Bragg grating — transmission and reflection stopband#
validated · 2026-08-28
This case compares a local FDTDX result with pinned reference data generated by Tidy3D. The originating Tidy3D example is BraggGratings.ipynb, pinned at commit c37c785d52e9.
Parameters → exact geometry → voxelized material → local FDTDX run → simulated field → quantitative analysis. Every code cell and retained output is visible, and the .ipynb source is downloadable.
This page is the compact benchmark record. The linked notebook is the primary scientific documentation and contains the actual simulation evidence.
What is exercised#
Twenty-four 324 nm periods form a side-corrugated silicon guide. The three wavelengths sample both shoulders and the 1.532 um stopband. The reflection monitor lies in the uniform access guide rather than intersecting a tooth, and the connected grating is rasterized as one polygon on a 25 nm grid.
This case runs at its declared full benchmark resolution (resolution factor 1.0).
Reconstruction choices#
The official device dimensions, material stack, excitations, and measured observable are retained where they determine the physics. The local scene uses 416 × 136 × 72 cells and the common port/source normalization machinery. The shared energy-decay cutoff stopped the run after 16,811 of 62,940 allowed steps. Geometry is rasterized as connected material before placement when touching polygons would otherwise introduce grid-snapping seams.
The field panel above is explicitly a schematic of the device and propagation path. The curves and scalar values in the result panel are executed benchmark outputs: solid circles are FDTDX; dashed crosses are the frozen Tidy3D reference.
Recorded result#
Metric |
Observed / error |
Reference / limit |
Error |
Effective budget |
Result |
|---|---|---|---|---|---|
|
0.0790785 |
0.12 |
0.0790785 |
0.12 |
PASS |
|
0.107065 |
0.12 |
0.107065 |
0.12 |
PASS |
|
0.0199027 |
0.05 |
0.0199027 |
0.05 |
PASS |
The table is rendered from progress.json; it is not a hand-written success claim. For metrics that report an error directly, the “observed” column repeats that error and the reference column is the acceptance threshold.
Reproduce#
uv run fdtdx-bench run --case device_bragg_grating
Implementation and provenance: benchmarks/cases/device_bragg_grating/case.yaml, benchmarks/cases/device_bragg_grating/run.py, benchmarks/goldens/device_bragg_grating.npz.