# CustomSellmeier

A spatially varying dispersive medium described by the Sellmeier model. The frequency-dependence of the refractive index is described by:

n(λ)2=1+∑iBiλ2λ2−Cin(\lambda)^2 = 1 + \sum_i \frac{B_i \lambda^2}{\lambda^2 - C_i}

# Name

name: Optional unique name for the medium.

# Thermal Properties

This section appears when the task group includes a Heat solver and is omitted from a standalone FDTD task.

# Medium Type

type: Selects the thermal model under Medium Type.

Type: string

Options:

  • FluidSpec: The Heat solver does not solve for temperature in regions that use this medium.
  • SolidSpec: The Heat solver uses the solid thermal model.

Default: SolidSpec for a new medium in a Heat simulation.

# Thermal Conductivity

conductivity: Thermal conductivity. This field is shown when Medium Type is SolidSpec.

Type: floating-point number

  • Unit: W/(μm·K)
  • Constraint: greater than 0
  • Required field

NOTE

The editor has no inputs for heat capacity (capacity) or density (density). When you create a medium in a Heat simulation, the editor sets capacity to 1. To set other values, use the Python interface. See Thermal Properties for the API fields.

# Optical Properties

# Interpolation Method

interp_method: Interpolation method to obtain permittivity values that are not supplied at the Yee grids.

For grids outside the range of the supplied data, extrapolation will be applied. When the extrapolated value is smaller (greater) than the minimal (maximal) of the supplied data, the extrapolated value will take the minimal (maximal) of the supplied data.

Options:

  • nearest
  • linear

Default: nearest

# Subpixel

subpixel: If True and simulation’s subpixel is also True, applies subpixel averaging of the permittivity on the interface of the structure, including exterior boundary and intersection interfaces with other structures.

Type: boolean

Default: False

# Coefficients

coeffs: List of Sellmeier (Bi,CiB_i, C_i) coefficients. Click the Import Material button to load the coefficient dataset.

If you prepare the upload outside the editor, create the corresponding medium with the Python interface and call to_hdf5(filename) (opens new window) to write the expected HDF5 dataset structure. For a spatially varying medium, see the Custom Medium tutorial (opens new window).

Type: SpatialDataArray

BB: floating-point number

  • Unit: unitless

CC: floating-point number

  • Unit: μm²
  • Constraint: greater than or equal to 0

# Advanced

frequency_range: Optional lower and upper frequency bounds for the medium.

Type: pair of floating-point numbers

  • Unit: Hz for both values
  • Constraint: each value greater than 0
  • Default: None

# Allow Gain

allow_gain: Enable gain medium. Caution: simulations with gain medium are unstable and are likely to diverge. Simulations with this option enabled are still charged even if they diverge. Monitor data up to the divergence point is still returned and can be useful in some cases.

Type: boolean

Default: False

# Appearance

Appearance settings control the medium’s face color and transparency in the model view. They do not change the optical properties.

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