MaterialDB

compass.materials.database.MaterialDB is the central registry for optical material properties. It provides wavelength-dependent refractive index $(n, k)$ and complex permittivity $ε$ for all materials used in simulations.

Interactive Material Optical Properties

Select a material to view its refractive index (n) and extinction coefficient (k) across the visible spectrum.

Material:

Constructor

python

class MaterialDB:
    def __init__(self, db_path: Optional[str] = None):

Parameters:

db_path -- Path to directory containing CSV material files. Defaults to the materials/ directory at the project root.

On construction, MaterialDB automatically:

Registers built-in constant and analytic materials (air, polymers, dielectrics)
Loads tabulated CSV data from the materials directory (silicon, tungsten, color filters)
Falls back to approximate built-in data if CSV files are missing

Querying methods

`get_nk`

python

def get_nk(self, name: str, wavelength: float) -> Tuple[float, float]:

Returns (n, k) -- real and imaginary parts of the refractive index -- at the given wavelength (in um).

Raises: KeyError if the material is not registered.

`get_epsilon`

python

def get_epsilon(self, name: str, wavelength: float) -> complex:

Returns complex permittivity $ε = (n + i k)^{2}$ at the given wavelength.

`get_epsilon_spectrum`

python

def get_epsilon_spectrum(self, name: str, wavelengths: np.ndarray) -> np.ndarray:

Returns an array of complex permittivity values over a wavelength array.

`list_materials`

python

def list_materials(self) -> List[str]:

Returns a sorted list of all registered material names.

`has_material`

python

def has_material(self, name: str) -> bool:

Returns True if the material exists in the database.

Registration methods

`register_constant`

python

def register_constant(self, name: str, n: float, k: float = 0.0) -> None:

python

db.register_constant("my_glass", n=1.52, k=0.0)

`register_cauchy`

python

def register_cauchy(self, name: str, A: float, B: float = 0.0, C: float = 0.0) -> None:

n (λ) = A + \frac{B}{λ^{2}} + \frac{C}{λ^{4}}

where $λ$ is in um. The extinction coefficient $k$ is zero (non-absorbing).

python

db.register_cauchy("polymer", A=1.56, B=0.004, C=0.0)

`register_sellmeier`

python

def register_sellmeier(self, name: str, B: List[float], C: List[float]) -> None:

n^{2} (λ) = 1 + \sum_{i} \frac{B_{i} λ^{2}}{λ^{2} - C_{i}}

python

db.register_sellmeier(
    "sio2",
    B=[0.6961663, 0.4079426, 0.8974794],
    C=[0.0684043**2, 0.1162414**2, 9.896161**2],
)

`load_csv`

python

def load_csv(self, name: str, filepath: str, interpolation: str = "cubic_spline") -> None:

Load tabulated material data from a CSV file. The CSV format is:

# wavelength(um), n, k
0.400, 5.381, 0.340
0.410, 5.253, 0.296
...

Lines starting with # are treated as comments. Data is automatically sorted by wavelength. Interpolation uses cubic splines (requires >= 4 data points) or linear interpolation as fallback.

Parameters:

name -- Material name for registration.
filepath -- Path to CSV file.
interpolation -- "cubic_spline" (default) or "linear".

Built-in materials

Core materials

Name	Type	Model	Typical n	Typical k
`air`	Constant	n=1.0, k=0.0	1.0	0.0
`polymer_n1p56`	Cauchy	A=1.56, B=0.004	1.56	0.0
`sio2`	Sellmeier	3-term	1.46	0.0
`si3n4`	Sellmeier	2-term	2.0	0.0
`hfo2`	Cauchy	A=1.90, B=0.02	1.90	0.0
`tio2`	Cauchy	A=2.27, B=0.05	2.27	0.0
`silicon`	Tabulated	Green 2008	3.5-5.6	0.003-3.0
`tungsten`	Tabulated	Approximate	3.4-3.7	2.7-3.4
`cf_red`	Tabulated	Lorentzian	1.55	0-0.15
`cf_green`	Tabulated	Lorentzian	1.55	0-0.12
`cf_blue`	Tabulated	Lorentzian	1.55	0-0.18

Metals

Tabulated optical constants for metals commonly used in CIS interconnects, metal grids, and plasmonic structures. Wavelength range: 300--1100 nm.

Name	Formula	Source	Typical n (550nm)	Typical k (550nm)
`aluminum`	Al	Rakic 1998	0.58	5.52
`gold`	Au	Johnson & Christy 1972	0.17	3.29
`silver`	Ag	Johnson & Christy 1972	0.07	4.39
`copper`	Cu	Johnson & Christy 1972	0.53	1.74
`titanium`	Ti	Johnson & Christy 1974	2.37	3.30
`titanium_nitride`	TiN	Patsalas 2003	1.31	2.31

Dielectrics

Tabulated optical constants for dielectric films used in antireflection coatings (ARC), passivation, and transparent conductors.

