Star Coupler Simulation

Silicon photonics design and simulation tools for star coupler circuits using gdsfactory and Lumerical MODE. This project includes automated chip layout generation and varFDTD simulation workflows.

Project Structure

Star_coupler_simulation/
├── components/              # Photonic component definitions
│   ├── star_coupler.py     # Star coupler component
│   ├── chip_layout.py      # Full chip layout generator
│   └── sharing_template_etch.gds
│
├── scripts/                 # Simulation and analysis scripts
│   ├── Run_varFDTD.py      # Automated varFDTD setup
│   ├── extract_varFDTD_results.py
│   └── plot_result.py
│
├── output/                  # Generated files
│   ├── gds/                # GDS layout exports
│   ├── lms/                # Lumerical simulation files
│   └── fsp/
│
├── docs/                    # Documentation
│   ├── GUIDE_UTILISATION.md
│   ├── CONFIGURATION.md
│   └── BUGFIXES.md
│
└── archived/                # Legacy code and tests

Installation

Requirements: Python 3.8+ and Lumerical MODE v252

pip install -r requirements.txt

Quick Start

Generate Chip Layout

Run the main chip layout generator to produce a complete GDS file:

python components/chip_layout.py

This generates a multi-circuit layout including:

• Power mode star couplers with direct routing
• Phase mode MZI characterization circuits
• Material loss calibration structures
• Waveguide loop references

Run varFDTD Simulation

For individual component characterization:

python scripts/Run_varFDTD.py

The script will:

1. Generate the star coupler geometry
2. Export GDS and launch Lumerical MODE
3. Configure the simulation structure and solver
4. Display port coordinates for manual setup

After the script completes, manually add sources and monitors in Lumerical MODE at the displayed coordinates, then run the simulation.

Extract Results

python scripts/extract_varFDTD_results.py

Results are saved to the output directory as NumPy arrays and text summaries.

Component Configuration

The star coupler parameters can be adjusted in components/star_coupler.py:

star_coupler(
    n_inputs=5,
    n_outputs=4,
    pitch_inputs=10.0,
    pitch_outputs=10.0,
    taper_length=40.0,
    wg_width=0.75,
    radius=130.0,
    layer=(4, 0)  # SiN layer
)

The chip layout circuits support phase measurement with configurable MZI parameters:

• delta_L: Path length difference for phase delay
• h1_MZI, h3_MZI: MZI arm routing parameters
• Direct SC-to-GC routing with obstacle avoidance

Simulation Notes

varFDTD: Fast 2D effective index simulation (minutes). Best for initial design iterations.

FDTD 3D: Full 3D simulation (hours). Use for final validation after varFDTD optimization.

Due to Lumerical API limitations, varFDTD port configuration requires manual setup through the GUI. The automation scripts handle geometry and solver setup only.

Troubleshooting

Port alignment issues: Check coordinates printed by Run_varFDTD.py. Ensure source/monitor spans cover the waveguide width.

Routing conflicts: The direct routing feature automatically detects and routes around MZI structures for lower star coupler outputs.

Path length errors: The route_with_loop function now includes vertical return segments in length calculations. Adjust loop_height_max if targeting long delays.

Documentation

See the docs/ folder for detailed guides:

• GUIDE_UTILISATION.md: Complete user guide
• CONFIGURATION.md: Configuration reference
• RUN_VARFDTD_IMPROVEMENTS.md: varFDTD workflow details

References

• gdsfactory: https://gdsfactory.github.io/gdsfactory/
• ubcpdk: https://gdsfactory.github.io/ubc/
• Lumerical MODE: https://optics.ansys.com/hc/en-us/