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import argparse
import matplotlib.pyplot as plt
import numpy as np
import numpy.matlib
import meep as mp
resolution = 60 # pixels/μm
dpml = 1.0 # PML thickness
dsub = 3.0 # substrate thickness
dpad = 3.0 # padding between grating and PML
wvl_min = 0.4 # min wavelength
wvl_max = 0.6 # max wavelength
fmin = 1 / wvl_max # min frequency
fmax = 1 / wvl_min # max frequency
fcen = 0.5 * (fmin + fmax) # center frequency
df = fmax - fmin # frequency width
nfreq = 21 # number of frequency bins
k_point = mp.Vector3(0, 0, 0)
glass = mp.Medium(index=1.5)
def grating(gp, gh, gdc, oddz):
sx = dpml + dsub + gh + dpad + dpml
sy = gp
cell_size = mp.Vector3(sx, sy, 0)
pml_layers = [mp.PML(thickness=dpml, direction=mp.X)]
src_pt = mp.Vector3(-0.5 * sx + dpml + 0.5 * dsub, 0, 0)
sources = [
mp.Source(
mp.GaussianSource(fcen, fwidth=df),
component=mp.Ez if oddz else mp.Hz,
center=src_pt,
size=mp.Vector3(0, sy, 0),
)
]
symmetries = [mp.Mirror(mp.Y, phase=+1 if oddz else -1)]
sim = mp.Simulation(
resolution=resolution,
cell_size=cell_size,
boundary_layers=pml_layers,
k_point=k_point,
default_material=glass,
sources=sources,
symmetries=symmetries,
)
mon_pt = mp.Vector3(0.5 * sx - dpml - 0.5 * dpad, 0, 0)
flux_mon = sim.add_flux(
fcen, df, nfreq, mp.FluxRegion(center=mon_pt, size=mp.Vector3(0, sy, 0))
)
sim.run(until_after_sources=100)
input_flux = mp.get_fluxes(flux_mon)
sim.reset_meep()
geometry = [
mp.Block(
material=glass,
size=mp.Vector3(dpml + dsub, mp.inf, mp.inf),
center=mp.Vector3(-0.5 * sx + 0.5 * (dpml + dsub), 0, 0),
),
mp.Block(
material=glass,
size=mp.Vector3(gh, gdc * gp, mp.inf),
center=mp.Vector3(-0.5 * sx + dpml + dsub + 0.5 * gh, 0, 0),
),
]
sim = mp.Simulation(
resolution=resolution,
cell_size=cell_size,
boundary_layers=pml_layers,
geometry=geometry,
k_point=k_point,
sources=sources,
symmetries=symmetries,
)
mode_mon = sim.add_flux(
fcen, df, nfreq, mp.FluxRegion(center=mon_pt, size=mp.Vector3(0, sy, 0))
)
sim.run(until_after_sources=300)
freqs = mp.get_eigenmode_freqs(mode_mon)
res = sim.get_eigenmode_coefficients(
mode_mon, [1], eig_parity=mp.ODD_Z + mp.EVEN_Y if oddz else mp.EVEN_Z + mp.ODD_Y
)
coeffs = res.alpha
mode_wvl = [1 / freqs[nf] for nf in range(nfreq)]
mode_tran = [abs(coeffs[0, nf, 0]) ** 2 / input_flux[nf] for nf in range(nfreq)]
mode_phase = [np.angle(coeffs[0, nf, 0]) for nf in range(nfreq)]
return mode_wvl, mode_tran, mode_phase
if __name__ == "__main__":
parser = argparse.ArgumentParser()
parser.add_argument(
"-gp", type=float, default=0.35, help="grating periodicity (default: 0.35 μm)"
)
parser.add_argument(
"-gh", type=float, default=0.6, help="grating height (default: 0.6 μm)"
)
parser.add_argument(
"-oddz", action="store_true", default=False, help="oddz? (default: False)"
)
args = parser.parse_args()
gdc = np.arange(0.1, 1.0, 0.1)
mode_tran = np.empty((gdc.size, nfreq))
mode_phase = np.empty((gdc.size, nfreq))
for n in range(gdc.size):
mode_wvl, mode_tran[n, :], mode_phase[n, :] = grating(
args.gp, args.gh, gdc[n], args.oddz
)
plt.figure(dpi=150)
plt.subplot(1, 2, 1)
plt.pcolormesh(
mode_wvl,
gdc,
mode_tran,
cmap="hot_r",
shading="gouraud",
vmin=0,
vmax=mode_tran.max(),
)
plt.axis([wvl_min, wvl_max, gdc[0], gdc[-1]])
plt.xlabel("wavelength (μm)")
plt.xticks(list(np.arange(wvl_min, wvl_max + 0.1, 0.1)))
plt.ylabel("grating duty cycle")
plt.yticks(list(np.arange(gdc[0], gdc[-1] + 0.1, 0.1)))
plt.title("transmittance")
cbar = plt.colorbar()
cbar.set_ticks(list(np.arange(0, 1.2, 0.2)))
cbar.set_ticklabels([f"{t:.1f}" for t in np.arange(0, 1.2, 0.2)])
plt.subplot(1, 2, 2)
plt.pcolormesh(
mode_wvl,
gdc,
mode_phase,
cmap="RdBu",
shading="gouraud",
vmin=mode_phase.min(),
vmax=mode_phase.max(),
)
plt.axis([wvl_min, wvl_max, gdc[0], gdc[-1]])
plt.xlabel("wavelength (μm)")
plt.xticks(list(np.arange(wvl_min, wvl_max + 0.1, 0.1)))
plt.ylabel("grating duty cycle")
plt.yticks(list(np.arange(gdc[0], gdc[-1] + 0.1, 0.1)))
plt.title("phase (radians)")
cbar = plt.colorbar()
cbar.set_ticks(list(range(-3, 4)))
cbar.set_ticklabels([f"{t:.1f}" for t in range(-3, 4)])
plt.tight_layout()
plt.show()
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