400G optical module application

In the field of 400G optical modules, there are two kinds of optical modules competing for supremacy: OSFP and QSFP-DD.

400G optical module power consumption

Although the two form factors look very similar, the OSFP optical module is much larger in all three dimensions, resulting in a package that consumes more than three times the total volume of a QSFP-DD optical module. The QSFP-DD MSA defines 2 packages with a maximum length increase of 15mm, but all lengths are outside the cage socket so it does not affect the switch port density comparison. The idea behind OSFP's larger packages is twofold. One is to leave more internal space for electronic components, and the other is to provide an integrated heat dissipation solution. While some high-power transceiver types such as long-haul DWDM may require heat dissipation, the integrated design of OSFP places a burden on all interface types.

QSFP-DD optical modules are more flexible, leaving the choice of heat sink to the host device design. Devices designed for high-power optical modules can integrate additional heat sinks into the QSFP-DD chassis as needed. QSFP-DD optical modules are also more flexible in terms of backward compatibility. QSFP-DD optical modules are dimensionally aligned with QSFP optical modules and their edge connectors, allowing QSFP optical modules to support QSFP-DD optical module slots without adapters. At the very least, this allows vendors to upgrade existing 100G-class products to 400G without redesigning the front panel.

400G optical module application

Many in the industry are skeptical that these smaller, non-integrated heatsink QSFP-DD packages will be able to support high-power applications, such as long-haul DWDM with coherent detection, until significant integration enhancements are achieved. Power and size constraints make it a logical location. Regardless, at least as far as the MSA definition is concerned, both modules define power options to cover basically all 400G application classes.

At present, the shape of QSFP-DD optical module is the smallest 400G optical module in the industry, and each rack unit provides the highest port density.