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Merged
vvahidd merged 1 commit into from
Jul 25, 2026
Merged

docs: fix mode-solver plot titles and add TFLN band diagram #198

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153 changes: 78 additions & 75 deletions nbs/meep_mode_solver_rib.ipynb
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39 changes: 21 additions & 18 deletions nbs/meep_mode_solver_rib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,18 +13,18 @@
# name: python3
# ---

# %% [markdown] papermill={"duration": 0.002045, "end_time": "2026-07-24T11:58:07.011380", "exception": false, "start_time": "2026-07-24T11:58:07.009335", "status": "completed"}
# %% [markdown] papermill={"duration": 0.004561, "end_time": "2026-07-24T12:40:26.368993", "exception": false, "start_time": "2026-07-24T12:40:26.364432", "status": "completed"}
# # Mode Solver — Rib Waveguide (meep)
#
# Fundamental TE mode of a silicon rib waveguide: ``n_eff`` + 2D (Y, Z) field profile.
#
# **Cross-section:** SiO2 box / Si slab 70 nm / Si rib 150 nm (total 220 nm).
# Lateral confinement via effective-index contrast.

# %% [markdown] papermill={"duration": 0.000842, "end_time": "2026-07-24T11:58:07.013311", "exception": false, "start_time": "2026-07-24T11:58:07.012469", "status": "completed"}
# %% [markdown] papermill={"duration": 0.002244, "end_time": "2026-07-24T12:40:26.374021", "exception": false, "start_time": "2026-07-24T12:40:26.371777", "status": "completed"}
# ### Imports

# %% papermill={"duration": 1.906519, "end_time": "2026-07-24T11:58:08.920596", "exception": false, "start_time": "2026-07-24T11:58:07.014077", "status": "completed"}
# %% papermill={"duration": 1.707128, "end_time": "2026-07-24T12:40:28.083026", "exception": false, "start_time": "2026-07-24T12:40:26.375898", "status": "completed"}
import gdsfactory as gf
import matplotlib.pyplot as plt
import numpy as np
Expand All @@ -36,10 +36,10 @@

gf.gpdk.PDK.activate()

# %% [markdown] papermill={"duration": 0.000755, "end_time": "2026-07-24T11:58:08.922376", "exception": false, "start_time": "2026-07-24T11:58:08.921621", "status": "completed"}
# %% [markdown] papermill={"duration": 0.000709, "end_time": "2026-07-24T12:40:28.084875", "exception": false, "start_time": "2026-07-24T12:40:28.084166", "status": "completed"}
# ### Build the GDS component

# %% papermill={"duration": 0.006301, "end_time": "2026-07-24T11:58:08.929378", "exception": false, "start_time": "2026-07-24T11:58:08.923077", "status": "completed"}
# %% papermill={"duration": 0.006569, "end_time": "2026-07-24T12:40:28.092129", "exception": false, "start_time": "2026-07-24T12:40:28.085560", "status": "completed"}
SLAB_WIDTH = 3.0 # um
RIB_WIDTH = 0.5 # um
LENGTH = 10.0 # um
Expand Down Expand Up @@ -69,10 +69,10 @@
print(f" Ports: {[p.name for p in c.ports]}")
print(f" Layers: {list(c.layers)}")

# %% [markdown] papermill={"duration": 0.00074, "end_time": "2026-07-24T11:58:08.931019", "exception": false, "start_time": "2026-07-24T11:58:08.930279", "status": "completed"}
# %% [markdown] papermill={"duration": 0.000703, "end_time": "2026-07-24T12:40:28.093695", "exception": false, "start_time": "2026-07-24T12:40:28.092992", "status": "completed"}
# ### Layer stack

