Extending Copper Interconnects to 448G: Innovations Overcoming Conventional Limitations

Author: Andrew (Luxshare), with Jack Wang, Ming-Chung Wang, Jin-Wa Chen, Charles Grant Collection: 2025 OCP Global Summit - Expo Hall Sessions

Summary

Luxshare presents measured results demonstrating that 448 Gbps PAM4 over copper interconnects is achievable through improvements in three key areas: the CPC (Co-Packaged Copper) interface using Coolio elastomeric technology, front-panel IO using a new OSFP-like elastomeric connector, and twinax cable design. The company builds on its 2024 OCP demonstration of 224 Gbps CPC with Microsoft and MediaTek (45-46 dB channel loss, BER 10^-7 with FEC tails <5) to show measured bandwidth extension past 110 GHz -- the Nyquist frequency for 448G PAM4.

The CPC improvements were developed in two phases. Phase 1 addressed test board and elastomer optimization alone, extending clean response to ~80 GHz with improvement visible to 100 GHz. Phase 2 added shrunk Coolio connector geometries to suppress higher-order mode excitation, achieving clean, flat insertion loss response past 110 GHz in measured (not simulated) data. The front-panel OSFP challenge is that current 224G OSFP connectors suffer from stub effects at the mating interface above 56 GHz Nyquist. Luxshare is exploring elastomeric front-panel interfaces in an OSFP-like form factor (same approximate lane/port density but not backwards compatible) to eliminate stub-induced resonances. Twinax redesign from 224G to 448G eliminated resonances above 60-70 GHz, achieving clean ILD past 110 GHz in first-revision measured results.

Andy Bechtolsheim showed results at OCP from a collaboration with Luxshare, Altera, and Mike Lee demonstrating 448G PAM4 working with Luxshare's measured channel models. A major silicon SerDes vendor is also evaluating PAM4, PAM6, and PAM8 with Luxshare's technology, with PAM4 looking viable. The 448G CPC measurement is on display at Luxshare booth B21.