ECOC 2025 Tech Spotlight: Synopsys on the Role of 448G Electrical Interfaces in AI Network Optics

Introduction

Talking about electrical interfaces at an optics conference may seem a little out of place, but in reality optics and electrical interfaces are tightly coupled. Whether it is pluggable optical modules, CPO (Co-Packaged Optics), or future chiplet-based architectures, all of them rely on high-speed electrical interfaces to carry signals into and out of the optical engine.

In its ECOC 2025 talk, Synopsys pointed out that the 448G electrical interface will be a key inflection point for AI networks, because it simultaneously determines the trade-offs in modulation format, FEC coding, reach, and optical module design.

Content

1. Why Do Electrical Interfaces Still Matter?

• Functional role: Even if everything eventually goes optical, the electrical interface remains the essential bridge between the GPU/ASIC and the optical module.

• AI network requirements:

  • Scale-up: In-rack GPU-to-GPU links require ultra-low latency and high radix (large-scale direct connectivity).

  • Scale-out: Cross-rack and cross-hall links require longer reach and high reliability.

• Challenge: Copper reach keeps shrinking, from 7m → 5m → 3m → 2m → 1m. Optics must step in, but the electrical interface remains central to overall performance.

2. Why 448G Is Hard

• Harder than 200G: Signal integrity, packaging, and trace loss requirements are far more stringent.

• Modulation format:

  • IMDD optics have converged on PAM4.

  • The electrical side is still debating: PAM4, or PAM6/PAM8? Different modulation choices affect FEC and system latency.

• Impact on FEC:

  • Historically, the optical side has generally adopted the FEC defined by the electrical side (e.g., RS-FEC).

  • In the 448G era, new FEC codes may be needed to balance bit error rate, latency, and power.

3. The Evolution Path of Electrical Interconnects

• Passive copper cables (DAC): Lowest power, but reach is under 1m.

• Active copper cables (ACC/AEC): Extend reach with re-drivers or re-timers, at the cost of added power.

• Co-Packaged Copper: Seen as an "inevitable option" that shortens electrical traces and lowers loss within CPO architectures.

👉 Conclusion: Electrical interfaces will not disappear; instead, they are shifting toward a role that is short-reach, high-performance, and tightly coupled with optics.

4. Electro-Optical Co-Design

• Gearbox approach: Two 200G lanes → one 400G lane. Mature, but with limited efficiency.

• The extreme CPO vision: All electrical interfaces disappear and photonic chiplets take over entirely, but this requires a massive architectural shift.

• The realistic outcome: A hybrid architecture (pluggable + CPO + co-packaged copper) that requires joint electrical-optical optimization.

5. Key Challenges Ahead

• Modulation and coding choices: PAM4/PAM6/PAM8 and their corresponding FEC.

• Simpler electrical interfaces: As optics move closer to the ASIC, electrical channels get shorter and system design becomes easier, but new packaging technologies are needed.

• Materials outlook: CMOS still dominates today, but breaking through future limits may require compound semiconductors (such as InP/GaAs).

Summary

Synopsys' perspective reveals that:

1. 448G electrical interfaces are an unavoidable challenge, considerably harder than 200G.

2. Electrical and optical are tightly coupled, jointly determining the direction of modulation, FEC, and optical module design.

3. Hybrid interconnects will persist for the long term: passive/active copper, pluggables, and CPO will coexist, chosen according to the application.

4. Electro-optical co-design is the way forward: not a single technology, but system-level integration.

5. Materials innovation still lies ahead: silicon can carry on for now, but compound semiconductors may be needed in the long run.

Overall, Synopsys reminded the industry that the bottleneck of AI networks lies not only in optics, but at the electrical-optical boundary. The 448G electrical interface will be a key cornerstone in determining whether next-generation data centers can smoothly move to 1.6T/3.2T.