# %% papermill={"duration": 0.003585, "end_time": "2026-07-24T11:58:08.935300", "exception": false, "start_time": "2026-07-24T11:58:08.931715", "status": "completed"}
# %% papermill={"duration": 0.003555, "end_time": "2026-07-24T12:40:28.097911", "exception": false, "start_time": "2026-07-24T12:40:28.094356", "status": "completed"}
layers = {
"ox": Layer(
name="box",
Expand Down Expand Up @@ -110,10 +110,10 @@
f" {name:6s} z=[{l.zmin:+.3f}, {l.zmax:+.3f}] t={l.thickness:.3f} material={l.material}"
)

# %% [markdown] papermill={"duration": 0.000739, "end_time": "2026-07-24T11:58:08.937474", "exception": false, "start_time": "2026-07-24T11:58:08.936735", "status": "completed"}
# %% [markdown] papermill={"duration": 0.000703, "end_time": "2026-07-24T12:40:28.099909", "exception": false, "start_time": "2026-07-24T12:40:28.099206", "status": "completed"}
# ### Solve

# %% papermill={"duration": 104.636625, "end_time": "2026-07-24T11:59:53.574787", "exception": false, "start_time": "2026-07-24T11:58:08.938162", "status": "completed"}
# %% papermill={"duration": 174.673569, "end_time": "2026-07-24T12:43:22.774141", "exception": false, "start_time": "2026-07-24T12:40:28.100572", "status": "completed"}
WAVELENGTH = 1.55 # um
RESOLUTION = 64
PML_THICKNESS = 1 * WAVELENGTH
Expand Down Expand Up @@ -153,20 +153,20 @@
for comp, arr in mode.fields.items():
print(f" {comp}: shape={arr.shape} |max|={np.abs(arr).max():.6f}")

# %% [markdown] papermill={"duration": 0.001324, "end_time": "2026-07-24T11:59:53.577025", "exception": false, "start_time": "2026-07-24T11:59:53.575701", "status": "completed"}
# %% [markdown] papermill={"duration": 0.000845, "end_time": "2026-07-24T12:43:22.776363", "exception": false, "start_time": "2026-07-24T12:43:22.775518", "status": "completed"}
# ### Index profile

# %% papermill={"duration": 0.093477, "end_time": "2026-07-24T11:59:53.671339", "exception": false, "start_time": "2026-07-24T11:59:53.577862", "status": "completed"}
# %% papermill={"duration": 0.101406, "end_time": "2026-07-24T12:43:22.878556", "exception": false, "start_time": "2026-07-24T12:43:22.777150", "status": "completed"}
mode.plot_index(show=True)


# %% [markdown] papermill={"duration": 0.000954, "end_time": "2026-07-24T11:59:53.673436", "exception": false, "start_time": "2026-07-24T11:59:53.672482", "status": "completed"}
# %% [markdown] papermill={"duration": 0.000938, "end_time": "2026-07-24T12:43:22.881329", "exception": false, "start_time": "2026-07-24T12:43:22.880391", "status": "completed"}
# ### Mode profile (interactive)
#
# ``|field|`` maps for every component with zoom / pan / hover. Axes use equal
# aspect so the cross-section is physically proportioned.

# %% papermill={"duration": 0.203272, "end_time": "2026-07-24T11:59:53.877703", "exception": false, "start_time": "2026-07-24T11:59:53.674431", "status": "completed"}
# %% papermill={"duration": 0.232122, "end_time": "2026-07-24T12:43:23.114292", "exception": false, "start_time": "2026-07-24T12:43:22.882170", "status": "completed"}
import plotly.graph_objects as go
from plotly.subplots import make_subplots

Expand Down Expand Up @@ -197,7 +197,7 @@
cols=3,
subplot_titles=[f"|{c}|" for c in comps],
horizontal_spacing=0.08,
vertical_spacing=0.12,
vertical_spacing=0.2,
)

for i, comp in enumerate(comps):
Expand Down Expand Up @@ -231,11 +231,14 @@
)

fig.update_layout(
height=550,
height=650,
autosize=True,
title_text=(
f"Rib waveguide fundamental TE mode "
f"(lambda={WAVELENGTH:.2f} µm, n_eff={mode.n_eff:.4f})"
margin=dict(t=70, b=60),
title=dict(
text=f"lambda={WAVELENGTH:.2f} µm, n_eff={mode.n_eff:.4f}",
x=0.5,
xanchor="center",
font=dict(size=13),
),
)
fig.show(config={"responsive": True})
639 changes: 561 additions & 78 deletions nbs/meep_mode_solver_tfln.ipynb
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192 changes: 173 additions & 19 deletions nbs/meep_mode_solver_tfln.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@
# name: python3
# ---

