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# Calculating 2d ring-resonator modes, from the Meep tutorial.
import meep as mp
def main():
n = 3.4 # index of waveguide
w = 1 # width of waveguide
r = 1 # inner radius of ring
pad = 4 # padding between waveguide and edge of PML
dpml = 2 # thickness of PML
sxy = 2 * (r + w + pad + dpml) # cell size
# Create a ring waveguide by two overlapping cylinders - later objects
# take precedence over earlier objects, so we put the outer cylinder first.
# and the inner (air) cylinder second.
c1 = mp.Cylinder(radius=r + w, material=mp.Medium(index=n))
c2 = mp.Cylinder(radius=r)
# If we don't want to excite a specific mode symmetry, we can just
# put a single point source at some arbitrary place, pointing in some
# arbitrary direction. We will only look for Ez-polarized modes.
fcen = 0.15 # pulse center frequency
df = 0.1 # pulse width (in frequency)
src = mp.Source(mp.GaussianSource(fcen, fwidth=df), mp.Ez, mp.Vector3(r + 0.1))
sim = mp.Simulation(
cell_size=mp.Vector3(sxy, sxy),
geometry=[c1, c2],
sources=[src],
resolution=10,
symmetries=[mp.Mirror(mp.Y)],
boundary_layers=[mp.PML(dpml)],
)
sim.run(
mp.at_beginning(mp.output_epsilon),
mp.after_sources(mp.Harminv(mp.Ez, mp.Vector3(r + 0.1), fcen, df)),
until_after_sources=300,
)
# Output fields for one period at the end. (If we output
# at a single time, we might accidentally catch the Ez field when it is
# almost zero and get a distorted view.)
sim.run(mp.at_every(1 / fcen / 20, mp.output_efield_z), until=1 / fcen)
if __name__ == "__main__":
main()
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