In this case study, we demonstrate loading a foundry PDK, performing RF and optical simulations, conducting time-domain analyses, and generating fabrication-ready layouts — all within a single interface. The example features an ultra-high-speed electro-optic modulator in thin-film lithium niobate (TFLN).

Background

Electro-optic Mach-Zehnder modulators (EO-MZMs) are essential in photonic integrated circuits (PICs), particularly for high-speed optical communication. These devices modulate light by changing the refractive index of a waveguide in response to an applied electric field—a process that requires careful coordination of electrical and optical properties.

Designing such devices traditionally involves fragmented workflows: separate tools for layout, electrostatic modeling, optical simulation, and data analysis. These disconnected steps can lead to inefficiencies, longer development cycles, and integration errors.

Explore the complete example:  Electro-Optic MZM Example in PhotonForge Documentation

Challenges

To design and optimize EO-MZMs, engineers need to:

• Accurately simulate the electro-optic effect, including voltage-induced refractive index changes.

• Understand the interaction between RF electrodes and optical waveguides.

• Quantify performance metrics like extinction ratio, insertion loss, and phase modulation efficiency.

• Iterate rapidly on device geometry, electrode configuration, and material stack-up—all while ensuring fabrication readiness.

Traditional limitations:

• Separate solvers for electrical and optical domains make co-simulation cumbersome.

• Manual data exchange between tools increases the chance of error.

• High computational costs due to 3D field simulations.

• Limited layout-driven simulation capabilities inhibit rapid prototyping.

Solution with PhotonForge

PhotonForge unifies layout, electrostatic, and full-wave optical simulation within one cohesive platform. Using the Tidy3D engine, PhotonForge allows for:

• Electro-optic co-simulation using voltage-dependent permittivity mapping

• GPU-accelerated FDTD simulation for rapid optical modeling

• Scriptable Python interface for parameter sweeps and design automation

• Drag-and-drop layout tools for fast, fabrication-aligned design creation

• Direct GDS import/export for seamless foundry integration

• 3D field visualization of electric and optical field distributions

Design details

The EO-MZM design in this case study includes:

• Y-splitter: An input waveguide splits the optical signal into two arms.
  

• Phase modulator arms: Each arm contains a straight waveguide surrounded by metal electrodes. A voltage applied to these electrodes induces an electric field that modifies the local refractive index.
  

• Whole device: Integrate the edge couplers with the MZM and create a complete device.
  

Simulation process

1. Layout construction:
   The entire modulator geometry, including optical waveguides, cladding layers, and electrode geometries, is created in PhotonForge using its layout editor or scriptable Python interface.
   

2. RF photonic solver:
   PhotonForge calculates the electric field distribution generated by the applied voltage. From this field, the change in refractive index is computed using the linear electro-optic (Pockels) effect for the selected material (e.g., LiNbO₃, silicon, etc.).
   

3. Permittivity mapping:
   The induced index change is transformed into a spatially varying permittivity map, which is then used to perturb the optical domain for accurate co-simulation.

4. FDTD Simulation:
   The perturbed structure is simulated using Tidy3D’s GPU-accelerated FDTD solver to analyze how the modulated index distribution affects light propagation.

5. Result analysis:
   The output fields are analyzed to determine: insertion loss, extinction ratio (ER), phase shift efficiency, and output intensity modulation vs. input voltage.

Results

Using PhotonForge, the simulated EO-MZM achieved:

• High extinction ratio: ~20–30 dB depending on phase mismatch

• Insertion loss: Maintained below 1 dB with optimized tapers

• π-phase shift voltage-length product (VπL): Tunable via electrode spacing and material selection

A full 3D model's complete co-simulation runtime is under 10 minutes. The in-built visualization tools provide 3D overlays of both the optical and electric fields, enabling intuitive debugging and optimization. Cross-sectional slices and field animations provide insights into wave interference dynamics and loss mechanisms.

Advantages Over Traditional Tools

Conclusion

This case study illustrates how PhotonForge transforms the workflow for designing and simulating electro-optic modulators. With a unified environment that supports full electro-optic co-simulation, high-performance GPU-based FDTD solvers, and fabrication-ready layouts, engineers can now:

• Rapidly iterate on device concepts

• Confidently evaluate performance

• Streamline handoff to fabrication

Whether you're developing cutting-edge optical interconnects or optimizing modulators for quantum applications, PhotonForge allows you to move faster, with accuracy and confidence.

Explore the example

Electro-Optic MZM Example in PhotonForge Documentation