# %% [markdown] papermill={"duration": 0.003127, "end_time": "2026-07-24T12:00:00.754624", "exception": false, "start_time": "2026-07-24T12:00:00.751497", "status": "completed"}
# %% [markdown] papermill={"duration": 0.006539, "end_time": "2026-07-24T16:33:50.087547", "exception": false, "start_time": "2026-07-24T16:33:50.081008", "status": "completed"}
# # Mode Solver — TFLN Ridge Waveguide (meep)
#
# Fundamental TE mode of thin-film lithium niobate ridge waveguide at lambda=1.55 µm.
Expand All @@ -25,10 +25,10 @@
# **Expected:** n_eff ~ 1.85, n_group ~ 2.20.
# ``background_material="sio2"`` fills unpatterned space with SiO2.

# %% [markdown] papermill={"duration": 0.001785, "end_time": "2026-07-24T12:00:00.758676", "exception": false, "start_time": "2026-07-24T12:00:00.756891", "status": "completed"}
# %% [markdown] papermill={"duration": 0.002776, "end_time": "2026-07-24T16:33:50.095297", "exception": false, "start_time": "2026-07-24T16:33:50.092521", "status": "completed"}
# ### Imports

# %% papermill={"duration": 1.835389, "end_time": "2026-07-24T12:00:02.595708", "exception": false, "start_time": "2026-07-24T12:00:00.760319", "status": "completed"}
# %% papermill={"duration": 7.319947, "end_time": "2026-07-24T16:33:57.417774", "exception": false, "start_time": "2026-07-24T16:33:50.097827", "status": "completed"}
import gdsfactory as gf
import matplotlib.pyplot as plt
import numpy as np
Expand All @@ -40,7 +40,7 @@

gf.gpdk.PDK.activate()

# %% [markdown] papermill={"duration": 0.001066, "end_time": "2026-07-24T12:00:02.598170", "exception": false, "start_time": "2026-07-24T12:00:02.597104", "status": "completed"}
# %% [markdown] papermill={"duration": 0.004634, "end_time": "2026-07-24T16:33:57.427896", "exception": false, "start_time": "2026-07-24T16:33:57.423262", "status": "completed"}
# ### LiNbO3 material (Zelmon 1997)
#
# LiNbO3 is birefringent and is now registered as a uniaxial material
Expand All @@ -60,10 +60,10 @@
# extraordinary axis (zz).


# %% [markdown] papermill={"duration": 0.001125, "end_time": "2026-07-24T12:00:02.600276", "exception": false, "start_time": "2026-07-24T12:00:02.599151", "status": "completed"}
# %% [markdown] papermill={"duration": 0.0038, "end_time": "2026-07-24T16:33:57.436203", "exception": false, "start_time": "2026-07-24T16:33:57.432403", "status": "completed"}
# ### Build the GDS component

# %% papermill={"duration": 0.00652, "end_time": "2026-07-24T12:00:02.608029", "exception": false, "start_time": "2026-07-24T12:00:02.601509", "status": "completed"}
# %% papermill={"duration": 0.174397, "end_time": "2026-07-24T16:33:57.625614", "exception": false, "start_time": "2026-07-24T16:33:57.451217", "status": "completed"}
SLAB_WIDTH = 5.0 # um --- wide slab
CORE_WIDTH = 1.1 # um --- w0 from reference design
LENGTH = 10.0 # um --- waveguide length (arbitrary for mode solving)
Expand Down Expand Up @@ -101,12 +101,12 @@
print(f" Ports: {[p.name for p in c.ports]}")
print(f" Layers: {list(c.layers)}")

# %% [markdown] papermill={"duration": 0.001177, "end_time": "2026-07-24T12:00:02.611178", "exception": false, "start_time": "2026-07-24T12:00:02.610001", "status": "completed"}
# %% [markdown] papermill={"duration": 0.003233, "end_time": "2026-07-24T16:33:57.635212", "exception": false, "start_time": "2026-07-24T16:33:57.631979", "status": "completed"}
# ### Layer stack
#
# SiO2 fills background via ``background_material="sio2"``.

