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import matplotlib.pyplot as plt
import numpy as np
import meep as mp
from meep import mpb
resolution = 128 # pixels/μm
Si = mp.Medium(index=3.45)
syz = 10
geometry_lattice = mp.Lattice(size=mp.Vector3(0, syz, syz))
k_points = [mp.Vector3(0.5)]
a = 1.0 # waveguide width
def parallel_waveguide(s, yodd):
geometry = [
mp.Block(
center=mp.Vector3(0, -0.5 * (s + a), 0),
size=mp.Vector3(mp.inf, a, a),
material=Si,
),
mp.Block(
center=mp.Vector3(0, 0.5 * (s + a), 0),
size=mp.Vector3(mp.inf, a, a),
material=Si,
),
]
ms = mpb.ModeSolver(
resolution=resolution,
k_points=k_points,
geometry_lattice=geometry_lattice,
geometry=geometry,
num_bands=1,
tolerance=1e-9,
)
if yodd:
ms.run_yodd_zodd()
else:
ms.run_yeven_zodd()
f = ms.get_freqs()[0]
vg = ms.compute_group_velocity_component(mp.Vector3(1, 0, 0))[0]
return f, vg
ss = np.arange(0.025, 1.075, 0.05)
f_odd = np.zeros(len(ss))
vg_odd = np.zeros(len(ss))
f_even = np.zeros(len(ss))
vg_even = np.zeros(len(ss))
for j in range(len(ss)):
f_odd[j], vg_odd[j] = parallel_waveguide(ss[j], True)
f_even[j], vg_even[j] = parallel_waveguide(ss[j], False)
ds = ss[1] - ss[0]
def compute_force(f, vg):
f_avg = 0.5 * (f[:-1] + f[1:])
df = f[1:] - f[:-1]
vg_avg = 0.5 * (vg[:-1] + vg[1:])
return -1 / f_avg * df / ds * 1 / vg_avg
force_odd = compute_force(f_odd, vg_odd)
force_even = compute_force(f_even, vg_even)
plt.figure(dpi=200)
plt.plot(ss[:-1], force_odd, "b-", label="anti-symmetric")
plt.plot(ss[:-1], force_even, "r-", label="symmetric")
plt.xlabel("waveguide separation s/a")
plt.ylabel("optical force (F/L)(ac/P)")
plt.legend(loc="upper right")
plt.xticks(np.arange(0, 1.2, 0.2))
plt.yticks(np.arange(-1.5, 1.0, 0.5))
plt.show()
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