tidy3d.Medium

class Medium

Bases: AbstractMedium

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

Parameters:

• attrs (dict = {}) – Dictionary storing arbitrary metadata for a Tidy3D object. This dictionary can be freely used by the user for storing data without affecting the operation of Tidy3D as it is not used internally. Note that, unlike regular Tidy3D fields, attrs are mutable. For example, the following is allowed for setting an attr obj.attrs['foo'] = bar. Also note that Tidy3D` will raise a TypeError if attrs contain objects that can not be serialized. One can check if attrs are serializable by calling obj.json().

• 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.

• permittivity (ConstrainedFloatValue = 1.0) – [units = None (relative permittivity)]. Relative permittivity.

• conductivity (float = 0.0) – [units = S/um]. 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.
attrs

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.

Inherited Common Usage

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.