The Copper Cliff and the Rise of Alternative Interconnects

For years, scaling out has largely relied on photonic chips and optical fiber, capable of transmitting data over long distances. Scaling up, however, has traditionally depended on copper cables, a simpler and more cost-effective solution for short-range, high-bandwidth connections. But as the demand for GPU-to-GPU bandwidth surges – Nvidia anticipates an eightfold increase to 576 GPUs per system by 2027 – copper is reaching its breaking point. This challenge is now widely known within the industry as the “copper cliff.”

David Kuo, Vice President of Product Marketing and Business Development at Point2 Technology, explains that as data rates climb into the terabit-per-second realm, the physical properties of copper necessitate thicker wires and increased power consumption. This creates significant congestion within already crowded server racks, hindering further scaling. The industry is exploring solutions like active electrical cables (AECs) with retimers to extend copper’s reach, but these come with their own complexities and power demands.

Radio Waves: A Disruptive New Approach

Enter Point2 Technology and AttoTude, two startups proposing a radical alternative: replacing copper with radio waves. Their approach promises to deliver the low cost and reliability of copper, combined with the reach of optical fiber, without the associated drawbacks. Instead of transmitting data as electrical signals through metal, they modulate data onto radio frequencies and transmit it through waveguides.

Point2 is developing a 1.6-terabit-per-second cable utilizing eight polymer waveguides, each capable of carrying 448 gigabits per second at 90 GHz and 225 GHz. AttoTude is pursuing a similar concept, but at even higher terahertz frequencies and with a different cable design. Both companies claim their technologies offer significant advantages: longer reach (10-20 meters), lower power consumption (one-third that of optical solutions, in Point2’s case), and reduced cost.

“Customers love fiber. But what they hate is the photonics,” says Dave Welch, founder and CEO of AttoTude, a veteran of optical telecom equipment manufacturing. “Electronics have been demonstrated to be inherently more reliable than optics.” Welch’s background at Infinera, recently acquired by Nokia for $2.3 billion, underscores the potential for disruption in this space.

The Science Behind the Shift: Overcoming the Skin Effect

The limitations of copper stem from a phenomenon known as the “skin effect.” At high frequencies, electrical current tends to flow along the surface of the wire, increasing resistance and signal loss. This necessitates wider wires and more power to maintain signal integrity. Radio frequencies, with their longer wavelengths, are less susceptible to the skin effect, allowing for narrower cables and reduced power consumption.

Point2’s technology leverages standard 28-nanometer CMOS manufacturing processes, making it relatively easy and cost-effective to produce. This contrasts sharply with the precision manufacturing required for optical interconnects, which can be prone to reliability issues – a phenomenon known as “link flap.”

Don Barnetson, Senior Vice President and Head of Product at Credo, acknowledges the challenges with copper but emphasizes the industry’s continued reliance on it. “You start with passive copper, and you do everything you can to run in passive copper as long as you can.” However, he concedes that physics will eventually necessitate alternative solutions.

But what will it take for these new technologies to gain widespread adoption? Will the industry embrace a fundamentally different approach to data transmission, or will incremental improvements to existing copper-based systems suffice? And how will these advancements impact the overall architecture of data centers, particularly in relation to cooling and power distribution?

The potential for radio-based interconnects extends beyond simply replacing copper. Both Point2 and AttoTude are exploring the possibility of integrating their technology directly onto GPUs, potentially eliminating the need for intermediate cabling altogether. This co-packaged approach could further reduce latency, improve energy efficiency, and unlock new levels of performance.

The race is on to overcome the limitations of current data transmission technologies and pave the way for the next generation of AI infrastructure. The future of AI may very well depend on our ability to move data faster, more efficiently, and more reliably.

Frequently Asked Questions

• What is the “copper cliff” in the context of AI infrastructure?

  The “copper cliff” refers to the physical limitations of copper cabling as data rates increase. Higher data rates require thicker wires and more power, making it increasingly difficult to scale up computing systems.

• How do Point2 and AttoTude’s radio-based cables address the challenges of copper?

  Point2 and AttoTude utilize radio frequencies to transmit data, which are less susceptible to signal loss and allow for narrower cables and lower power consumption compared to copper.

• What are the potential benefits of co-packaging radio transceivers with GPUs?

  Co-packaging could significantly reduce latency, improve energy efficiency, and simplify the overall system architecture by eliminating the need for external cabling.

• What is the skin effect and how does it impact copper cables?

  The skin effect causes electrical current to flow primarily along the surface of a conductor at high frequencies, increasing resistance and signal loss. This necessitates thicker wires and more power for copper cables.

• How does the reliability of radio-based interconnects compare to optical fiber?

  Proponents of radio-based interconnects argue that they offer greater reliability than optical fiber due to the inherent robustness of electronic components and simpler manufacturing processes.