Direct-to-Plug Liquid Cooling For Pluggable Optical Modules

Author: Bessad Mahajajer, Thermal Engineer, Ciena Collection: 2025 OCP Global Summit - Expo Hall Sessions

Summary

Ciena presents a direct-to-plug (D2P) liquid cooling solution for OSFP pluggable optical modules that integrates a cold plate directly into the module body, eliminating the dry sliding thermal interface that limits both riding heat sink (air) and riding cold plate (liquid) approaches. The standard OSFP integrated heat sink is replaced with a 5mm cold plate of identical thickness, assembled with miniature blind-mate quick disconnects (mini QDs) that mate automatically when the module is inserted into the host card. At 30C coolant temperature, D2P can cool up to 100W versus 55W for riding cold plates and ~35W for air cooling; at 45C warm water, D2P handles 70+W versus only 45W for riding cold plates.

The mini QD has a 5mm outer diameter (matching the cold plate thickness), tolerates 0.5mm misalignment, supports 0.1-0.2 LPM flow rates (0.9 LPM max), operates at 150 psi max pressure, and is rated for 1,500 mating cycles (versus 50-100 for the electrical connector). Developed in partnership with Staubli, the QDs are embedded in the manifold with retaining plates. The solution achieves minimum OSFP pitch with ganged cages: 32 ports per 1U (four 1x4 cages) or 36 ports per 1U (three 1x6 cages) in a 19-inch rack. Ciena has proposed adding OSFP D2P as a variant to the OSFP MSA for next-generation 3.2T plugs and plans a multi-vendor OCP contribution for the mini QD specification (confirmed contributors: Ciena and Staubli, plus two pending).