# %% papermill={"duration": 0.005052, "end_time": "2026-07-24T12:00:02.617336", "exception": false, "start_time": "2026-07-24T12:00:02.612284", "status": "completed"}
# %% papermill={"duration": 0.016785, "end_time": "2026-07-24T16:33:57.660454", "exception": false, "start_time": "2026-07-24T16:33:57.643669", "status": "completed"}
SLAB_THICKNESS = 0.22 # um (h3)
CORE_THICKNESS = 0.40 # um --- total LiNbO3 thickness
RIDGE_THICKNESS = CORE_THICKNESS - SLAB_THICKNESS # 0.18 um
Expand Down Expand Up @@ -150,10 +150,10 @@
f"t={l.thickness:.3f} material={l.material} gds={l.gds_layer}"
)

# %% [markdown] papermill={"duration": 0.00124, "end_time": "2026-07-24T12:00:02.619810", "exception": false, "start_time": "2026-07-24T12:00:02.618570", "status": "completed"}
# %% [markdown] papermill={"duration": 0.015262, "end_time": "2026-07-24T16:33:57.679862", "exception": false, "start_time": "2026-07-24T16:33:57.664600", "status": "completed"}
# ### Solve

# %% papermill={"duration": 80.363473, "end_time": "2026-07-24T12:01:22.984371", "exception": false, "start_time": "2026-07-24T12:00:02.620898", "status": "completed"}
# %% papermill={"duration": 1925.213727, "end_time": "2026-07-24T17:06:02.898833", "exception": false, "start_time": "2026-07-24T16:33:57.685106", "status": "completed"}
WAVELENGTH = 1.55 # um
RESOLUTION = 64 # grid points per um
PML_THICKNESS = WAVELENGTH # um
Expand Down Expand Up @@ -183,19 +183,19 @@
for comp, arr in mode.fields.items():
print(f" {comp}: shape={arr.shape} |max|={np.abs(arr).max():.6f}")

# %% [markdown] papermill={"duration": 0.001038, "end_time": "2026-07-24T12:01:22.986822", "exception": false, "start_time": "2026-07-24T12:01:22.985784", "status": "completed"}
# %% [markdown] papermill={"duration": 0.016131, "end_time": "2026-07-24T17:06:02.925467", "exception": false, "start_time": "2026-07-24T17:06:02.909336", "status": "completed"}
# ### Index profile

# %% papermill={"duration": 0.256239, "end_time": "2026-07-24T12:01:23.243947", "exception": false, "start_time": "2026-07-24T12:01:22.987708", "status": "completed"}
# %% papermill={"duration": 1.695063, "end_time": "2026-07-24T17:06:04.627531", "exception": false, "start_time": "2026-07-24T17:06:02.932468", "status": "completed"}
mode.plot_index(show=True)

# %% [markdown] papermill={"duration": 0.001004, "end_time": "2026-07-24T12:01:23.246232", "exception": false, "start_time": "2026-07-24T12:01:23.245228", "status": "completed"}
# %% [markdown] papermill={"duration": 0.004876, "end_time": "2026-07-24T17:06:04.637601", "exception": false, "start_time": "2026-07-24T17:06:04.632725", "status": "completed"}
# ### Mode profile (interactive)
#
# ``|field|`` maps for every component with zoom / pan / hover. The view is
# auto-cropped to the mode region and axes use equal aspect.

