S11 and S12 of a straight waveguide

waveguide_mode_coeffs.py

import meep as mp
import numpy as np

cell_size = mp.Vector3(14,14)

pml_layers = [mp.PML(thickness=2)]

w = 1.0
geometry = [mp.Block(center=mp.Vector3(),
                     size=mp.Vector3(mp.inf,w,mp.inf),
                     material=mp.Medium(epsilon=12))]

fsrc = 0.15
sources = [mp.EigenModeSource(src=mp.GaussianSource(fsrc,fwidth=0.2*fsrc),
                              center=mp.Vector3(),
                              size=mp.Vector3(y=3*w),
                              direction=mp.NO_DIRECTION,
                              eig_kpoint=mp.Vector3(1,0,0),
                              eig_parity=mp.EVEN_Y+mp.ODD_Z)]

for res in [25, 50, 100, 200, 400]:

    sim = mp.Simulation(cell_size=cell_size,
			resolution=res,
			boundary_layers=pml_layers,
			sources=sources,
			geometry=geometry,
			symmetries=[mp.Mirror(mp.Y)])

    tran = sim.add_mode_monitor(fsrc, 0, 1,
				mp.ModeRegion(center=mp.Vector3(x=5),
                                size=mp.Vector3(y=14)),
				yee_grid=True)

    sim.run(until_after_sources=50)
    
    res_fwd = sim.get_eigenmode_coefficients(tran,
                                             [1],
                                             eig_parity=mp.EVEN_Y+mp.ODD_Z,
                                             direction=mp.NO_DIRECTION,
                                             kpoint_func=lambda f,n: mp.Vector3(+1,0,0))

    res_bwd = sim.get_eigenmode_coefficients(tran,
                                             [1],
                                             eig_parity=mp.EVEN_Y+mp.ODD_Z,
                                             direction=mp.NO_DIRECTION,
                                             kpoint_func=lambda f,n: mp.Vector3(-1,0,0))

    ## res_fwd: alpha[0,0,0] --> S21, alpha[0,0,1] --> S11
    print("flux-fwd:, {}, {:.10f}, {:.10f}".format(res,abs(res_fwd.alpha[0,0,0])**2,abs(res_fwd.alpha[0,0,1])**2))

    ## res_bwd: alpha[0,0,0] --> S11, alpha[0,0,1] --> S21
    print("flux-bwd:, {}, {:.10f}, {:.10f}".format(res,abs(res_bwd.alpha[0,0,0])**2,abs(res_bwd.alpha[0,0,1])**2))