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tutorial and unit test for mode sources using DiffractedPlanewave object #2072

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c4e6e21
tutorial and unit test for mode source using DiffractedPlanewave object
oskooi May 13, 2022
f700429
slightly increase tolerance for single-precision build
oskooi May 14, 2022
a35f867
fixes
oskooi Jun 3, 2022
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24 changes: 19 additions & 5 deletions doc/docs/Python_Tutorials/Eigenmode_Source.md
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Original file line number Diff line number Diff line change
Expand Up @@ -234,6 +234,8 @@ The simulation script is in [examples/oblique-planewave.py](https://github.com/N
```py
import meep as mp
import numpy as np
import matplotlib
matplotlib.use('agg')
import matplotlib.pyplot as plt

resolution = 50 # pixels/μm
Expand All @@ -243,9 +245,9 @@ cell_size = mp.Vector3(14,10,0)
pml_layers = [mp.PML(thickness=2,direction=mp.X)]

# rotation angle (in degrees) of planewave, counter clockwise (CCW) around z-axis
rot_angle = np.radians(0)
rot_angle = np.radians(23.2)

fsrc = 1.0 # frequency of planewave (wavelength = 1/fsrc)
fsrc = 1.0 # frequency (wavelength = 1/fsrc)

n = 1.5 # refractive index of homogeneous material
default_material = mp.Medium(index=n)
Expand All @@ -258,8 +260,7 @@ sources = [mp.EigenModeSource(src=mp.ContinuousSource(fsrc),
direction=mp.AUTOMATIC if rot_angle == 0 else mp.NO_DIRECTION,
eig_kpoint=k_point,
eig_band=1,
eig_parity=mp.EVEN_Y+mp.ODD_Z if rot_angle == 0 else mp.ODD_Z,
eig_match_freq=True)]
eig_parity=mp.EVEN_Y+mp.ODD_Z if rot_angle == 0 else mp.ODD_Z)]

sim = mp.Simulation(cell_size=cell_size,
resolution=resolution,
Expand All @@ -269,11 +270,12 @@ sim = mp.Simulation(cell_size=cell_size,
default_material=default_material,
symmetries=[mp.Mirror(mp.Y)] if rot_angle == 0 else [])

sim.run(until=100)
sim.run(until=20)

nonpml_vol = mp.Volume(center=mp.Vector3(), size=mp.Vector3(10,10,0))

sim.plot2D(fields=mp.Ez,
plot_boundaries_flag=False,
output_plane=nonpml_vol)

if mp.am_master():
Expand All @@ -288,3 +290,15 @@ Shown below are the steady-state field profiles generated by the planewave for t
<center>
![](../images/eigenmode_planewave.png)
</center>

An alternative method to launching a planewave in homogeneous media which provides more control over specifying its polarization, particularly in 3D, is to use a `DiffractedPlanewave` object for the `eig_band` property of the `EigenModeSource` instead of a band number and parity as in the previous example which used 1 and `mp.ODD_Z`, respectively. A planewave with wavevector $\vec{k}$ can be defined using the *zeroth* diffraction order combined with the `k_point` of the `Simulation` object set to $\vec{k}$. As a demonstration, the previous example which involved an $E_z$-polarized source (equivalent to the $\mathcal{S}$ polarization given the plane of incidence of $xy$), can also be defined using:

```py
sources = [mp.EigenModeSource(src=mp.ContinuousSource(fsrc),
center=mp.Vector3(),
size=mp.Vector3(y=10),
eig_band=mp.DiffractedPlanewave((0,0,0),
mp.Vector3(0,1,0),
1,
0))]
```
22 changes: 17 additions & 5 deletions python/examples/oblique-planewave.py
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Original file line number Diff line number Diff line change
@@ -1,17 +1,20 @@
import meep as mp
import numpy as np
import matplotlib
matplotlib.use('agg')
import matplotlib.pyplot as plt


resolution = 50 # pixels/μm

cell_size = mp.Vector3(14,10,0)

pml_layers = [mp.PML(thickness=2,direction=mp.X)]

# rotation angle (in degrees) of planewave, counter clockwise (CCW) around z-axis
rot_angle = np.radians(0)
rot_angle = np.radians(23.2)

fsrc = 1.0 # frequency of planewave (wavelength = 1/fsrc)
fsrc = 1.0 # frequency (wavelength = 1/fsrc)

n = 1.5 # refractive index of homogeneous material
default_material = mp.Medium(index=n)
Expand All @@ -24,8 +27,16 @@
direction=mp.AUTOMATIC if rot_angle == 0 else mp.NO_DIRECTION,
eig_kpoint=k_point,
eig_band=1,
eig_parity=mp.EVEN_Y+mp.ODD_Z if rot_angle == 0 else mp.ODD_Z,
eig_match_freq=True)]
eig_parity=mp.EVEN_Y+mp.ODD_Z if rot_angle == 0 else mp.ODD_Z)]

## equivalent definition
# sources = [mp.EigenModeSource(src=mp.ContinuousSource(fsrc),
# center=mp.Vector3(),
# size=mp.Vector3(y=10),
# eig_band=mp.DiffractedPlanewave((0,0,0),
# mp.Vector3(0,1,0),
# 1,
# 0))]

sim = mp.Simulation(cell_size=cell_size,
resolution=resolution,
Expand All @@ -35,11 +46,12 @@
default_material=default_material,
symmetries=[mp.Mirror(mp.Y)] if rot_angle == 0 else [])

sim.run(until=100)
sim.run(until=20)

nonpml_vol = mp.Volume(center=mp.Vector3(), size=mp.Vector3(10,10,0))

sim.plot2D(fields=mp.Ez,
plot_boundaries_flag=False,
output_plane=nonpml_vol)

if mp.am_master():
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