Page 90 - 2020 Interconnect Innovations eBook

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» Connector size comparison within a QSFP-DD footprint. Historically, MPO and LC duplex connectors have been the primary options for QSFP. But connectors with side-by-side ferrules may not be compact enough to support emerging 4:1 breakouts in QSFP-DD or 2:1 breakouts in the smaller SFP-DD footprint. USFF/VSFF connectors are especially designed to support these densities and specific breakout topologies.
This increased density within standard transceiver envelopes is achieved by a few mechanical design innovations. The first alters the orientation of the duplex ferrules to a vertical or stacked layout, which differs from the historical side- by-side orientation. This allows for a narrower connector body and, as such, more connectors in the same horizontal space. In order to compensate for the allowable vertical real estate in the SFP-DD and QSFP-DD transceivers, the pitch between the two ferrules had to be reduced by about 50%. This narrower pitch enables both ferrules to be contained within a single connector body.
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» Connector size comparison within a standard LC duplex adapter footprint: LC duplex (top) and USFF/VSFF (bottom). In addition to the transceiver density, USFF/VSFF connectors provide the added benefit of increased density when used in other parts of the system. Vertical ferrule orientation and a narrow pitch allow three duplex USFF/VSFF connectors to fit into the same space as a single LC duplex within a patch panel or outlet.