tidy3d.NonlinearSusceptibility

class NonlinearSusceptibility

Bases: NonlinearModel

Model for an instantaneous nonlinear chi3 susceptibility. The expression for the instantaneous nonlinear polarization is given below.

Parameters:

• chi3 (Attribute: chi3) –

  Type	float
  Default	= 0
  Units	um^2 / V^2
  Description	Chi3 nonlinear susceptibility.

• numiters (Attribute: numiters) –

  Type	Optional[PositiveInt]
  Default	= None
  Description	Deprecated. The old usage ‘nonlinear_spec=model’ with ‘model.numiters’ is deprecated and will be removed in a future release. The new usage is ‘nonlinear_spec=NonlinearSpec(models=[model], num_iters=num_iters)’. Under the new usage, this parameter is ignored, and ‘NonlinearSpec.num_iters’ is used instead.

Notes

This model uses real time-domain fields, so \(\chi_3\) must be real.

\[P_{NL} = \varepsilon_0 \chi_3 |E|^2 E\]

The nonlinear constitutive relation is solved iteratively; it may not converge for strong nonlinearities. Increasing tidy3d.NonlinearSpec.numiters can help with convergence.

For complex fields (e.g. when using Bloch boundary conditions), the nonlinearity is applied separately to the real and imaginary parts, so that the above equation holds when both \(E\) and \(P_{NL}\) are replaced by their real or imaginary parts. The nonlinearity is only applied to the real-valued fields since they are the physical fields.

Different field components do not interact nonlinearly. For example, when calculating \(P_{NL, x}\), we approximate \(|E|^2 \approx |E_x|^2\). This approximation is valid when the \(E\) field is predominantly polarized along one of the x, y, or z axes.

Example

>>> nonlinear_susceptibility = NonlinearSusceptibility(chi3=1)

Attributes

complex_fields

Whether the model uses complex fields.

Methods

chi3

numiters

property complex_fields

Whether the model uses complex fields.

__hash__()

Hash method.