Germanium Fano metasurface ¶

# standard python imports
import numpy as np
import matplotlib.pyplot as plt

# tidy3D import
import tidy3d as td
from tidy3d import web

Nfreq = 1000
wavelengths = np.linspace(8, 12, Nfreq)
freqs = td.constants.C_0 / wavelengths
freq0 = freqs[len(freqs) // 2]
freqw = freqs[0] - freqs[-1]

# Define material properties
n_BaF2 = 1.45
n_Ge = 4
BaF2 = td.Medium(permittivity=n_BaF2**2)
Ge = td.Medium(permittivity=n_Ge**2)

# space between resonators and source
spc = 8

# geometric parameters
Px = Py = P = 4.2
h = 2.53
L1 = 3.036
L2 = 2.024
w1 = w2 = w = 1.265

# resolution (should be commensurate with periodicity)
dl = P / 32

# total size in z and [x,y,z]
Lz = spc + h + h + spc
sim_size = [Px, Py, Lz]

# BaF2 substrate
substrate = td.Structure(
    geometry=td.Box(
        center=[0, 0, -Lz / 2],
        size=[td.inf, td.inf, 2 * (spc + h)],
    ),
    medium=BaF2,
    name="substrate",
)

# Define structure

cell1 = td.Structure(
    geometry=td.Box(
        center=[(L1 / 2) - L2, -w1 / 2, h / 2],
        size=[L1, w1, h],
    ),
    medium=Ge,
    name="cell1",
)

cell2 = td.Structure(
    geometry=td.Box(
        center=[-L2 / 2, w2 / 2, h / 2],
        size=[L2, w2, h],
    ),
    medium=Ge,
    name="cell2",
)

# time dependence of source
gaussian = td.GaussianPulse(freq0=freq0, fwidth=freqw)

# plane wave source
source = td.PlaneWave(
    source_time=gaussian,
    size=(td.inf, td.inf, 0),
    center=(0, 0, Lz / 2 - spc + 2 * dl),
    direction="-",
    pol_angle=0,
)

# Simulation run time.  Note you need to run a long time to calculate high Q resonances.
run_time = 8e-11

# monitor fields on other side of structure (substrate side) at range of frequencies
monitor = td.FluxMonitor(
    center=[0.0, 0.0, -Lz / 2 + spc - 2 * dl],
    size=[td.inf, td.inf, 0],
    freqs=freqs,
    name="flux",
)

grid_spec = td.GridSpec(
    grid_x=td.UniformGrid(dl=dl),
    grid_y=td.UniformGrid(dl=dl),
    grid_z=td.AutoGrid(min_steps_per_wvl=32),
)

# normalizing run (no Ge) to get baseline transmission vs freq
# can be run for shorter time as there are no resonances
sim_empty = td.Simulation(
    size=sim_size,
    grid_spec=grid_spec,
    structures=[substrate],
    sources=[source],
    monitors=[monitor],
    run_time=run_time / 10,
    boundary_spec=td.BoundarySpec(
        x=td.Boundary.periodic(), y=td.Boundary.periodic(), z=td.Boundary.pml()
    ),
)

# run with Ge nanorod
sim_actual = td.Simulation(
    size=sim_size,
    grid_spec=td.GridSpec.uniform(dl=dl),
    structures=[substrate, cell1, cell2],
    sources=[source],
    monitors=[monitor],
    run_time=run_time,
    boundary_spec=td.BoundarySpec(
        x=td.Boundary.periodic(), y=td.Boundary.periodic(), z=td.Boundary.pml()
    ),
)