(level: str) -> None:
     "LinearLumpedElement",
     "Lorentz",
     "LossyMetalMedium",
+    "LowFrequencySmoothingSpec",
     "LumpedElement",
     "LumpedResistor",
     "Medium",