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import matplotlib.pyplot as plt
import numpy as np
import meep as mp
resolution = 40 # pixels/μm
Si = mp.Medium(index=3.45)
dpml = 1.0
pml_layers = [mp.PML(dpml)]
sx = 5
sy = 3
cell = mp.Vector3(sx + 2 * dpml, sy + 2 * dpml, 0)
a = 1.0 # waveguide width/height
k_point = mp.Vector3(z=0.5)
def parallel_waveguide(s, xodd):
geometry = [
mp.Block(
center=mp.Vector3(-0.5 * (s + a)),
size=mp.Vector3(a, a, mp.inf),
material=Si,
),
mp.Block(
center=mp.Vector3(0.5 * (s + a)), size=mp.Vector3(a, a, mp.inf), material=Si
),
]
symmetries = [mp.Mirror(mp.X, phase=-1 if xodd else 1), mp.Mirror(mp.Y, phase=-1)]
sim = mp.Simulation(
resolution=resolution,
cell_size=cell,
geometry=geometry,
boundary_layers=pml_layers,
symmetries=symmetries,
k_point=k_point,
)
sim.init_sim()
EigenmodeData = sim.get_eigenmode(
0.22,
mp.Z,
mp.Volume(center=mp.Vector3(), size=mp.Vector3(sx, sy)),
2 if xodd else 1,
k_point,
match_frequency=False,
parity=mp.ODD_Y,
)
fcen = EigenmodeData.freq
print(f'freq:, {"xodd" if xodd else "xeven"}, {s}, {fcen}')
sim.reset_meep()
eig_sources = [
mp.EigenModeSource(
src=mp.GaussianSource(fcen, fwidth=0.1 * fcen),
size=mp.Vector3(sx, sy),
center=mp.Vector3(),
eig_band=2 if xodd else 1,
eig_kpoint=k_point,
eig_match_freq=False,
eig_parity=mp.ODD_Y,
)
]
sim.change_sources(eig_sources)
flux_reg = mp.FluxRegion(
direction=mp.Z, center=mp.Vector3(), size=mp.Vector3(sx, sy)
)
wvg_flux = sim.add_flux(fcen, 0, 1, flux_reg)
force_reg1 = mp.ForceRegion(
mp.Vector3(0.49 * s), direction=mp.X, weight=1, size=mp.Vector3(y=sy)
)
force_reg2 = mp.ForceRegion(
mp.Vector3(0.5 * s + 1.01 * a), direction=mp.X, weight=-1, size=mp.Vector3(y=sy)
)
wvg_force = sim.add_force(fcen, 0, 1, force_reg1, force_reg2)
sim.run(until_after_sources=1500)
flux = mp.get_fluxes(wvg_flux)[0]
force = mp.get_forces(wvg_force)[0]
print(
f'data:, {"xodd" if xodd else "xeven"}, {s}, {flux}, {force}, {-force / flux}'
)
sim.reset_meep()
return flux, force
s = np.arange(0.05, 1.05, 0.05)
fluxes_odd = np.zeros(s.size)
forces_odd = np.zeros(s.size)
fluxes_even = np.zeros(s.size)
forces_even = np.zeros(s.size)
for k in range(len(s)):
fluxes_odd[k], forces_odd[k] = parallel_waveguide(s[k], True)
fluxes_even[k], forces_even[k] = parallel_waveguide(s[k], False)
plt.figure(dpi=150)
plt.plot(s, -forces_odd / fluxes_odd, "rs", label="anti-symmetric")
plt.plot(s, -forces_even / fluxes_even, "bo", label="symmetric")
plt.grid(True)
plt.xlabel("waveguide separation s/a")
plt.ylabel("optical force (F/L)(ac/P)")
plt.legend(loc="upper right")
plt.show()
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