Comparison of QSFP-DD with other types of optical modules

400G QSFP-DD optical module detailed introduction

The QSFP-DD (Quad Small Form Factor Pluggable-Double Density) Dual Density Quad Small Form Factor Pluggable is a package of high speed pluggable module defined by the QSFP-DD MSA group. It serves as the preferred 400G optical module package, enabling data centers to efficiently grow and scale cloud capacity as needed.

Features

It is forward and backward compatible with QSFP, and compatible with existing QSFP28 optical modules, AOC/DAC, and other compatible devices.

The QSFP-DD can achieve up to 14.4Tb/s of aggregated bandwidth in a single switch slot. It Features 8-channel electrical interfaces with rates of up to 25Gb/s (NRZ modulation) or 50Gb/s (PAM4 modulation) per channel, providing solutions for up to 200Gb/s or 400Gb/s aggregation.

By Using SMT (Surface-Mount Technology) connectors and 1xN cages, along with cage design optimization and module housing optimization, each module can achieve at least 12 watts of thermal capacity.

The transmission media include passive copper cable (DAC), multi-mode fiber (MMF) and single-mode fiber (SMF).

QSFP-DD vs. QSFP (QSFP+/QSFP28)

Bandwidth

QSFP-DD offers up to ten times the bandwidth of QSFP+ or four times the bandwidth of QSFP28.

QSFP has four electrical lanes at 10Gb/s (QSFP+) or 25Gb/s (QSFP28) per lane, aggregated to provide 40Gb/s or 100Gb/s solutions.

The electrical interface of the QSFP-DD pluggable package features eight channels at rates up to 25Gb/s (NRZ modulation) or 50Gb/s (PAM4 modulation) per channel, aggregating to provide solutions of up to 200Gb/s or 400Gb/s.

Compatibility

QSFP-DD is backward compatible with QSFP+/QSFP28. Systems designed with QSFP-DD modules are backward compatible, supporting existing QSFP+/QSFP28 modules and providing flexibility for end users and system designers.

Port Density

The QSFP-DD and QSFP+/QSFP28 systems have the same port density. However, because each QSFP-DD port can accommodate eight channels instead of four, QSFP-DD doubles the number of ASIC ports it supports for existing interfaces such as CAUI-4.

The mechanical interface of the QSFP-DD on the motherboard is slightly deeper than the QSFP+/QSFP28 to accommodate an additional row of contacts.

QSFP-DD increases the bandwidth to 10x/4x of QSFP+/QSFP28 with only a slight increase in length while maintaining the same port density, and is also backward compatible, which means customers can directly deploy QSFP-DD systems without using QSFP, thereby reducing a significant amount of equipment costs.

QSFP-DD vs. OSFP

OSFP is a new pluggable package with 8 high-speed electrical channels that will initially support a transmission rate of 400Gb/s (8x50G).

QSFP-DD and OSFP are both optical transceiver form factors designed for 400G and 800G high-speed interconnects. QSFP-DD achieves higher bandwidth through a double-density electrical interface while maintaining backward compatibility with QSFP28 and QSFP56, making it well suited for data centers that require smooth upgrades and high port density.

OSFP features a slightly larger form factor with superior thermal performance, making it more suitable for higher-power 800G optical modules; however, it does not offer backward compatibility and is typically deployed in newly built hyperscale or AI-focused data centers.

QSFP-DD prioritizes port density and backward compatibility, while OSFP excels in thermal performance and high-power 800G deployments—especially in next-generation AI data centers.