# %% papermill={"duration": 0.209603, "end_time": "2026-07-24T12:01:23.456715", "exception": false, "start_time": "2026-07-24T12:01:23.247112", "status": "completed"}
# %% papermill={"duration": 1.508412, "end_time": "2026-07-24T17:06:06.152802", "exception": false, "start_time": "2026-07-24T17:06:04.644390", "status": "completed"}
import plotly.graph_objects as go
from plotly.subplots import make_subplots

Expand Down Expand Up @@ -226,7 +226,7 @@
cols=3,
subplot_titles=[f"|{c}|" for c in comps],
horizontal_spacing=0.08,
vertical_spacing=0.12,
vertical_spacing=0.2,
)

for i, comp in enumerate(comps):
Expand Down Expand Up @@ -260,11 +260,165 @@
)

fig.update_layout(
height=550,
height=650,
autosize=True,
title_text=(
f"TFLN ridge waveguide fundamental TE mode "
f"(lambda={WAVELENGTH:.2f} µm, w0={CORE_WIDTH:.1f} µm, n_eff={mode.n_eff:.4f})"
margin=dict(t=70, b=60),
title=dict(
text=(
f"lambda={WAVELENGTH:.2f} µm, w0={CORE_WIDTH:.1f} µm, "
f"n_eff={mode.n_eff:.4f}"
),
x=0.5,
xanchor="center",
font=dict(size=13),
),
)
fig.show(config={"responsive": True})

# %% [markdown] papermill={"duration": 0.007377, "end_time": "2026-07-24T17:06:06.169543", "exception": false, "start_time": "2026-07-24T17:06:06.162166", "status": "completed"}
# ### Width sweep — band diagram
#
# Sweep the ridge width ``w0`` and track ``n_eff`` of the first few bands.
# Narrow ridges guide fewer modes, so higher-band curves appear only once the
# width is wide enough to support them. Modes below the SiO2 cladding index are
# radiative and are dropped (dashed line = cladding cutoff).
#
# Each width is an independent cloud mode-solve. Jobs are submitted in batches
# (up to ``MAX_CONCURRENT`` in flight) and waited on concurrently, so the whole
# sweep finishes in a few minutes rather than running one width at a time.

# %% papermill={"duration": 2210.842074, "end_time": "2026-07-24T17:42:57.024025", "exception": false, "start_time": "2026-07-24T17:06:06.181951", "status": "completed"}
import shutil
import tempfile
from pathlib import Path

from gsim import gcloud
from gsim.common.stack.materials import resolve_material_at_wavelength

# Snap widths to the 0.002 µm grid so gdsfactory ports stay grid-aligned.
W0_VALUES = np.round(np.linspace(0.3, 3.0, 25) / 0.002) * 0.002 # um
N_SWEEP_BANDS = 8
MAX_CONCURRENT = 10 # cloud jobs in flight at once

# SiO2 cladding index at this wavelength — guided modes must lie above it.
_clad = resolve_material_at_wavelength("sio2", WAVELENGTH)
_eps = _clad.permittivity
n_clad = float(np.sqrt(_eps if np.isscalar(_eps) else np.mean(_eps)))


def tfln_component(core_width: float) -> gf.Component:
"""Build the TFLN ridge component for a given ridge width."""
comp = gf.Component()
comp.add_polygon(
[
(-LENGTH / 2, -core_width / 2),
(LENGTH / 2, -core_width / 2),
(LENGTH / 2, core_width / 2),
(-LENGTH / 2, core_width / 2),
],
layer=(2, 0),
)
comp.add_port(
name="o1",
center=(-LENGTH / 2, 0),
width=core_width,
orientation=180,
layer=(1, 0),
)
comp.add_port(
name="o2",
center=(LENGTH / 2, 0),
width=core_width,
orientation=0,
layer=(1, 0),
)
return comp


