Silicon Photonics

Co-packaged silicon photonics is the networking technology that makes rack-scale AI compute physically possible. In the Vera Rubin platform, NVIDIA's Spectrum-6 Ethernet switch integrates silicon photonics directly into the switch package, delivering 102.4 Tb/s per switch with a 64x improvement in signal integrity over conventional electrical interconnects.

Traditional copper-based interconnects hit fundamental limits at the bandwidth densities required for rack-scale AI. Signal degradation, power consumption, and thermal challenges all compound as data rates increase. Silicon photonics solves this by converting electrical signals to light at the chip package boundary, transmitting optically within the rack, and converting back at the destination. The result is dramatically higher bandwidth at lower power per bit, with signal integrity that scales rather than degrades with distance.

For the NVL72 rack, silicon photonics enables the 260 TB/s aggregate bandwidth across 72 GPUs. Without optical interconnects, the cableless modular tray design — where trays connect via blind-mate connectors rather than cables — would not be feasible at these data rates.

Key Claims

• 102.4 Tb/s per Spectrum-6 switch — Co-packaged silicon photonics integrated at the switch level. Evidence: strong (NVIDIA Vera Rubin)
• 64x signal integrity improvement — Over conventional electrical interconnects. Evidence: strong (NVIDIA Vera Rubin)
• Enables cableless rack design — Optical interconnects make blind-mate tray connectors viable at rack-scale bandwidth. Evidence: moderate (inferred) (NVIDIA Vera Rubin)

Open Questions

• What are the yield challenges for co-packaged silicon photonics at scale production?
• How does the cost premium compare to conventional electrical interconnects, and when does it cross over?
• Can competing rack-scale architectures (hyperscaler ASICs) adopt silicon photonics independently of NVIDIA?
• What is the power savings per bit versus copper at these data rates?

Related Concepts

• Rack-Scale AI Compute — The system architecture that silicon photonics enables

Backlinks

Pages that reference this concept:

• NVIDIA Vera Rubin Platform