1x4 MMI — four-port broadband power distribution

validated · 2026-08-28

forwardresolution 1devicereal_worldpicmmisplittertidy3d_goldenofficial_notebook

This case compares a local FDTDX result with pinned reference data generated by Tidy3D. The originating Tidy3D example is MMI1x4.ipynb, pinned at commit c37c785d52e9.

Open the complete executed tutorial →

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.

1×4 MMI: broadband four-port splitting

This page is the compact benchmark record. The linked notebook is the primary scientific documentation and contains the actual simulation evidence.

What is exercised

Compact 8 x 5 um multimode section with four tapered output guides. All touching silicon is unioned before rasterization. A 30 nm grid, selected after the 40 nm grid showed resolution-sensitive port imbalance, gives about 15 cells per silicon material wavelength. The relative energy cutoff ends the 5 ps safety window automatically once the multimode tail decays.

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 516 × 283 × 63 cells and the common port/source normalization machinery. The shared energy-decay cutoff stopped the run after 28,825 of 87,417 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
out1	0.0769157	0.12	0.0769157	0.12	PASS
out2	0.0901388	0.12	0.0901388	0.12	PASS
out3	0.0472915	0.12	0.0472915	0.12	PASS
out4	0.0242981	0.12	0.0242981	0.12	PASS
total	0.0113288	0.03	0.0113288	0.03	PASS
uniformity	0.0526782	0.08	0.0526782	0.08	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_mmi_1x4

Implementation and provenance: benchmarks/cases/device_mmi_1x4/case.yaml, benchmarks/cases/device_mmi_1x4/run.py, benchmarks/goldens/device_mmi_1x4.npz.

Return to the example atlas