# Live folded-SiN atom-to-waveguide optimizer
running · checkpoint 2026-08-22 14:23:45 UTC
refresh in 60 s
Ey-oriented atom · 780.24 nm
single-etch 2-D mask · 241.2 nm SiN
500 nm hard atom clearance
x=0.5–4.0 µm transition fully trainable
y,z symmetry · 4× FDTD reduction
final robust binary validation pending
This campaign folds the optimized Zhang-style SiN curved mirror above and below
the atom, leaves the entire **left-hand approach channel open**, and terminates
the right side in one centered SiN waveguide. Every pixel from x=0.5 to 4.0 µm,
including the guide-shaped seed, belongs to the inverse-design region; only the
straight continuation after x=4.0 µm is fixed. The objective is the physically
normalized guided branching ratio—not a field sample—and all other closed-box
power is assigned to an explicit loss direction.
| Live quantity | Current evidence |
|---|---:|
| Guided beta | **23.6%** |
| Best evaluated beta | **26.4%** |
| Total LDOS | **1.2586× vacuum** |
| Guided LDOS | 0.29708× vacuum |
| Shifted peak LDOS (fit pending) | 1× vacuum |
| Q (fit pending) | 96.9429 |
| Pole wavelength | 781.91 nm |
| Dominant loss direction | **±z** |
| Directional loss split | -x 0.17%, +x radiation 0.00%, ±y 1.64%, ±z 98.20% |
| Inner/outer power mismatch | 5.66% |
| Output-guide modal index | 1.57004 |
| Adjoint updates | 53 / 90 |
| Independent topology pixels | 28,696 |
## Literal geometry
```{figure} ../_static/generated/folded_sin_atom_waveguide_geometry.png
:alt: Folded silicon nitride curved mirrors, central atom gap, and right output waveguide
:width: 100%
The plotted pixels are the latest geometry actually evaluated by FDTD. The
dashed circle marks 500 nm radial clearance; the stricter left access corridor
also remains air. The topology is optimized in x-y and extruded uniformly
through the slab for fabrication by one etch.
```
Geometry audit: sampled nearest-material distance
**512.652 nm**;
left access air **True**; right guide present
**True**; left guide absent **True**.
## Beta, LDOS, Q, and pole wavelength
```{figure} ../_static/generated/folded_sin_atom_waveguide_progress.png
:alt: Guided beta, atom LDOS, quality factor, and pole wavelength versus optimization update
:width: 100%
CW adjoints update beta and their finite-time LDOS diagnostic every iteration.
A separate 3.5 ps pulse ringdown periodically fits Q, wavelength, mode volume,
and shifted peak LDOS, so a beta gain cannot silently hide resonance loss or
detuning. For a high-Q seed, the shifted pole value—not a 70-period CW
transient—is the meaningful resonant LDOS.
```
## Where the light is lost
```{figure} ../_static/generated/folded_sin_atom_waveguide_losses.png
:alt: Direction-resolved non-guided optical power during optimization
:width: 100%
The +x radiation entry excludes the power assigned to the bound waveguide
mode. Symmetry-related ±y and ±z faces are restored to their physical power.
```
## Latest y-polarized electric field
```{figure} ../_static/generated/folded_sin_atom_waveguide_field.png
:alt: Ey field emitted by the atom in the folded silicon nitride coupler
:width: 100%
White contours are the literal SiN/air boundary. Only the retained y half was
simulated; this plot reconstructs the physical mirror copy for inspection.
```
## Seed provenance and optimization contract
The folded seed comes from `benchmarks/artifacts/invdes_sin_quasi2d_remote_atom_ldos_live_v1.npz` (controls SHA-256
`e297925ecd48671c71b1324ac0437069fa0660e80034a30d1169ee4a8e977d1c`). Its literal guide begins at x=1.5 µm; the
0.5–1.5 µm region is initially air but fully trainable. Before beta updates the
seed audit measured Q 9242.05,
pole wavelength 780.236 nm,
and shifted peak LDOS
4.9783× vacuum. The short CW
baseline is beta 2.911% and LDOS
1.179; it is not mislabeled as the
steady-state high-Q LDOS.
A 50 nm-radius conic feature filter, erosion/nominal/dilation sampling, and
exact-binary straight-through forward solves are used from update zero. A
geometry-only inverse-filter calibration makes the nominal projected mask
exactly equal to the literal cavity seed before FDTD. The radial 500 nm
clearance, open left approach, and terminal guide after x=4.0 µm are reimposed
after every filter/projection operation; the intervening transition is never
pinned.
The two material-specific precursor campaigns are preserved separately:
- [Silicon remote-atom shifted-LDOS campaign](paper_semi2d_ldos_dashboard.md)
- [Silicon nitride 780 nm quasi-2D campaign](sin_quasi2d_ldos_dashboard.md)
This is a live research run, not yet a validated final device. The dashboard
reports the latest evaluated design; proposed controls are not credited until
their next physical FDTD evaluation.