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import math
import unittest
import numpy as np
import meep as mp
class TestGaussianBeamSource(unittest.TestCase):
def gaussian_beam(self, rot_angle):
s = 14
resolution = 25
dpml = 2
cell_size = mp.Vector3(s, s)
boundary_layers = [mp.PML(thickness=dpml)]
beam_x0 = mp.Vector3(0, 7.0) # beam focus (relative to source center)
beam_kdir = mp.Vector3(0, 1, 0).rotate(
mp.Vector3(0, 0, 1), math.radians(rot_angle)
) # beam propagation direction
beam_w0 = 0.8 # beam waist radius
beam_E0 = mp.Vector3(0, 0, 1)
beam_x0 = beam_x0.rotate(mp.Vector3(0, 0, 1), math.radians(rot_angle))
fcen = 1
src_x = 0
src_y = -0.5 * s + dpml + 1.0
sources = [
mp.GaussianBeamSource(
src=mp.GaussianSource(fcen, fwidth=0.2 * fcen),
center=mp.Vector3(src_x, src_y),
size=mp.Vector3(s),
beam_x0=beam_x0,
beam_kdir=beam_kdir,
beam_w0=beam_w0,
beam_E0=beam_E0,
)
]
sim = mp.Simulation(
resolution=resolution,
cell_size=cell_size,
boundary_layers=boundary_layers,
sources=sources,
)
cell_dft_fields = sim.add_dft_fields(
[mp.Ez],
fcen,
0,
1,
center=mp.Vector3(),
size=mp.Vector3(s - 2 * dpml, s - 2 * dpml),
)
sim.run(until_after_sources=50)
Ez_cell = sim.get_dft_array(cell_dft_fields, mp.Ez, 0)
[x, y, z, w] = sim.get_array_metadata(dft_cell=cell_dft_fields)
tol = 0.05
idx_x = np.nonzero(
(np.squeeze(x) > (src_x + beam_x0.x - tol))
& (np.squeeze(x) < (src_x + beam_x0.x + tol))
)
idx_y = np.nonzero(
(np.squeeze(y) > (src_y + beam_x0.y - tol))
& (np.squeeze(y) < (src_y + beam_x0.y + tol))
)
Ez_beam_x0 = Ez_cell[np.squeeze(idx_x)[0], np.squeeze(idx_y)[0]]
frac = np.abs(Ez_beam_x0) ** 2 / np.amax(np.abs(Ez_cell) ** 2)
print(
f"ratio of the Gaussian beam energy at the focus over the maximum beam energy for the entire cell: {frac}"
)
self.assertGreater(frac, 0.99)
def test_gaussian_beam(self):
self.gaussian_beam(-40)
if __name__ == "__main__":
unittest.main()
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