CPO optical module copper cable connection

In Co-Packaged Optics (CPO), copper connections are used for short-distance links between ASICs and optical engines, enabling high-speed data transfer while minimizing power loss and latency.

Role of Copper in CPO

Copper connections in CPO modules serve as short electrical links between the ASIC (or other processing chips) and the optical engine, which contains photonic integrated circuits (PICs) and electronic integrated circuits (EICs) . These copper traces are typically very short—often just a few centimeters—because longer copper runs would introduce signal attenuation, crosstalk, and latency, limiting bandwidth and energy efficiency . By keeping the copper path minimal, CPO designs can maintain high data rates while reducing the need for digital signal processing (DSP) or retimers, which consume additional power .

Technical Considerations

1. Bandwidth and Signal Integrity: Copper links in CPO must support extremely high SerDes speeds (e.g., 112G to 224G per lane). Short copper traces reduce insertion loss and maintain signal integrity, which is critical for AI and HPC workloads .
2. Thermal Management: Co-locating high-power EICs and ASICs on the same interposer or substrate can generate significant heat. Copper connections must be designed to handle thermal expansion and avoid performance degradation .
3. Mechanical Integration: Copper attach formats are standardized in some CPO modules, such as the 3.2Tb/s Implementation Agreement, which defines electro-optical-mechanical specifications for copper and optical interfaces .
4. Distance Limitations: Copper is effective only for very short distances within the package. For longer interconnects, optical fibers are preferred due to lower loss and higher bandwidth density .

Advantages of Copper in CPO

• Low Latency: Short copper traces provide near-instantaneous electrical signaling between ASICs and optical engines.
• Cost and Reliability: Copper is cheaper and more robust than optical fibers for intra-package connections.
• Simplified Design: Reduces the need for complex DSPs or retimers, lowering power consumption per bit .

Deployment Context

In modern AI and HPC data centers, CPO modules often combine copper for short internal links and optical fibers for external high-bandwidth connections. This hybrid approach allows data centers to achieve high bandwidth density, energy efficiency, and scalability while overcoming the physical limitations of copper alone . In summary, copper connections in CPO optical modules are critical for short-range, high-speed electrical links that bridge ASICs and optical engines, complementing optical fibers for longer-distance data transmission and enabling efficient, high-performance data center architectures.