FAQ for anisotropic medium

_faqs/how-do-i-use-anisotropic-medium.md

@@ -0,0 +1,38 @@
+---
+title: How Do I Use Anisotropic Medium?
+date: 2025-09-24 11:50:54
+enabled: true
+category: "Inverse Design"
+---
+Currently, classes of [AnisotropicMedium](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.AnisotropicMedium.html){: .color-primary-hover} are not supported with the `autograd` plugin.  
+However, it is possible to work with diagonally anisotropic materials by defining a [CustomMedium](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.CustomMedium.html#tidy3d.CustomMedium){: .color-primary-hover} that uses a diagonally anisotropic [PermittivityDataset](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.PermittivityDataset.html){: .color-primary-hover}.
+
+The following example shows how to create an anisotropic LN medium with the extraordinary axis aligned along the z-axis:
+
+
+<div markdown class="code-snippet">
+{% highlight python %}
+# Define the coordinates for the medium
+X = [-1e12, 1e12]
+f = [td.C_0]
+coords = dict(x=X, y=X, z=X, f=f)
+
+# Define the datasets
+n_e = 2.17
+n_o = 2.23
+
+eps_xx = td.ScalarFieldDataArray(np.ones((2, 2, 2, 1)) * n_e**2, coords=coords)
+eps_yy = eps_xx
+eps_zz = td.ScalarFieldDataArray(np.ones((2, 2, 2, 1)) * n_o**2, coords=coords)
+
+# Define anisotropic permittivity dataset
+permittivity = td.PermittivityDataset(
+    eps_xx=eps_xx,
+    eps_yy=eps_yy,
+    eps_zz=eps_zz
+)
+
+# Define anisotropic custom medium
+medium = td.CustomMedium(eps_dataset=permittivity)
+{% endhighlight %}
+{% include copy-button.html %}</div>

docs/faq/how-do-i-use-anisotropic-medium.md

@@ -0,0 +1,41 @@
+# How Do I Use Anisotropic Medium?
+
+| Date       | Category    |
+|------------|-------------|
+| 2025-09-24 11:50:54 | Inverse Design |
+
+
+Currently, classes of [AnisotropicMedium](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.AnisotropicMedium.html) are not supported with the `autograd` plugin.  
+However, it is possible to work with diagonally anisotropic materials by defining a [CustomMedium](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.CustomMedium.html#tidy3d.CustomMedium) that uses a diagonally anisotropic [PermittivityDataset](https://docs.flexcompute.com/projects/tidy3d/en/latest/api/_autosummary/tidy3d.PermittivityDataset.html).
+
+The following example shows how to create an anisotropic LN medium with the extraordinary axis aligned along the z-axis:
+
+
+
+
+```python
+# Define the coordinates for the medium
+X = [-1e12, 1e12]
+f = [td.C_0]
+coords = dict(x=X, y=X, z=X, f=f)
+
+# Define the datasets
+n_e = 2.17
+n_o = 2.23
+
+eps_xx = td.ScalarFieldDataArray(np.ones((2, 2, 2, 1)) * n_e**2, coords=coords)
+eps_yy = eps_xx
+eps_zz = td.ScalarFieldDataArray(np.ones((2, 2, 2, 1)) * n_o**2, coords=coords)
+
+# Define anisotropic permittivity dataset
+permittivity = td.PermittivityDataset(
+    eps_xx=eps_xx,
+    eps_yy=eps_yy,
+    eps_zz=eps_zz
+)
+
+# Define anisotropic custom medium
+medium = td.CustomMedium(eps_dataset=permittivity)
+```
+
+

docs/inverse-design.rst

@@ -16,3 +16,4 @@ Inverse Design
    faq/how-do-i-include-fabrication-constraints-in-adjoint-topology-optimization.md
    faq/how-do-i-include-fabrication-constraints-in-adjoint-level-set-optimization.md
    faq/how-do-i-export-the-final-inverse-design-structure-to-gds.md
+   faq/how-do-i-use-anisotropic-medium.md

faq_categories.json

@@ -300,7 +300,8 @@
       "_faqs/how-do-i-include-fabrication-constraints-in-adjoint-shape-optimization.md",
       "_faqs/how-do-i-include-fabrication-constraints-in-adjoint-topology-optimization.md",
       "_faqs/how-do-i-include-fabrication-constraints-in-adjoint-level-set-optimization.md",
-      "_faqs/how-do-i-export-the-final-inverse-design-structure-to-gds.md"
+      "_faqs/how-do-i-export-the-final-inverse-design-structure-to-gds.md",
+      "_faqs/how-do-i-use-anisotropic-medium.md"
     ]
   },
   {