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README.md

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+---
+license: mit
+tags:
+  - physics
+  - electromagnetic-simulation
+  - photonics
+  - silicon-photonics
+  - fdtd
+  - pde
+size_categories:
+  - 10K<n<100K
+---
+
+# PIC-Flow Dataset
+
+22,500 frequency-domain FDTD electromagnetic-field simulations for parameterized
+silicon-on-insulator photonic devices at λ = 1.55 µm. Used as the training,
+validation, and test data for the [PIC-Flow](https://huggingface.co/RizzoLab/PIC-Flow)
+neural surrogate model.
+
+Code, documentation, and inference notebooks live in the GitHub repo:
+[Rizzo-Integrated-Photonic-Systems-Lab/PIC-Flow](https://github.com/Rizzo-Integrated-Photonic-Systems-Lab/PIC-Flow).
+
+## Contents
+
+| Path | Description |
+|---|---|
+| `shards/shard_*.npz` | Packed FDTD samples (~225 shards). Each shard contains many slots `s0/`, `s1/`, ... |
+| `shards/index.json` | Manifest mapping `(device, geometry_id, split, augment) → (shard, slot)`. |
+| `geometries.jsonl` | One line per simulated device: family, geometric parameters, port count. |
+
+## Per-sample fields
+
+Each slot inside a shard carries:
+
+| Key | Shape | Description |
+|---|---|---|
+| `eps` | `(160, 480)` float32 | Relative permittivity ε_r (Si core ≈ 5.8, SiO₂ cladding ≈ 2.09). |
+| `Ez_real`, `Ez_imag` | `(160, 480)` float32 | Real and imaginary parts of the complex E_z field, source-anchored phase. |
+| `src_mask` | `(160, 480)` float32 | Binary mask marking the active eigenmode-source port. |
+| `port_masks` | `(N_ports, 160, 480)` float32 | Per-port binary masks (e.g., 4 ports for MMIs/DCs, 3 for Y-branches). |
+| `port_ids` | `(N_ports,)` int32 | Integer port labels matching `port_masks`. |
+| `input_port` | int | Which port was excited by the eigenmode source. |
+| `wavelength_um` | float | Free-space wavelength in µm (1.55 throughout this dataset). |
+| `dx_um`, `dy_um`, `Lx_um`, `Ly_um` | float | Grid resolution and physical extent. |
+| `device` | string | Family: `mmi`, `ybranch`, or `directional_coupler`. |
+| `geometry_id`, `split` | string | Unique geometry id and `train` / `val` / `test` membership. |
+| `params/<name>` | float | Geometric parameters for this device (varies by family — see below). |
+
+## Devices and parameter sweep
+
+5-dimensional Latin-hypercube sweep per family, quantized to a half-pixel grid
+(0.025 µm at 20 pixels/µm):
+
+- **2×2 MMI** (4 ports, 7,500 samples): waveguide width [0.40–0.575], MMI width [4.5–5.5],
+  MMI length [8.0–15.0], taper width [0.575–1.5], taper length [1.0–3.0] µm.
+- **Y-branch** (3 ports, 7,500): waveguide width [0.40–0.575], junction length [1.0–3.0],
+  bend length [4.0–7.0], arm offset [0.575–2.5], output length [1.0–4.0] µm.
+- **Directional coupler** (4 ports, 7,500): waveguide width [0.40–0.575], gap [0.10–0.35],
+  coupling length [5.0–8.0], bend length [4.0–6.0], port separation [0.825–2.0] µm.
+
+## Splits
+
+Index-based, shared across all PIC-Flow ablation runs:
+
+| Split | Samples |
+|---|---|
+| train | 18,000 |
+| val | 2,250 |
+| test | 2,250 |
+
+## How to download
+
+```bash
+pip install huggingface_hub
+hf download RizzoLab/PIC-Flow-Dataset --repo-type dataset --local-dir Data/unified_sweep_mmi_ybranch_dc_7500_each_1p55um
+```
+
+The dataloader in the GitHub repo
+([`Model/dataset.py`](https://github.com/Rizzo-Integrated-Photonic-Systems-Lab/PIC-Flow/blob/main/Model/dataset.py))
+expects this layout under `Data/unified_sweep_mmi_ybranch_dc_7500_each_1p55um/`.
+
+## Generation
+
+The data was produced with the Meep FDTD solver via
+[`FDTD/unified_sweep.py`](https://github.com/Rizzo-Integrated-Photonic-Systems-Lab/PIC-Flow/blob/main/FDTD/unified_sweep.py)
+in the GitHub repo. Each sample uses an eigenmode source exciting the fundamental TE
+mode at the selected input port; fields are extracted at λ = 1.55 µm via discrete
+Fourier transforms. The vertical 220 nm SOI slab mode is pre-solved into an effective
+core index n_eff ≈ 2.4 used for the 2D scalar Helmholtz simulation.
+
+To regenerate from scratch (~24 hours on one CPU node, 16 threads):
+
+```bash
+python FDTD/unified_sweep.py --output-dir Data/ \
+    --devices mmi,ybranch,directional_coupler \
+    --num-samples 7500 --wavelengths 1.55
+```
+
+## Citation
+
+```bibtex
+@article{Quaratiello2026PICFlow,
+  author  = {Joseph Quaratiello and Anthony Rizzo},
+  title   = {Physics-Based Flow Matching for Full-Field Prediction of Silicon Photonic Devices},
+  journal = {arXiv},
+  year    = {2026}
+}
+```
+
+## License
+
+MIT.