High-speed copper cable connection replaces optical module

High-speed copper cables, such as DACs, are increasingly used for short-distance connections in data centers, offering cost, energy, and latency advantages over optical modules.

Overview of High-Speed Copper Cables

High-speed copper cables, often referred to as Direct Attach Copper (DAC) cables, are designed for short-distance connections, typically within a single rack or between adjacent racks . Unlike optical modules, DAC cables have fixed connectors at both ends and do not require separate transceivers, making them a low-cost, high-efficiency solution for high-speed data transmission . They are widely adopted in AI server racks, such as Nvidia's GB200 deployments, where short-range, high-bandwidth connections are critical .

Advantages of Copper over Optical Modules

1. Low Latency and High Reliability: Copper cables provide near-zero latency and stable performance for short distances, which is essential for high-power AI clusters .
2. Energy Efficiency: Passive copper cables do not require external power, and even active copper cables consume minimal power (~440 mW), reducing overall energy demand .
3. Cost-Effectiveness: Copper cables are significantly cheaper than fiber optics, lowering the cabling cost for entire data centers .
4. Thermal Management: In high-density racks (up to 120 kW), copper avoids the heat issues associated with electro-optical conversion in optical modules, simplifying cooling requirements .

Limitations and Use Cases

While copper excels in short-range connections (under 2 meters), it faces signal attenuation and crosstalk over longer distances, making optical modules preferable for inter-rack or campus-scale links . Optical cables, such as Active Optical Cables (AOCs), support kilometer-scale distances and higher bandwidths (up to 1.6 Tbps), but they are more complex, power-hungry, and expensive due to the need for optical transceivers and DSP electronics .

Industry Perspective

Nvidia CEO Jensen Huang emphasized that copper cables remain indispensable inside AI server racks due to their zero power consumption, low latency, and high reliability, while optical modules dominate long-distance interconnects . This reflects a dual-era approach where copper and optical technologies coexist, with copper handling in-rack connections and optics managing longer links.

Emerging Alternatives

Beyond traditional copper and optical solutions, new interconnect technologies like e-Tube RF over plastic dielectric are being developed to combine the advantages of both, offering longer reach, lower latency, and energy efficiency for next-generation AI clusters . These innovations aim to overcome the limitations of both copper and optical cables while remaining cost-effective for large-scale deployments.

Conclusion

High-speed copper cables are not being fully replaced by optical modules; instead, they are optimized for short-distance, high-bandwidth, and energy-efficient connections within racks. Optical modules remain essential for long-distance links, while emerging technologies may further enhance data center interconnects in the future .