Name	Formula	Source	Typical n (550nm)
`silicon_nitride`	Si3N4	Philipp 1973	2.02
`aluminum_oxide`	Al2O3	Malitson 1962	1.77
`tantalum_pentoxide`	Ta2O5	Bright 2012	2.11
`magnesium_fluoride`	MgF2	Dodge 1984	1.38
`zinc_oxide`	ZnO	Bond 1965	2.07
`indium_tin_oxide`	ITO	Konig 2014	1.95
`silicon_oxynitride`	SiON	Approximate	1.70

Polymers

Tabulated optical constants for polymer materials used in microlenses, planarization layers, and photoresists.

Name	Formula	Source	Typical n (550nm)
`pmma`	PMMA	Sultanova 2009	1.49
`polycarbonate`	PC	Sultanova 2009	1.58
`polyimide`	PI	Birkholz 2000	1.70
`benzocyclobutene`	BCB	Dow Chemical	1.54
`su8`	SU-8	MicroChem	1.59

Semiconductors

Tabulated optical constants for semiconductor materials beyond silicon, for NIR and III-V sensor modeling.

Name	Formula	Source	Typical n (550nm)	Typical k (550nm)
`germanium`	Ge	Aspnes 1983	4.04	0.36
`gallium_arsenide`	GaAs	Aspnes 1983	3.98	0.17
`indium_phosphide`	InP	Aspnes 1983	3.70	0.17

MaterialData

The internal data container for each material:

python

@dataclass
class MaterialData:
    name: str
    mat_type: Literal["constant", "tabulated", "cauchy", "sellmeier"]
    n_const: float = 1.0
    k_const: float = 0.0
    wavelengths: Optional[np.ndarray] = None
    n_data: Optional[np.ndarray] = None
    k_data: Optional[np.ndarray] = None
    interpolation: str = "cubic_spline"
    cauchy_A: float = 1.0
    cauchy_B: float = 0.0
    cauchy_C: float = 0.0
    sellmeier_B: Optional[List[float]] = None
    sellmeier_C: Optional[List[float]] = None

`MaterialData.get_nk(wavelength) -> Tuple[float, float]`

Returns (n, k) using the appropriate dispersion model.

`MaterialData.get_epsilon(wavelength) -> complex`

Returns $ε = (n + i k)^{2}$ .

CSV auto-loading

On construction, MaterialDB looks for CSV files in the materials directory using these filename mappings:

Core materials (top-level directory):

Material name	Expected filenames
`silicon`	`silicon_green2008.csv`, `silicon_palik.csv`
`tungsten`	`tungsten.csv`
`cf_red`	`color_filter_red.csv`
`cf_green`	`color_filter_green.csv`
`cf_blue`	`color_filter_blue.csv`

If a CSV file is found, it is loaded automatically. Otherwise, a built-in approximation is used.

Extended materials (categorized subdirectories):

Subdirectory	Materials
`metals/`	`aluminum.csv`, `gold.csv`, `silver.csv`, `copper.csv`, `titanium.csv`, `titanium_nitride.csv`
`dielectrics/`	`silicon_nitride.csv`, `aluminum_oxide.csv`, `tantalum_pentoxide.csv`, `magnesium_fluoride.csv`, `zinc_oxide.csv`, `indium_tin_oxide.csv`, `silicon_oxynitride.csv`
`polymers/`	`pmma.csv`, `polycarbonate.csv`, `polyimide.csv`, `benzocyclobutene.csv`, `su8.csv`
`semiconductors/`	`germanium.csv`, `gallium_arsenide.csv`, `indium_phosphide.csv`

Extended material CSV files are optional. If a file is missing, the corresponding material is simply not registered (no fallback).

MaterialDB ​

Interactive Material Optical Properties

Constructor ​

Querying methods ​

get_nk ​

get_epsilon ​

get_epsilon_spectrum ​

list_materials ​

has_material ​

Registration methods ​

register_constant ​

register_cauchy ​

register_sellmeier ​

load_csv ​

Built-in materials ​

Core materials ​

Metals ​

Dielectrics ​

Polymers ​

Semiconductors ​

MaterialData ​

MaterialData.get_nk(wavelength) -> Tuple[float, float] ​

MaterialData.get_epsilon(wavelength) -> complex ​

CSV auto-loading ​

MaterialDB

Constructor

Querying methods

`get_nk`

`get_epsilon`

`get_epsilon_spectrum`

`list_materials`

`has_material`

Registration methods

`register_constant`

`register_cauchy`

`register_sellmeier`

`load_csv`

Built-in materials

Core materials

Metals

Dielectrics

Polymers

Semiconductors

MaterialData

`MaterialData.get_nk(wavelength) -> Tuple[float, float]`

`MaterialData.get_epsilon(wavelength) -> complex`

CSV auto-loading