feat: add Nunley variant to germanium material library

- Add Ge_Nunley variant based on Nunley et al. 2016 data
- 20-pole fit with RMS error of 0.0132
- Valid wavelength range: 0.188 - 2.480 μm
- Add reference: Nunley2015 (J. Vac. Sci. Technol. B 34, 061205)

Author: yaugenst-flex

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - Add support for `np.unwrap` in `tidy3d.plugins.autograd`.
+- Add Nunley variant to germanium material library based on Nunley et al. 2016 data.
 
 ### Fixed
 - Arrow lengths are now scaled consistently in the X and Y directions, and their lengths no longer exceed the height of the plot window.

tidy3d/material_library/material_library.py

@@ -1005,6 +1005,43 @@ def medium(self, optical_axis: Axis):
     reference=[material_refs["Palik_Lossy"]],
 )
 
+Ge_Nunley = VariantItem(
+    medium=PoleResidue(
+        name="Ge_Nunley",
+        eps_inf=1.0,
+        poles=[
+            (
+                (-1055692444928990.6 - 1.2069979211686232e16j),
+                (1107423663161164.6 - 3093285987380348.5j),
+            ),
+            ((-3216853350289244 - 8291440266759688j), (5700802820282152 + 2.5732993737266788e16j)),
+            ((-541881030908034.7 - 8791646324216410j), (-937105384931749 + 541020934229084.2j)),
+            (
+                (-976547995477318.4 - 6543303598934721j),
+                (-1.0737211590127532e16 + 1.3992511131747758e16j),
+            ),
+            ((-284492778464386.2 - 6696785988114651j), (-2168480500787241.8 - 696493506373301.2j)),
+            ((-900354155072.7748 - 6663372533420019j), (183103725786.0085 - 141583942490.17123j)),
+            ((-7073535582440.927 - 6580195498223051j), (262790152.22284198 + 378843848585.63043j)),
+            ((-270911770733075.62 - 6447924271229311j), (1207997886295188 + 1471602437337227.5j)),
+            ((-255993466255361.62 - 5008805217676040j), (445613879952076.8 - 223801118798973.3j)),
+            ((-344512832764646.75 - 4858405095425429j), (563341672141455.9 + 1286782730502855.5j)),
+            ((-695769101918184.8 - 3620945512916543j), (5328924572609390 + 5529617018233712j)),
+            ((-252629750588162 - 3513125220372237.5j), (109779730682375.69 + 2230058891609707j)),
+            (
+                (-141325408476762.66 - 3230461058493017.5j),
+                (126429312165475.8 + 1257642646101307.8j),
+            ),
+            ((-498950664609906.4 - 1179396998903782.5j), (180816169912939.7 - 297981189005482.4j)),
+            ((-37573278339073.01 - 1213096851555221.8j), (13359584691343.223 - 3071910249946.702j)),
+            ((-99651215401004 - 1635758773069449.5j), (5479484262079.737 - 6773804202146.6045j)),
+        ],
+        frequency_range=(1.209e14, 1.595e15),
+    ),
+    reference=[material_refs["Nunley2016"]],
+    data_url="https://refractiveindex.info/data_csv.php?datafile=database/data/main/Ge/nk/Nunley.yml",
+)
+
 GeOx_Horiba = VariantItem(
     medium=PoleResidue(
         name="GeOx_Horiba",
@@ -2224,6 +2261,7 @@ def _repr_pretty_(self, p, cycle):
             "Palik_Lossless": Ge_Palik_Lossless,
             "Palik_Lossy": Ge_Palik_Lossy,
             "Icenogle1976": Ge_Icenogle1976,
+            "Nunley": Ge_Nunley,
         },
         default="Icenogle1976",
     ),

tidy3d/material_library/material_reference.py

@@ -112,6 +112,13 @@ class ReferenceData(Tidy3dBaseModel):
         "for germanium J. Opt. Soc. Am. 69 178-180 (1979)",
         doi="https://doi.org/10.1364/JOSA.69.000178",
     ),
+    "Nunley2016": ReferenceData(
+        journal="T. S. Nunley, N. S. Fernando, N. Samarasingha, J. M. Moya, "
+        "C. M. Nelson, A. A. Medina, and S. Zollner. Optical constants of "
+        "germanium and thermally grown germanium dioxide from 0.5 to 6.6eV "
+        "via a multisample ellipsometry investigation, J. Vac. Sci. Technol. B 34, 061205 (2016)",
+        doi="https://doi.org/10.1116/1.4963075",
+    ),
     "Pettit1965": ReferenceData(
         journal="G. D. Pettit and W. J. Turner. Refractive index of InP, "
         "J. Appl. Phys. 36, 2081 (1965)",