History has been very clear that for broad industry adoption of the 800G generation, an optical pluggable form factor must be judged on:
(1) Backwards compatibility with previous generation optics
(2) 100G+ electrical performance
(3) Excellent thermal power dissipation

The recent QSFP-DD MSA updates ensure all of these, but I'd like to focus on the thermal performance here. Starting with 400G modules and continuing with 800G pluggable modules, the challenge of thermals and keeping optical pluggable modules cool has be front of mind for many.

Let's be clear, no one wants optical modules to consume high power, and the vast majority of modules deployed today operate well below these maximums we design to for the system.

However, from a system designer perspective, it is important to know what the maximum a system can deal with while maintaining the module's optimal operating performance. And from a network operator's perspective, it is important to know that the module type can support all the different reach options you want to deploy.

With 400G, we saw the coherent optical modules fitting into the QSFP-DD form factor which provided network operators with maximum flexibility with the systems they deploy which could truly be flexible in supporting copper cables through to coherent optics from the same port. This ability is accelerating the exciting new Cisco Routed Optical Networking solution.
With the rise of 800G modules, the QSFP-DD MSA took the opportunity to enhance both the electrical and thermal capabilities to be ready for all variants of modules. The updated D6.0 specifications were just released which includes the QSFP-DD800 and QSFP112 module definitions. The MSA also published an informative thermal whitepaper showcasing the flexibility that the QSFP module family has when it comes to thermal designs. The fixed heatsink on the nose of the module outside the faceplate, combined with a flat-top module inside the cage enables optimized heatsink designs that can provide excellent thermal performance while minimizing airflow impedance (which means you can run the fans slower and save more power).

For OFC 2021, we thought we'd showcase what all of this means with a simple QSFP-DD800 thermal demo. Using a prototype system capable of supporting 32 ports of QSFP-DD800 in a 1RU system, we installed 32 thermal load modules from MultiLane all set for 30W each.

The key parameters we worry about with a system's ability to cool a pluggable module is the case temperature and the temperature rise compared to the ambient temperature.

With all 32 thermal modules set to their maximum setting of 30W, the fixed 1RU system was able to easily handle keeping them cool. An average temperature rise of ~ 30