London, September 2005

Small Form Factor Connectors Ease Fibre Optic Integration

The small form factor (SFF) specification for connectors and interfaces has been available for a number of years and has more recently been adopted to incorporate fibre optic technology.

The SFF Committee is an ad hoc group set up in 1990 and was initially concerned with the mechanical footprint and interfaces of small hard disk drives being used for laptop computers and small mobile devices. It is a forum where manufacturers and customers can try to find a consensus of the design of compatible and multisourced products.

The successful adoption of the SFF format by fibre optics meant that the world-wide market for fibre optic based SFF connectors, cable assemblies and adapter would be over $600million in 2004. Much of this will be spent on the transceivers that take the data carried on fibre optic networks and prepare it for use in assemblies such as arrays of hard disk drives. Each transceiver has to be connected to the equipment and that is now nearly always via a connector (pluggable small form factor). The advantage of the SFF design is that it provides higher density and higher speed data transmission.

One manufacturing company that can provide a complete solution of Pluggable SFF products is Fujikura DDK, a member of the SFF Committee, which makes the connectors and EMI cage, and its parent company Fujikura, who manufacture the Transceivers.

The Fujikura DDK SFF connectors consist of a surface mount connector (SPT-RS020B-12) which is soldered on to a PCB in networking equipment. Around the connector is assembled a two part cage (SPT-R020-CL/CT) to suppress the effects of electromagnetic interference (EMI). In to this connector is plugged a transceiver (FLCH-SW-3201 – for example), which has an industry standard interface used by more than a dozen transceiver manufacturers.

These SFF assemblies are being increasingly used in Fibre Channel and Gigabit Ethernet designs for applications such as RAID (redundant array of inexpensive devices) systems for data storage. SFF allows OEMs to double the number of ports in a same size chassis in networking equipment when compared with the standard SC fibre optic connectors (they are the same size as the copper based RJ-45 modular plugs traditionally used in networking).

There are a number of designers and manufactures of RAID systems in Europe, and usually for every connector there has to be at least one transceiver. Some manufacturers building the hubs that connect to the RAID system, however, do not supply the transceivers, leaving for the users to decide which type of transceivers they use.

Transmission speeds of the transceivers started at 1Gbit and have risen to 2.5Gbit. The next real jump is to 10Gbit and that is now available in the form of the XFP series. This can be seen in the table below.

Fujikura DDK (Europe), with its Sales office based in Chessington, Surrey, are responsible for the design-in and sales of the Small Form Factor Pluggable connectors and cages throughout Europe, and, according to Andy Richardson who is Fujikura DDK’s Sales and Marketing Manager, are also increasingly getting involved in the supply and support of the transceivers. Initially the transceivers were directly soldered to PCBs but increasingly designs are making use of the SFF connector. This allows transceivers to be upgraded as technology improves and the connections are ‘hot swapped’ allowing transceivers to be added or removed without powering the system down. The two piece cage (SPT series) is made of copper alloy with tin-lead plate and provides EMI protection by stopping any spurious signals affecting the interface. The interface between the connector and the transceiver is fixed by specification.

A similar system is offered for the XFP series, with the piece parts being offered by DDK as a one stop shop. The complete list of piece parts can be seen in the drawings below. XFP has a slightly larger footprint and as previously mentioned, offers speeds up to 10GHz. DDK are one of the first manufacturers to offer all these component parts from one source. Samples and data, are now available upon request.

XFP Cage & Connector for 10 Gigabit Pluggable Module