Achieving mass deployment of fibre in the LAN environment has been an elusive goal for the fibre industry for the past 10, or so, years. It has been plagued by high precision, costly and difficult to assemble components that are not very craft-friendly.
In developing this new technology, 3M has embraced the same attributes in the design that has allowed the current UTP (unshielded twisted pair) copper technology to be successful, including ease-of-use, quick termination and the general appearance and familiarity of a RJ45 connector.
Aspiring to make a fibre interconnect similar to a copper interconnect helped 3M to shift the development focus to one of significant change rather then mere enhancement. The resulting SG connector (known by its trade name as VF-45) has been adopted by the ANSI T11 (Fibre Channel) committee as the future small form factor connector for high-density applications. It also ensures simplicity of use and robustness in performance.
Current SC and ST fibre connectors employ precise ceramic ferrules and alignment sleeves to provide protection, guidance and a means to bring the fibre end surfaces together to create physical contact and optical continuity (Figure 1). This technology is inherently expensive because the precision needed for the ceramic parts is in the order of a few microns. Moreover, even though ferrules are produced in the millions, the basic high volume price has not shifted from more than US$1 (R6.20) a piece, thus ceramic parts alone in a duplex interconnect cost about US$6 (R37.20). In addition, field termination with epoxy-less connectors takes between five and ten minutes per connector, compared to about two minutes for a Category 5 UTP termination, which adds to the overall installation cost.
The VF-45 interconnect has been described in commercial literature as using injection moulded parts and relies on the fibre`s inherent precision to provide the required alignment. The V-groove provides a very convenient and simple structure where the precision geometry of the fibre can be utilised to enable physical contact and optical continuity as in a ferrule-based interconnect. This interconnect, however, is extended to a pluggable type connector and designed in such a way that the natural spring forces of the fibre are used to keep the fibres aligned in the V-groove as well as to maintain physical fibre-to-fibre end-face contact. The main tolerance to consider in this alignment scheme, other than the fibre`s basic tolerances, is the flatness of the V-groove. This is easier to control than concentricity of a ceramic ferrule, as the `V` shape is formed from a triangular piece in an injection moulding tool that is ground to the required flatness. The most precise injection moulded part used in this interconnect is held to within +75 microns which is a common injection moulding tolerance for small parts.
The VF-45 interconnect consists of a socket and a plug assembly, exactly like an RJ45 modular plug and jack as illustrated in Figure 2.
Threading a 125um +1um diameter optical fibre into a precision hole of less than 127um (max) diameter has been a difficult operation to automate when factory terminating ferrule-based connectors. There are no such threading operations required in this interconnect, therefore a fully automated termination process can be obtained.
Fibres in the plug reside inside a protective shroud and are suspended in free space. A front door cover ensures the fibres are not exposed, minimising contamination and user interference.
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