def submit_mode_solve(core_width: float) -> str:
"""Upload + start one cloud mode-solve job (non-blocking). Returns job_id."""
sim = gm.Simulation(
geometry=gm.Geometry(component=tfln_component(core_width), stack=stack),
domain=gm.Domain(pml=PML_THICKNESS, margin_z=(0.0, 0.5)),
)
sim.mode_solver.wavelengths = [WAVELENGTH]
sim.mode_solver.first(N_SWEEP_BANDS).at_port("o1")
sim.mode_solver.y_span = SLAB_WIDTH
sim.mode_solver.background_material = "sio2" # n_field=0 -> n_eff only

tmp = Path(tempfile.mkdtemp(prefix="meep_mode_sweep_"))
try:
sim.write_mode_solver_config(tmp)
job_id = gcloud.upload(tmp, "meep", verbose=False)
gcloud.start(job_id, verbose=False)
return job_id
finally:
shutil.rmtree(tmp, ignore_errors=True)


# Submit jobs in batches so at most MAX_CONCURRENT run on the cloud at once,
# then wait for the whole batch concurrently. n_eff only (no field download).
sweep_results = [] # ModeSweepResult per width, in W0_VALUES order
for i in range(0, len(W0_VALUES), MAX_CONCURRENT):
batch = W0_VALUES[i : i + MAX_CONCURRENT]
job_ids = [submit_mode_solve(w0) for w0 in batch]
print(f"batch {i // MAX_CONCURRENT + 1}: started {len(job_ids)} jobs")
batch_results = gcloud.wait_for_results(job_ids, verbose="quiet")
if not isinstance(batch_results, list): # single-job batch returns one result
batch_results = [batch_results]
sweep_results.extend(batch_results)

# n_eff per band across the width sweep (NaN where the band is not guided).
neff_by_band = {b: [] for b in range(1, N_SWEEP_BANDS + 1)}
for w0, res in zip(W0_VALUES, sweep_results, strict=True):
found = {r.band_num: r.n_eff for r in res.at(WAVELENGTH).results}
for b in range(1, N_SWEEP_BANDS + 1):
neff = found.get(b, np.nan)
# drop radiative modes below the cladding index
neff_by_band[b].append(neff if neff > n_clad else np.nan)
guided = [b for b in range(1, N_SWEEP_BANDS + 1) if found.get(b, 0) > n_clad]
summary = ", ".join(f"b{b}={found[b]:.4f}" for b in guided)
print(f"w0={w0:.2f} µm -> {len(guided)} guided mode(s): {summary}")

# %% [markdown] papermill={"duration": 0.00381, "end_time": "2026-07-24T17:42:57.033543", "exception": false, "start_time": "2026-07-24T17:42:57.029733", "status": "completed"}
# ``n_eff`` vs ``w0`` for each band (interactive).

# %% papermill={"duration": 0.034951, "end_time": "2026-07-24T17:42:57.071777", "exception": false, "start_time": "2026-07-24T17:42:57.036826", "status": "completed"}
band_fig = go.Figure()
for b in range(1, N_SWEEP_BANDS + 1):
band_fig.add_trace(
go.Scatter(
x=W0_VALUES,
y=neff_by_band[b],
mode="lines+markers",
name=f"band {b}",
connectgaps=False,
hovertemplate="w0=%{x:.2f} µm<br>n_eff=%{y:.4f}<extra>band "
+ str(b)
+ "</extra>",
)
)
band_fig.add_hline(
y=n_clad,
line_dash="dash",
line_color="gray",
annotation_text=f"SiO2 cladding (n={n_clad:.3f})",
annotation_position="bottom right",
)
band_fig.update_layout(
height=550,
width=550,
autosize=False,
margin=dict(t=60, b=60),
xaxis_title="ridge width w0 (µm)",
yaxis_title="n_eff",
title=dict(
text=f"TFLN band diagram (lambda={WAVELENGTH:.2f} µm)",
x=0.5,
xanchor="center",
font=dict(size=13),
),
legend=dict(title=""),
)
# Fixed square aspect (width == height); no responsive stretch.
band_fig.show()
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