tidy3d.components.medium.DispersiveMedium

class DispersiveMedium

Bases: AbstractMedium, ABC

A Medium with dispersion: field propagation characteristics depend on frequency.

Parameters:

• name (Optional[str] = None) – Optional unique name for medium.

• frequency_range (Optional[Tuple[float, float]] = None) – [units = (Hz, Hz)]. Optional range of validity for the medium.

• allow_gain (bool = False) – Allow the medium to be active. Caution: simulations with a gain medium are unstable, and are likely to diverge.Simulations where ‘allow_gain’ is set to ‘True’ will still be charged even if diverged. Monitor data up to the divergence point will still be returned and can be useful in some cases.

• nonlinear_spec (Union[NonlinearSpec, NonlinearSusceptibility] = None) – Nonlinear spec applied on top of the base medium properties.

• modulation_spec (Optional[ModulationSpec] = None) – Modulation spec applied on top of the base medium properties.

• heat_spec (Union[FluidSpec, SolidSpec, NoneType] = None) – Specification of the medium heat properties. They are used for solving the heat equation via the HeatSimulation interface. Such simulations can be used for investigating the influence of heat propagation on the properties of optical systems. Once the temperature distribution in the system is found using HeatSimulation object, Simulation.perturbed_mediums_copy() can be used to convert mediums with perturbation models defined into spatially dependent custom mediums. Otherwise, the heat_spec does not directly affect the running of an optical Simulation.

Notes

In dispersive mediums, the displacement field \(D(t)\) depends on the previous electric field \(E( t')\) and time-dependent permittivity \(\epsilon\) changes.

\[D(t) = \int \epsilon(t - t') E(t') \delta t'\]

Dispersive mediums can be defined in three ways:

• Imported from our material library.

• Defined directly by specifying the parameters in the various supplied dispersive models.

• Fitted to optical n-k data using the dispersion fitting tool plugin.

It is important to keep in mind that dispersive materials are inevitably slower to simulate than their dispersion-less counterparts, with complexity increasing with the number of poles included in the dispersion model. For simulations with a narrow range of frequencies of interest, it may sometimes be faster to define the material through its real and imaginary refractive index at the center frequency.

See also

CustomPoleResidue:

A spatially varying dispersive medium described by the pole-residue pair model.

Notebooks

• Fitting dispersive material models

Lectures

• Modeling dispersive material in FDTD

Attributes

n_cfl	This property computes the index of refraction related to CFL condition, so that the FDTD with this medium is stable when the time step size that doesn't take material factor into account is multiplied by n_cfl.
pole_residue	Representation of Medium as a pole-residue model.

Methods

complex_to_tuple(value)	Convert a complex number to a tuple of real and imaginary parts.
tuple_to_complex(value)	Convert a tuple of real and imaginary parts to complex number.

property pole_residue

Representation of Medium as a pole-residue model.

property n_cfl

This property computes the index of refraction related to CFL condition, so that the FDTD with this medium is stable when the time step size that doesn’t take material factor into account is multiplied by n_cfl.

For PoleResidue model, it equals sqrt(eps_inf) [https://ieeexplore.ieee.org/document/9082879].

static tuple_to_complex(value)

Convert a tuple of real and imaginary parts to complex number.

static complex_to_tuple(value)

Convert a complex number to a tuple of real and imaginary parts.

__hash__()

Hash method.