Cornerstone Forge

This Python module implements the open-source Cornerstone PDK (University of Southampton silicon photonics MPW foundry) as components and technology specifications for PhotonForge.

The current release ships the Si_220nm_passive platform:

• 9 GDS layers (Si etches, heater filament, contact pads, info)
• 4 PortSpecs (strip 1310 / strip 1550 / rib 1310 TE / rib 1550 TE)
• 6 ExtrusionSpecs covering the full Si stack including grating shallow etches
• 29 fixed-geometry GDS components (waveguides, MMIs, bends, crossings, grating couplers, MZIs, heater, packaging template) loaded with ports attached from the foundry's YAML metadata

Additional Cornerstone platforms (Si_220nm_active, Si_340nm, Si_500nm, SiN_300nm, SiN_200nm, Ge_on_Si, Si_sus_*) are planned for a future release.

Installation

Python interface

pip install cornerstone-forge

Usage

import photonforge as pf
import cornerstone_forge as cf

# Activate the Si_220nm_passive technology
tech = cf.si220_passive()
pf.config.default_technology = tech

# List the components shipped with the PDK
print(cf.list_components())

# Load a foundry GDS cell with ports attached from its YAML metadata
mmi = cf.component("SOI220nm_1550nm_TE_STRIP_2x1_MMI")

# Layout-only in this release: an empty Tidy3DModel is attached and
# component.s_matrix(...) will run FDTD on demand. Pre-baked compact /
# S-parameter models are planned for a future release.

The included notebooks/technology_demo.ipynb walks through layers, extrusions, port specs, and stack-up cross sections. notebooks/component_demo.ipynb shows GDS loading, port inspection, cross sections, and 3D rendering.

What's loaded vs. what isn't

The Cornerstone PDK ships fixed-geometry GDS cells with YAML metadata (no parametric APIs). Each component carries:

• Optical ports: pf.Port on the strip / rib cross-section spec named in the YAML, with input_direction flipped from the YAML's orientation so the port arrow points into the device (the direction light enters).
• Heater contacts: pf.Terminal on the contact-pad layer, sized to match the actual contact-pad polygon in the GDS.
• Grating-coupler fiber side: pf.GaussianPort placed above the top oxide, tilted by the coupling_angle_cladding from the YAML.

The Si_Etch2_DF_120nm and Floorplan / Label_Etch_DF info layers are declared in the technology but pass through round-trip without participating in the Si extrusion stack.

Limitations

• Si_220nm_passive only — other Cornerstone platforms not yet implemented.
• Layout-only; no foundry-curated S-parameter models attached.
• Cornerstone publishes refractive-index data for Si and SiO2 in the source repo. The default media here come from tidy3d.material_library (Li1993 Si, Palik SiO2) for compatibility with other PhotonForge PDKs; using the Cornerstone CSVs directly is on the roadmap.
• TiN heater filament uses Ti from the material library as a placeholder.

License

MIT — see LICENSE.