Page 89 - 2020 Interconnect Innovations eBook

Today, new fiber optic connector varieties that will shape the future of network equipment and data center networks are being introduced. The first subset of these new connectors is called smaller form factor, which still has the SFF acronym. A few more descriptive, though not necessarily standardized, identifiers exist under this new SFF category. The first is the FOCIS 19 connector, which gains its identity from the TIA 604-19 Fiber Optic Connectivity Intermateability Standard (FOCIS). FOCIS 19 connectors are also occasionally referred to as CS or SEN connectors and were developed to fit two duplex connectors in the QSFP-DD footprint, which wasn’t possible with LC duplex connectors. These duplex connectors have a unibody construction that employs the same 1.25mm ceramic ferrules proven in LC connectors. FOCIS connectors also share a similar look and feel and employ side-by-side ferrules like LC connectors, but they have a much smaller body and pitch. This smaller form factor was driven by the 2:1 breakout as originally defined in the QSFP-DD, OSFP MSA, and COBO specifications.
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» Connector size comparison within the QSFP-DD footprint: LC duplex (top) and FOCIS 19/CS/SEN (bottom). FOCIS 19/CS/SEN connectors provide twice the density as standard LC duplex connectors within the QSFP-DD footprint.
FOCIS 19 connectors are the ideal solution for 2:1 breakout transceiver applications. However, with the introduction of SFP-DD and additional 4:1 breakouts schemes in QSFP-DD, it became evident that yet another SFF connector would be needed. Although, this in no way obsoletes the need for the FOCIS 19 connector, which should continue to advance, and especially for the 2 x 100Gb/s, 2 x 200Gb/s, and 2 x 400Gb/s DCI applications.
These new SFF connectors are sometimes referred to as ultra-small form factor (USFF) or very-small form factor (VSFF) connectors. They introduce several innovative features and design approaches that not only increase density for use in 4:1 QSFP-DD and 2:1 SFP-DD applications but, also ease installation and maintenance and enable flexibility when cabling leaf and spine networks.
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