ring-cyl.py

# Calculating 2d ring-resonator modes using cylindrical coordinates,
# from the Meep tutorial.
from __future__ import division

import meep as mp
import argparse

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)