The AI Interconnect War: Copper Fights Back Against Optics

Key Takeaways

• AI clusters demand higher bandwidth, lower latency intra‑rack links.
• DAC limited to ~1 m; AEC reaches 2‑2.5 m with DSP.
• AEC offers best cost‑power‑distance trade‑off for 800G.
• Optical CPO promising but not commercially viable before 2028.
• Power consumption drives shift from copper to smarter active cables.

Summary

The post examines the escalating demand for short‑reach interconnects as AI models grow larger and data centers shift to massive GPU clusters. It compares copper‑based options—DAC, ACC, and AEC—with optical solutions like AOC and emerging Co‑Packaged Optics (CPO). Active Electrical Cable (AEC) is highlighted as the current sweet spot, delivering 400G/800G speeds over 2‑2.5 m with low power and reasonable cost. The article also notes that CPO’s widespread adoption is unlikely before 2027‑2029.

Pulse Analysis

The rapid expansion of AI workloads has turned the once‑overlooked in‑rack interconnect into a performance bottleneck. Modern training clusters stitch together hundreds of GPUs, generating petabytes of data that must traverse a few centimeters between boards at terabit‑per‑second rates. Traditional PCB traces and passive copper cables cannot sustain the required signal integrity, prompting a reevaluation of how data moves inside a rack. Operators now prioritize solutions that combine high bandwidth density with minimal latency and power draw, as every millisecond saved translates into faster model convergence and lower electricity bills.

Among the copper‑based families, Active Electrical Cable (AEC) stands out because it embeds digital signal processors at both ends, actively correcting insertion loss, crosstalk, and reflection. This DSP‑driven approach extends reliable reach to roughly 2‑2.5 meters while keeping power consumption under 3 watts per 1.6 Tbps link—significantly better than the 2.5 W of Active Copper Cable (ACC) and far more cost‑effective than Active Optical Cable (AOC). AEC’s price point and ease of deployment make it the preferred choice for 400G and emerging 800G server racks, where density and thermal budgets are tight. By contrast, Direct Attach Copper (DAC) is now confined to sub‑meter distances, limiting its usefulness in the high‑speed AI era.

Looking ahead, Co‑Packaged Optics (CPO) promises ultra‑low energy per bit and multi‑terabit lanes, but its complex integration and high capex push mass adoption beyond 2027. In the interim, the ecosystem of cable manufacturers and silicon vendors is consolidating around AEC, driving standardization and economies of scale. Data‑center architects who adopt AEC now can capture immediate efficiency gains while positioning their infrastructure for a smoother transition to optical solutions once they become financially viable.