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import matplotlib
import numpy as np
import meep as mp
matplotlib.use("agg")
import matplotlib.pyplot as plt
resolution = 20 # pixels/μm
fcen = 0.25 # pulse center frequency
df = 0.2 # pulse width (in frequency)
eps = 13 # dielectric constant of waveguide
w = 1.2 # width of waveguide
r = 0.36 # radius of holes
d = 1.4 # defect spacing (ordinary spacing = 1)
N = 3 # number of holes on either side of defect
dpad = 32 # padding between last hole and PML edge
dpml = 0.5 / (fcen - 0.5 * df) # PML thickness (> half the largest wavelength)
sx = 2 * (dpad + dpml + N) + d - 1 # size of cell in x direction
d1 = 0.2 # y-distance from waveguide edge to near2far surface
d2 = 2.0 # y-distance from near2far surface to far-field line
sy = w + 2 * (d1 + d2 + dpml) # size of cell in y direction (perpendicular to wvg.)
cell = mp.Vector3(sx, sy, 0)
geometry = [
mp.Block(
center=mp.Vector3(),
size=mp.Vector3(mp.inf, w, mp.inf),
material=mp.Medium(epsilon=eps),
)
]
for i in range(N):
geometry.append(mp.Cylinder(r, center=mp.Vector3(d / 2 + i)))
geometry.append(mp.Cylinder(r, center=mp.Vector3(d / -2 - i)))
pml_layers = [mp.PML(dpml)]
sources = [
mp.Source(
src=mp.GaussianSource(fcen, fwidth=df), component=mp.Hz, center=mp.Vector3()
)
]
symmetries = [mp.Mirror(mp.X, phase=-1), mp.Mirror(mp.Y, phase=-1)]
sim = mp.Simulation(
cell_size=cell,
geometry=geometry,
sources=sources,
symmetries=symmetries,
boundary_layers=pml_layers,
resolution=resolution,
)
nearfield = sim.add_near2far(
fcen,
0,
1,
mp.Near2FarRegion(mp.Vector3(0, 0.5 * w + d1), size=mp.Vector3(sx - 2 * dpml)),
mp.Near2FarRegion(
mp.Vector3(-0.5 * sx + dpml, 0.5 * w + 0.5 * d1),
size=mp.Vector3(0, d1),
weight=-1.0,
),
mp.Near2FarRegion(
mp.Vector3(0.5 * sx - dpml, 0.5 * w + 0.5 * d1), size=mp.Vector3(0, d1)
),
)
mon = sim.add_dft_fields(
[mp.Hz],
fcen,
0,
1,
center=mp.Vector3(0, 0.5 * w + d1 + d2),
size=mp.Vector3(sx - 2 * (dpad + dpml), 0),
)
sim.run(until_after_sources=mp.stop_when_dft_decayed())
sim.plot2D()
if mp.am_master():
plt.savefig(
f"cavity_farfield_plot2D_dpad{dpad}_{d1}_{d2}.png", bbox_inches="tight", dpi=150
)
Hz_mon = sim.get_dft_array(mon, mp.Hz, 0)
(x, y, z, w) = sim.get_array_metadata(dft_cell=mon)
ff = []
for xc in x:
ff_pt = sim.get_farfield(nearfield, mp.Vector3(xc, y[0]))
ff.append(ff_pt[5])
ff = np.array(ff)
if mp.am_master():
plt.figure()
plt.subplot(1, 3, 1)
plt.plot(np.real(Hz_mon), "bo-", label="DFT")
plt.plot(np.real(ff), "ro-", label="N2F")
plt.legend()
plt.xlabel("$x$ (μm)")
plt.ylabel("real(Hz)")
plt.subplot(1, 3, 2)
plt.plot(np.imag(Hz_mon), "bo-", label="DFT")
plt.plot(np.imag(ff), "ro-", label="N2F")
plt.legend()
plt.xlabel("$x$ (μm)")
plt.ylabel("imag(Hz)")
plt.subplot(1, 3, 3)
plt.plot(np.abs(Hz_mon), "bo-", label="DFT")
plt.plot(np.abs(ff), "ro-", label="N2F")
plt.legend()
plt.xlabel("$x$ (μm)")
plt.ylabel("|Hz|")
plt.suptitle(
f"comparison of near2far and actual DFT fields\n dpad={dpad}, d1={d1}, d2={d2}"
)
plt.subplots_adjust(wspace=0.6)
plt.savefig(
f"test_Hz_dft_vs_n2f_res{resolution}_dpad{dpad}_d1{d1}_d2{d2}.png",
bbox_inches="tight",
dpi=150,
)
|
