PerturbationPoleResidue

A dispersive medium described by the pole-residue pair model. It includes temperature and/or charge perturbation parameters, which allow users to convert between Heat/Charge and FDTD simulations. Charge response fields are part of the saved model; the editor offers this model from New Medium while editing a Heat simulation.

The frequency-dependence of the complex-valued permittivity is described by:

$\epsilon(\omega) = \epsilon_\infty - \sum_i\left[\frac{c_i}{j \omega + a_i} + \frac{c_i^\ast}{j \omega + a_i^\ast}\right]$

The medium panel separates Thermal Properties, Optical Properties, and Optical Perturbation. Additional supported medium settings are under Advanced.

Name

name: Optional unique name for the medium. The name appears in the Mediums list and is separate from the optical and thermal properties.

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

Subpixel

subpixel: If True and the simulation’s subpixel setting is also True, applies subpixel averaging to the perturbed medium.

Type: boolean

Default: True

Epsilon at Infinity

eps_inf: Relative permittivity at infinite frequency ($\epsilon_\infty$).

• Unit: unitless
• Constraint: greater than 0
• Default: 1

Poles

poles: List of complex-valued $(a_i, c_i)$ pole-residue pairs. Use Add Pole to add a pair; the editor displays the two values as a and c.

• Unit: rad/s
• Default: empty list

Optical Perturbation

Enable Optical Perturbation to expose the perturbation controls. Select one of the following representations:

• n/k (IndexPerturbation): Perturb the refractive-index and extinction-coefficient values. The panel can show dn/dT (Refractive Index Perturbation) and dk/dT (Extinction Coefficient Perturbation), together with the wavelength or frequency where the coefficients apply.
• ε/σ (PermittivityPerturbation): Perturb the permittivity and conductivity directly.

perturbation_spec: Selects the n/k or ε/σ representation above.

eps_inf_perturbation: Optional ParameterPerturbation for the permittivity at infinity.

poles_perturbation: Optional ParameterPerturbation pair for the a and c values of each pole.

The perturbation controls also provide a reference temperature and a valid temperature range. A parameter perturbation can contain a heat response, a charge response, or both.

Advanced

Advanced can contain the frequency range, Allow_gain, and Space-Time Modulation. Nonlinearity Specification is not available for perturbation media.

Appearance

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