In a side-by-side comparison using 1.6 Tb/s ports, optical cables can consume up to 20 watts of power, vs. virtually none for copper.
That gap has major implications at scale. In massive AI installations with thousands of connections, optical power draw can quickly add up to a meaningful share of a facility’s total energy usage.
Despite its efficiency, copper has a hard physical limitation: distance. As data rates increase, the maximum length of passive copper cables shrinks dramatically.
At common speeds—such as 1Gb/s—copper Ethernet cables can span long distances without issue. But at the speeds used inside AI systems, the story changes. At roughly 200 Gb/s per lane, passive copper connections are limited to only a few meters, typically around two to three meters. Beyond that, signal integrity breaks down and fiber becomes inevitable, said Shainer.
This constraint shapes how modern data centers are built. Copper is ideal for scale‑up networking, such as connecting GPUs within the same rack, where distances are short. Scale‑out networking—linking racks across rows, halls, or entire buildings—requires fiber optics.
Fiber also matches copper in raw speed potential. Both media can support extremely high data rates, but fiber maintains those speeds over vastly longer distances. The tradeoff is higher cost, greater fragility, and significantly higher power consumption. Copper cables are physically tough and difficult to damage. Fiber cables contain delicate glass strands that can break if bent or mishandled.
