Issues mapping materials from library (but works in plot2D)

[deme0097]

It seems that when use component=mp.Dielectric I can get accurate vaules for my geometry when using materials with user assigned index values. But when I try using a material from the library (e.g. material=Au) I only get air in the material's place. The simulation still seems to run correctly but I would like to map this data as a check.

To check this I also used the plot2D function. There I see my material but not when I try to extract the data myself. What is going on? Also is there a way to extract the complex permitivity or does component=mp.Dielectric only give the real values?

I'm fairly new to MEEP so thanks all for any insights!

import meep as mp
from meep.materials import Au
import numpy as np
import matplotlib.pyplot as plt
import os

a_meep = 1 #um
wl = 0.5

## Set default values
res_min = 8*(a_meep/wl)
resolution = 100 #sample points per characteristic length a, [samples/um]
if resolution <= res_min:
    print(f"Error: Resolution should be greater than {int(res_min)}. Please adjust the resolution.")
    exit()

dpml = .5  # Thickness (um) of perfectly matched layer (PML) 
dair = 1  # Thickness of air padding
hrod = 0.4  # Height of rod
wrod = 0.6  # Width of rod
dfilm = 0.2  # Thickness of resonator layer
dsub = .5  # Thickness of substrate

sx = 1  # Size in x-direction (um)
sy = 2*dpml+dair+hrod+dfilm+dsub   # Size in y-direction (um)
cell_size = mp.Vector3(sx,sy,0) #2D computational cell region (um)

fcen_meep = a_meep/wl  #Center freq, consistent with MEEP units 1/wl (since a=1um and c=1)
df = 0.01  # Frequency width
print("MEEP Frequency:", fcen_meep)

run_time = 10 * fcen_meep  

pml_layers = [mp.PML(direction=mp.Y, thickness=dpml, side=mp.High),
    mp.PML(direction=mp.Y, thickness=dpml, side=mp.Low)]

## Specify the solid geometric objects. 
#=======================================================================
substrate = mp.Block(material=mp.Medium(index=1.5),          
                     center=mp.Vector3(0, -0.5*sy + 0.5*dpml + 0.5*dsub),
                     size=mp.Vector3(mp.inf, dsub + dpml, mp.inf))   #want the material to extend into the PML

film = mp.Block(material=Au, #mp.Medium(index=2.6),  ..works when defined but not when I use a material from library. Then all 1???
                     center=mp.Vector3(0, -0.5*sy + dsub + dpml + 0.5*dfilm),
                     size=mp.Vector3(mp.inf, dfilm, mp.inf))

Monitor_loc = mp.Vector3(0, 0.5*sy - dpml - 1 )

structure = [substrate, film]
#=======================================================================

def compute_flux(fcen, df, structure, Monitor_loc):
    """
    Computes the frequency response (flux) for a given configuration.
    Returns:
    - freqs (numpy.ndarray): Array of frequency values.
    - flux (numpy.ndarray): Array of flux values corresponding to the specified configuration.
    - magnitude_electric_field
    """
    save_dir = os.path.join(os.getcwd(), 'Results Simple')
    # Create a pulsed Gaussian source at the top of the simulation in air
    sources = [mp.Source(mp.ContinuousSource(fcen,df,is_integrated=True),
                         component=mp.Ex,
                         center=mp.Vector3(0, 0.5*sy-dpml-0.25,0),
                         size=mp.Vector3(sx,0,0))]

    # #Create and run the simulation
    sim = mp.Simulation(cell_size=cell_size,
                        resolution=resolution, #how does it read this???
                        k_point=mp.Vector3(0,0,0),  # Bloch-periodic boundary conditions 
                        boundary_layers=pml_layers,
                        geometry=structure,
                        sources=sources)

    sim.plot2D(label_geometry=True,labels=True,
                eps_parameters={'colorbar': True},
                boundary_parameters={'alpha':0.5,'hatch':'/', 'linewidth':1.5, 'facecolor':'r', 'edgecolor':'k'})
    
    plot2D_save_path = os.path.join(save_dir, "plot2D_figure2.png")
    plt.savefig(plot2D_save_path, dpi=100, bbox_inches="tight")

    Ex_data = sim.get_array(center=mp.Vector3(), size=cell_size, component=mp.Ex)
    Ey_data = sim.get_array(center=mp.Vector3(), size=cell_size, component=mp.Ey)
    Ez_data = sim.get_array(center=mp.Vector3(), size=cell_size, component=mp.Ez)
    magnitude_electric_field = np.sqrt(Ex_data**2 + Ey_data**2 + Ez_data**2)  

    # Get the refractive index
    epsilon_data = sim.get_array(center=mp.Vector3(), size=cell_size, component=mp.Dielectric)
    n_real_data = np.sqrt(0.5*(np.abs(epsilon_data) + np.real(epsilon_data)))  

    x = np.linspace(-0.5 * sx, 0.5 * sx, epsilon_data.shape[0])
    y = np.linspace(-0.5 * sy, 0.5 * sy, epsilon_data.shape[1])

    # Plot the real part of the refractive index
    plt.figure()
    plt.imshow(n_real_data.transpose(), interpolation="none", cmap="turbo", extent=[x.min(), x.max(), y.min(), y.max()], origin='lower')
    plt.axis("on")
    plt.title("Real Part of n")
    cbar = plt.colorbar()
    # Save the figure to the specified directory
    save_path = os.path.join(save_dir, "cell_geometry_cross_section.png")
    plt.savefig(save_path, dpi=100, bbox_inches="tight")

    return magnitude_electric_field, x, y

save_directory = os.path.join(os.getcwd(), 'Results Simple')
os.makedirs(save_directory, exist_ok=True)

E_T,x,y = compute_flux(fcen_meep,df,structure, Monitor_loc)

plt.figure()
image2 = plt.imshow(E_T.transpose(), interpolation="None", cmap="turbo", extent=[x.min(), x.max(), y.min(), y.max()], origin='lower')
plt.axis("on")
plt.colorbar(image2, orientation='vertical', label='Electric Field Magnitude')
plt.title("Electric Field Distribution X- Textured Structure")

save_path_T = os.path.join(save_directory, "Electric_Field_Distribution.png")
plt.savefig(save_path_T, dpi=100, bbox_inches="tight")'

[smartalecH]

Plot2D is "smart" in that it looks at your sources, pulls the center frequency, and uses that to evaluate your (complex) Drude-Lorentz model.

When you dump your structure naively, it's not smart. And will just return the (real) DC component of your material model. Some routines let you pass in an optional frequency parameter. It'd be good to go through the docs to check exactly which ones (get_array() should).

[deme0097]

Yes, passing the frequency to get_array resolved the issue. Thank you!