On December 27th, IEEE Spectrum published a blog post reporting that startups Point2 and AttoTude have developed an "active RF cable" solution using radio frequency (RF)/terahertz (THB) technology. This solution combines the low cost of copper cables with the long-distance advantage of fiber optics to provide high-performance extended connectivity for rack-mounted AI systems.
The speed of training AI models depends on "scale-out" and "scale-up."
"Scale-out" connects multiple computers via a network for collaborative computing, typically requiring long-distance transmission and primarily relying on fiber optics. "Scale-up," on the other hand, involves packing more GPUs into a supercomputer, allowing them to work collaboratively like a giant brain, primarily relying on copper cables for short-distance, high-density connections.
Point2's cable consists of eight e-Tube fibers, each capable of transmitting over 200 gigabits of data per second.
With Nvidia's plan to increase the number of GPUs per system from 72 to 576 by 2027, data transfer rates are soaring to terabit levels. At this point, copper cables encounter the physical limit of the "skin effect."
The skin effect refers to the phenomenon where, when alternating current flows through a conductor, the higher the frequency, the more the current tends to flow on the surface (skin) of the conductor, resulting in wasted space in the middle and increased resistance.
Faced with the physical bottlenecks of copper cables and the high cost of fiber optics, startups Point2 Technology and AttoTude have taken a different approach, utilizing radio wave technology to transmit data.
Point2 is about to mass-produce a polymer waveguide cable called "e-Tube," which incorporates a chip that converts electrical signals into millimeter-wave signals. Its 1.6 Tb/s version contains eight thin cores, with each waveguide utilizing both 90 GHz and 225 GHz frequency bands to carry data.
The pluggable modules at both ends of the cable can directly convert digital signals into modulated millimeter-wave radio frequency signals. A single cable can provide a total bandwidth of 1.6 Tb/s and a transmission distance of up to 7 meters, sufficient for rack-mounted expansion needs.
The e-Tube cable, transmitting 1.6 terabits per second, has a cross-sectional area only half that of a 32-gauge copper cable, yet its transmission distance is 20 times greater. (Image source: Point2) RF cables not only solve the distance problem but also achieve breakthroughs in energy efficiency and cost. Point2 data shows that its system power consumption and cost are only one-third that of optical transmission solutions, with latency as low as one-thousandth.
In contrast, while manufacturers like Credo have introduced active cables (AEC) with built-in "retimers" to extend copper cable life, this increases power consumption and complexity.
Another company, AttoTude, is also exploring similar concepts but targeting a higher frequency range. The system integrates a digital interface, a terahertz signal generator, and a mixer, enabling data encoding onto carrier waves ranging from 300 to 3000 GHz and transmission via a narrow dielectric waveguide.
The company has successfully demonstrated a transmission rate of 224 Gb/s at 970 GHz using a 4-meter-long waveguide, and anticipates a future feasible transmission distance of approximately 20 meters, showcasing the technology's potential for longer-distance applications.
AttoTude founder Dave Welch points out that photonics technology suffers from reliability issues such as "link oscillation" and requires extremely high manufacturing precision; while radio frequency (RF) technology, based on mature electronic manufacturing processes, offers higher reliability and does not require the micrometer-level alignment precision of optical fibers.
Although RF cables will initially appear in pluggable interface form, the ultimate goal of both companies is to integrate RF transceivers directly into the GPU package. Nvidia and Broadcom are currently attempting to co-package optical modules with processors (CPO), but face significant manufacturing and heat dissipation challenges.
Radio frequency (RF) solutions, due to their longer wavelengths, offer far greater tolerance for packaging alignment precision than fiber optics and significantly reduce heat dissipation requirements. With connector giants like Molex and Foxconn entering the market, this "radio waveguide" technology is expected to replace some copper cables and optical fibers in future AI data centers, becoming a new artery for computing power expansion.
