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# Calculating 2d ring-resonator modes using cylindrical coordinates,
# from the Meep tutorial.
import argparse
import meep as mp
def main(args):
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 = 32 # thickness of PML
sr = r + w + pad + dpml # radial size (cell is from 0 to sr)
dimensions = mp.CYLINDRICAL
cell = mp.Vector3(sr, 0, 0)
# in cylindrical coordinates, the phi (angular) dependence of the fields
# is given by exp(i m phi), where m is given by:
m = args.m
geometry = [
mp.Block(
center=mp.Vector3(r + (w / 2)),
size=mp.Vector3(w, mp.inf, mp.inf),
material=mp.Medium(index=n),
)
]
pml_layers = [mp.PML(dpml)]
resolution = 20
# 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 = args.fcen # pulse center frequency
df = args.df # pulse frequency width
sources = [
mp.Source(
src=mp.GaussianSource(fcen, fwidth=df),
component=mp.Ez,
center=mp.Vector3(r + 0.1),
)
]
# note that the r -> -r mirror symmetry is exploited automatically
sim = mp.Simulation(
cell_size=cell,
geometry=geometry,
boundary_layers=pml_layers,
resolution=resolution,
sources=sources,
dimensions=dimensions,
m=m,
)
sim.run(
mp.after_sources(mp.Harminv(mp.Ez, mp.Vector3(r + 0.1), fcen, df)),
until_after_sources=200,
)
# 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.) We'll append the fields
# to a file to get an r-by-t picture. We'll also output from -sr to -sr
# instead of from 0 to sr.
sim.run(
mp.in_volume(
mp.Volume(center=mp.Vector3(), size=mp.Vector3(2 * sr)),
mp.at_beginning(mp.output_epsilon),
mp.to_appended("ez", mp.at_every(1 / fcen / 20, mp.output_efield_z)),
),
until=1 / fcen,
)
if __name__ == "__main__":
parser = argparse.ArgumentParser()
parser.add_argument(
"-fcen", type=float, default=0.15, help="pulse center frequency"
)
parser.add_argument("-df", type=float, default=0.1, help="pulse frequency width")
parser.add_argument(
"-m",
type=int,
default=3,
help="phi (angular) dependence of the fields given by exp(i m phi)",
)
args = parser.parse_args()
main(args)
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