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import unittest
import meep as mp
# compute group velocity of a waveguide mode using two different methods
# (1) ratio of Poynting flux to energy density
# (2) via MPB from get-eigenmode-coefficients
class TestDftEnergy(unittest.TestCase):
def test_dft_energy(self):
resolution = 20
cell = mp.Vector3(10, 5)
geom = [
mp.Block(size=mp.Vector3(mp.inf, 1, mp.inf), material=mp.Medium(epsilon=12))
]
pml = [mp.PML(1)]
fsrc = 0.15
sources = [
mp.EigenModeSource(
src=mp.GaussianSource(frequency=fsrc, fwidth=0.2 * fsrc),
center=mp.Vector3(-3),
size=mp.Vector3(y=5),
eig_band=1,
eig_parity=mp.ODD_Z + mp.EVEN_Y,
eig_match_freq=True,
)
]
sim = mp.Simulation(
resolution=resolution,
cell_size=cell,
geometry=geom,
boundary_layers=pml,
sources=sources,
symmetries=[mp.Mirror(direction=mp.Y)],
)
flux = sim.add_flux(
fsrc,
0,
1,
mp.FluxRegion(center=mp.Vector3(3), size=mp.Vector3(y=5)),
decimation_factor=1,
)
energy = sim.add_energy(
fsrc,
0,
1,
mp.EnergyRegion(center=mp.Vector3(3), size=mp.Vector3(y=5)),
decimation_factor=1,
)
energy_decimated = sim.add_energy(
fsrc,
0,
1,
mp.EnergyRegion(center=mp.Vector3(3), size=mp.Vector3(y=5)),
decimation_factor=10,
)
sim.run(until_after_sources=100)
res = sim.get_eigenmode_coefficients(flux, [1], eig_parity=mp.ODD_Z + mp.EVEN_Y)
mode_vg = res.vgrp[0]
poynting_flux = mp.get_fluxes(flux)[0]
e_energy = mp.get_electric_energy(energy)[0]
ratio_vg = (0.5 * poynting_flux) / e_energy
m_energy = mp.get_magnetic_energy(energy)[0]
t_energy = mp.get_total_energy(energy)[0]
self.assertAlmostEqual(m_energy + e_energy, t_energy)
self.assertAlmostEqual(ratio_vg, mode_vg, places=3)
e_energy_decimated = mp.get_electric_energy(energy_decimated)[0]
m_energy_decimated = mp.get_magnetic_energy(energy_decimated)[0]
self.assertAlmostEqual(e_energy, e_energy_decimated, places=1)
self.assertAlmostEqual(m_energy, m_energy_decimated, places=1)
if __name__ == "__main__":
unittest.main()
|
