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# transmission around a 90-degree waveguide bend in 2d
import matplotlib.pyplot as plt
import numpy as np
import meep as mp
resolution = 10 # pixels/um
sx = 16 # size of cell in X direction
sy = 32 # size of cell in Y direction
cell = mp.Vector3(sx, sy, 0)
dpml = 1.0
pml_layers = [mp.PML(dpml)]
pad = 4 # padding distance between waveguide and cell edge
w = 1 # width of waveguide
wvg_xcen = 0.5 * (sx - w - 2 * pad) # x center of vert. wvg
wvg_ycen = -0.5 * (sy - w - 2 * pad) # y center of horiz. wvg
geometry = [
mp.Block(
size=mp.Vector3(mp.inf, w, mp.inf),
center=mp.Vector3(0, wvg_ycen, 0),
material=mp.Medium(epsilon=12),
)
]
fcen = 0.15 # pulse center frequency
df = 0.1 # pulse width (in frequency)
sources = [
mp.Source(
mp.GaussianSource(fcen, fwidth=df),
component=mp.Ez,
center=mp.Vector3(-0.5 * sx + dpml, wvg_ycen, 0),
size=mp.Vector3(0, w, 0),
)
]
sim = mp.Simulation(
cell_size=cell,
boundary_layers=pml_layers,
geometry=geometry,
sources=sources,
resolution=resolution,
)
nfreq = 100 # number of frequencies at which to compute flux
# reflected flux
refl_fr = mp.FluxRegion(
center=mp.Vector3(-0.5 * sx + dpml + 0.5, wvg_ycen, 0), size=mp.Vector3(0, 2 * w, 0)
)
refl = sim.add_flux(fcen, df, nfreq, refl_fr)
# transmitted flux
tran_fr = mp.FluxRegion(
center=mp.Vector3(0.5 * sx - dpml, wvg_ycen, 0), size=mp.Vector3(0, 2 * w, 0)
)
tran = sim.add_flux(fcen, df, nfreq, tran_fr)
pt = mp.Vector3(0.5 * sx - dpml - 0.5, wvg_ycen)
sim.run(until_after_sources=mp.stop_when_fields_decayed(50, mp.Ez, pt, 1e-3))
# for normalization run, save flux fields data for reflection plane
straight_refl_data = sim.get_flux_data(refl)
# save incident power for transmission plane
straight_tran_flux = mp.get_fluxes(tran)
sim.reset_meep()
geometry = [
mp.Block(
mp.Vector3(sx - pad, w, mp.inf),
center=mp.Vector3(-0.5 * pad, wvg_ycen),
material=mp.Medium(epsilon=12),
),
mp.Block(
mp.Vector3(w, sy - pad, mp.inf),
center=mp.Vector3(wvg_xcen, 0.5 * pad),
material=mp.Medium(epsilon=12),
),
]
sim = mp.Simulation(
cell_size=cell,
boundary_layers=pml_layers,
geometry=geometry,
sources=sources,
resolution=resolution,
)
# reflected flux
refl = sim.add_flux(fcen, df, nfreq, refl_fr)
tran_fr = mp.FluxRegion(
center=mp.Vector3(wvg_xcen, 0.5 * sy - dpml - 0.5, 0), size=mp.Vector3(2 * w, 0, 0)
)
tran = sim.add_flux(fcen, df, nfreq, tran_fr)
# for normal run, load negated fields to subtract incident from refl. fields
sim.load_minus_flux_data(refl, straight_refl_data)
pt = mp.Vector3(wvg_xcen, 0.5 * sy - dpml - 0.5)
sim.run(until_after_sources=mp.stop_when_fields_decayed(50, mp.Ez, pt, 1e-3))
bend_refl_flux = mp.get_fluxes(refl)
bend_tran_flux = mp.get_fluxes(tran)
flux_freqs = mp.get_flux_freqs(refl)
wl = []
Rs = []
Ts = []
for i in range(nfreq):
wl = np.append(wl, 1 / flux_freqs[i])
Rs = np.append(Rs, -bend_refl_flux[i] / straight_tran_flux[i])
Ts = np.append(Ts, bend_tran_flux[i] / straight_tran_flux[i])
if mp.am_master():
plt.figure()
plt.plot(wl, Rs, "bo-", label="reflectance")
plt.plot(wl, Ts, "ro-", label="transmittance")
plt.plot(wl, 1 - Rs - Ts, "go-", label="loss")
plt.axis([5.0, 10.0, 0, 1])
plt.xlabel("wavelength (μm)")
plt.legend(loc="upper right")
plt.show()
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