Class EigenModeSource

python/source.py:409–690

This is a subclass of `Source` and has **all of the properties** of `Source` above. However, you normally do not specify a `component`. Instead of `component`, the current source components and amplitude profile are computed by calling MPB to compute the modes, $\\mathbf{u}_{n,\\mat

class EigenModeSource(Source):
    """
    This is a subclass of `Source` and has **all of the properties** of `Source` above.
    However, you normally do not specify a `component`. Instead of `component`, the
    current source components and amplitude profile are computed by calling MPB to compute
    the modes, $\\mathbf{u}_{n,\\mathbf{k}}(\\mathbf{r}) e^{i \\mathbf{k} \\cdot \\mathbf{r}}$,
    of the dielectric profile in the region given by the `size` and `center` of the
    source, with the modes computed as if the *source region were repeated periodically in
    all directions*. If an `amplitude` and/or `amp_func` are supplied, they are
    *multiplied* by this current profile. The desired eigenmode and other features are
    specified by the properties shown in `__init__`.

    Eigenmode sources are normalized so that in the case of a time-harmonic simulation
    with all sources and fields having monochromatic time dependence $e^{-i 2\\pi f_m t}$
    where $f_m$ is the frequency of the eigenmode, the total time-average power of the
    fields — the integral of the normal Poynting vector over the entire cross-sectional
    line or plane — is equal to 1. This convention has two use cases:

    + For [frequency-domain
      calculations](Python_User_Interface.md#frequency-domain-solver) involving a
      `ContinuousSource` time dependence, the time-average power of the fields is 1.

    + For time-domain calculations involving a time dependence $W(t)$ which is typically a
      [Gaussian](#gaussiansource), the amplitude of the fields at frequency $f$ will be
      multiplied by $\\widetilde W(f)$, the Fourier transform of $W(t)$, while
      field-bilinear quantities like the [Poynting flux](#flux-spectra) and [energy
      density](#energy-density-spectra) are multiplied by $|\\widetilde W(f)|^2$. For the
      particular case of a Gaussian time dependence, the Fourier transform at $f$ can be
      obtained via the `fourier_transform` class method.

    In either case, the `eig_power` method returns the total power at frequency `f`.
    However, for a user-defined [`CustomSource`](#customsource), `eig_power` will *not*
    include the $|\\widetilde W(f)|^2$ factor since Meep does not know the Fourier
    transform of your source function $W(t)$. You will have to multiply by this yourself
    if you need it.

    **Note:** Due to discretization effects, the normalization of eigenmode sources to
    yield unit power transmission is only approximate: at any finite resolution, the power
    of the fields as measured using [DFT flux](#flux-spectra) monitors will not precisely
    match that of calling `eig_power` but will rather include discretization errors that
    decrease with resolution.  Generally, the most reliable procedure is to normalize your
    calculations by the power computed in a separate normalization run at the same
    resolution, as shown in several of the tutorial examples.

    Note that Meep's MPB interface only supports dispersionless non-magnetic materials but
    it does support anisotropic $\\varepsilon$. Any nonlinearities, magnetic responses $\\mu$,
    conductivities $\\sigma$, or dispersive polarizations in your materials will be *ignored* when
    computing the eigenmode source. PML will also be ignored.

    The `SourceTime` object (`Source.src`), which specifies the time dependence of the
    source, can be one of `ContinuousSource`, `GaussianSource` or `CustomSource`.
    """

    def __init__(
        self,
        src,
        center=None,
        volume=None,