How to use liquid cooling in optical modules

Liquid cooling in optical modules enhances thermal management, enabling high-speed, high-density, and energy-efficient operation in data centers and HPC environments.

Overview of Liquid Cooling in Optical Modules

Liquid cooling is increasingly applied to optical modules to address the thermal challenges of high-power, high-speed optical transceivers. As data center power densities rise due to AI, HPC, and 5G workloads, traditional air cooling becomes insufficient, especially for modules operating at 400G, 800G, and future 1.6T speeds . Liquid cooling uses fluids with high thermal conductivity to rapidly remove heat, maintaining stable performance and extending module lifespan .

Types of Liquid Cooling

1. Cold Plate Cooling (Indirect Liquid Cooling)
   • A metal cold plate with internal coolant channels contacts the optical module via a thermal interface material (TIM).
   • Heat is conducted from the module to the coolant, enabling rapid heat transfer while maintaining hot-pluggable serviceability .
   • Advantages: easier retrofitting, lower cost, compatible with existing infrastructure.
   • Limitations: only the top surface is cooled; side or bottom heat sources may remain less efficiently managed .
2. Immersion Cooling (Direct Liquid Cooling)
   • Entire optical modules or servers are submerged in dielectric, non-conductive fluids.
   • Heat is transferred directly to the coolant, eliminating hotspots and providing uniform cooling .
   • Can be single-phase (no phase change) or two-phase (phase-change cooling) depending on the fluid used .
   • Advantages: superior thermal performance, supports ultra-high-density deployments.
   • Limitations: higher cost and system complexity.
3. Silicon Photonics Integration with Liquid Cooling
   • Silicon photonics (SiPh) modules reduce power consumption and, when combined with liquid cooling, further improve energy efficiency by up to 30% .
   • Hermetically sealed, high thermal conductivity packaging ensures effective heat dissipation in liquid environments, supporting QSFP112, QSFP-DD, OSFP, and future 1.6T modules .

Applications in Co-Packaged Optics (CPO)

• In CPO systems, optical modules are integrated with switch chips on the same substrate, increasing power density and thermal crosstalk.
• Cold plate liquid cooling effectively maintains optical module temperatures (e.g., 31.3°C for modules in a 51.2 Tbit/s system) while keeping temperature differences minimal, ensuring reliability and signal integrity .
• Liquid cooling enables high-bandwidth, high-density interconnects without performance degradation due to overheating .

Benefits of Liquid-Cooled Optical Modules

• Enhanced Thermal Efficiency: Rapid heat removal prevents hotspots and maintains stable operation .
• Higher Power and Port Density: Supports high-speed modules in dense data center environments .
• Energy Efficiency: Reduces power usage effectiveness (PUE) and lowers overall energy consumption .
• Extended Module Lifespan: Lower operating temperatures reduce stress on components, improving reliability .
• Compatibility: Supports hot-plugging and integration with existing data center infrastructure .

Conclusion

Liquid cooling technology is critical for modern optical modules, particularly in high-performance, high-density, and energy-sensitive environments. By combining cold plate or immersion cooling with silicon photonics and co-packaged optics, data centers can achieve efficient thermal management, higher module speeds, and improved reliability, making liquid-cooled optical modules a key enabler for next-generation networking and computing systems .