SPIPE: Differentiable SPICE-Level Co-Simulation Program for Integrated Photonics and Electronics

Heterogeneous photonic-electronic systems, such as co-packaged optics and photonic-electronic artificial intelligence (AI) accelerators, are rapidly gaining traction but also pose significant design challenges due to distinct design methodologies. Digital and analog electronics are typically described using hardware description languages and SPICE, respectively, whereas photonic devices and systems are represented using permittivity tensors on the Yee grid and the Scattering matrix formulation. This disparity necessitates an end-to-end photonic-electronic cosimulation tool to streamline co-design. Most preliminary cosimulation approaches rely on translating photonic compact models into Verilog-A or SPICE models to simulate everything there, which not only introduces the additional complexity of model conversion but also has potential numerical stability problems. Additionally, another critical functionality missing from the current implementation is enabling gradient calculation in these co-simulators, which will be crucial for end-to-end gradient-based electronic-photonic system optimization. To address these challenges, we introduce SPIPE, a differentiable SPICE-level co-simulation framework for integrated photonic-electronic systems. SPIPE is the first co-simulator to overcome model conversion issues and to provide differentiability. Numerical experiments on several circuits confirm the accuracy of SPIPE when compared to analytical solutions and real-world experimental data. Furthermore, in cases where existing simulators are applicable, SPIPE achieves a runtime reduction of 2!+85!A compared to an industry-standard simulator. SPIPE features an integrated simulation interface with a low usage barrier, opening avenues for more accessible and effective photonic-electronic co-design. SPIPE is open sourced: https://github.com/zhengqigao/spipe.