plot2D missing block on multi-matrial system

[YiChunHung]

Hi all,

Currently, I am trying to simulate the grating structure with multiple materials (Au and GaAs).
After building the geometry, I visualized the geometry for checking.
However, the visualized result seems not to show the second block (gAu).

The following is my code. I hope someone could help me. Thanks.

import meep as mp
import numpy as np
import math
import matplotlib.pyplot as plt
from meep.materials import GaAs, Au, Au_JC_visible
from matplotlib import cm
tri_cmap = cm.get_cmap('gray_r',3)
nm = 0.001 #um
 
resolution = 200        # pixels/μm
 
dpml = 1.0             # PML thickness
dsub = 3000*nm          # substrate thickness
dpad = 3.0             # padding between grating and PML
gp = 10000*nm            # grating period
gh = 500*nm             # grating height
gdc = 0.5              # grating duty cycle
 
sx = dpml+dsub+gh+dpad+dpml
sy = gp
 
cell_size = mp.Vector3(sx,sy,0)
pml_layers = [mp.PML(thickness=dpml,direction=mp.X)]
 
 
wvl_min = 1           # min wavelength
wvl_max = 1.2           # max wavelength
fmin = 1/wvl_max        # min frequency
fmax = 1/wvl_min        # max frequency
fcen = 0.5*(fmin+fmax)  # center frequency
df = fmax-fmin          # frequency width
 
src_pt = mp.Vector3(-0.5*sx+dpml+0.5*dsub)
sources = [mp.Source(mp.GaussianSource(fcen, fwidth=df), component=mp.Ez, center=src_pt, size=mp.Vector3(y=sy))]
 
k_point = mp.Vector3(0,0,0)
symmetries=[mp.Mirror(mp.Y)]
 
geometries = []
gGaAs = mp.Block(material=GaAs, size=mp.Vector3(dpml+dsub,mp.inf,mp.inf), center=mp.Vector3(-0.5*sx+0.5*(dpml+dsub)))
gAu = mp.Block(material=Au, size=mp.Vector3(gh,gdc*gp,mp.inf), center=mp.Vector3(-0.5*sx+dpml+dsub+0.5*gh))
 
sim = mp.Simulation(resolution=resolution,
                    cell_size=cell_size,
                    boundary_layers=pml_layers,
                    k_point=k_point,
                    geometry=[gGaAs, gAu],
                    sources=sources,
                    symmetries=symmetries)
 
f2 = plt.figure(dpi=120)
sim.plot2D(ax=f2.gca(), labels=False, eps_parameters={'cmap':tri_cmap})
plt.savefig("geometry_GaAs.png")

[stevengj]

The epsilon output doesn't currently include frequency-dependent materials, and Au consists entirely of vacuum + frequency-dependent terms. Effectively, you are seeing the materials at ω=∞.

@oskooi, we discussed this in #415, but didn't we have a separate issue for supporting dispersive materials in get_epsilon and output_epsilon etcetera.

[YiChunHung]

@stevengj Thanks for your reply. So, if the material has the frequency-dependent term, the plot of geometry would be failed. What about the simulation result? Is it still be accurate?

[oskooi]

There is an FAQ on this exact topic but no issue.

(#628 is somewhat related but for the anisotropic permittivity/permeability tensor at ω=∞.)

[smartalecH]

Actually, I modified the routines awhile back to output epsilon at a frequency if the user provides an omega or if the user supplies a source (which you do). I've tested this pretty thoroughly so I'm surprised you are seeing this...

I can briefly look into it.

[smartalecH]

Aha! There's just too much dynamic range between your GaAs index and the Au index. I log-transformed the epsilon data and got the following:

It might be good to add a user passable function into the epsilon arguments so we can easily transform the data, similar to what we do with the fields. Obviously we need to update the docs with the "hidden" frequency evaluation feature.

Note: when evaluating epsilon at a particular frequency, it only returns the real part. The original purpose of the feature was to enable dispersive eigenmode coefficient calculations. MPB obviously only supports purely real materials (for now). Since it uses the same routines, you only get the real part (which is pretty small for these metals).

[YiChunHung]

@smartalecH Thanks for your kindly support! Since the problem has been detected and solved, I am gonna close the issue.