tidy3d.Medium

class Medium

Bases: AbstractMedium

Dispersionless medium. Mediums define the optical properties of the materials within the simulation.

Parameters:

• name (Attribute: name) –

  Type	Optional[str]
  Default	= None
  Description	Optional unique name for medium.

• frequency_range (Attribute: frequency_range) –

  Type	Optional[Tuple[float, float]]
  Default	= None
  Units	(Hz, Hz)
  Description	Optional range of validity for the medium.

• allow_gain (Attribute: allow_gain) –

  Type	bool
  Default	= False
  Description	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 (Attribute: nonlinear_spec) –

  Type	Union[NonlinearSpec, NonlinearSusceptibility]
  Default	= None
  Description	Nonlinear spec applied on top of the base medium properties.

• modulation_spec (Attribute: modulation_spec) –

  Type	Optional[ModulationSpec]
  Default	= None
  Description	Modulation spec applied on top of the base medium properties.

• heat_spec (Attribute: heat_spec) –

  Type	Union[FluidSpec, SolidSpec, NoneType]
  Default	= None
  Description	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.

• permittivity (Attribute: permittivity) –

  Type	ConstrainedFloatValue
  Default	= 1.0
  Units	None (relative permittivity)
  Description	Relative permittivity.

• conductivity (Attribute: conductivity) –

  Type	float
  Default	= 0.0
  Units	S/um
  Description	Electric conductivity. Defined such that the imaginary part of the complex permittivity at angular frequency omega is given by conductivity/omega.

Notes

In a dispersion-less medium, the displacement field \(D(t)\) reacts instantaneously to the applied electric field \(E(t)\).

\[D(t) = \epsilon E(t)\]

Example

>>> dielectric = Medium(permittivity=4.0, name='my_medium')
>>> eps = dielectric.eps_model(200e12)

See also

Notebooks

• Introduction on Tidy3D working principles

• Index

Lectures

• Modeling dispersive material in FDTD

GUI

• Mediums

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.

Methods

eps_model(frequency)	Complex-valued permittivity as a function of frequency.
from_nk(n, k, freq, **kwargs)	Convert n and k values at frequency freq to Medium.

permittivity

conductivity

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 dispersiveless medium, it equals sqrt(permittivity).

eps_model(frequency)

Complex-valued permittivity as a function of frequency.

classmethod from_nk(n, k, freq, **kwargs)

Convert n and k values at frequency freq to Medium.

Parameters:

• n (float) – Real part of refractive index.

• k (float = 0) – Imaginary part of refrative index.

• freq (float) – Frequency to evaluate permittivity at (Hz).

Returns:

medium containing the corresponding permittivity and conductivity.

Return type:

Medium

__hash__()

Hash method.