Meep integration: automatically use effective refractive index

[HelgeGehring]

Using the function calculate_effective_permittivity introduced in #501 3D simulations can be reduced to 2D simulations.
How would we best integrate it into the meep-plugin to set it automatically?

from gdsfactory.components import mmi1x2
from gdsfactory.simulation.gmeep import write_sparameters_meep
from gdsfactory.simulation.effective_permittivity import calculate_effective_permittivity

mmi = mmi1x2(width_mmi=5, length_mmi=10, gap_mmi=1, length_taper=2)
mmi.show()
material_name_to_meep = {
    'si': float(calculate_effective_permittivity(3.477 ** 2, 1.444 ** 2, 1.444 ** 2, .22, 1.55, 'te')[0] ** .5)}
write_sparameters_meep(mmi, resolution=20, is_3d=False, animate=True, material_name_to_meep=material_name_to_meep)

[joamatab]

Hi Helge,

yes, i like it, it's very simple and functional :)

I think material_name_to_meep maps LayerStack layer names to refractive index (not permitivity). I also made some changes to be more consistent in this branch

let me know what you think

[HelgeGehring]

Looks good!

[joamatab]

awesome! I will merge it and then work on an example on the notebooks :)

this looks great Helge! now we can do 2.5D FDTD simulations 🎉