Connectors evolve for the premises market
A new generation of small-form connectors has arrived to bring fiber closer to the desk.
Joyce P. Kilmer optotec S.p.A.
The technology of fiber-optic connectors in the early 1990s seemed to have stabilized. After the acknowledgement of the death of the biconic connector (the so-called connector of the `80s), ferrule-based connector designs became the workhorses of the `90s. These designs converged into a group of three single-fiber connector types--the FC, SC, and ST. Standards groups such as the Telecommunications Industry Association (tia) and the International Electrotechnical Commission (iec) were putting the finishing touches on the FC, SC, and ST specifications and standards.
Behind the scenes, however, the stage was being set for new connectors that would vie to become the connector design for the new millenium. A convenient way to track this evolution of fiber-optic connectors is by following the activities of tia fo-6.3.4, the Working Group on Fiber Optic Connector Intermateability Standards, which writes the Fiber Optic Connector Intermateability Standards (focis) documents.
Not surprisingly, the first focis document, focis 1, covered the biconic connector (see table on page 42). The document is still available from the tia for users and manufacturers who wish to ensure that the biconic connectors they intend to use or manufacture will work with the embedded base of biconic connectors.
The next focis documents--focis 2, 3, and 4--cover the ST, SC, and FC connectors, respectively. The work on these documents is completed, and versions of them have been published recently. The only work still being done on any of these focis documents is on focis 4. Work is under way to create Revision A of focis 4--focis 4A--which will include specifications to address angled FC connectors. The plan is that once the angled connector issues are resolved for the FC connector, the group will begin addressing angled connector specifications for the SC connector. These specifications will then be incorporated into focis 3 and released as focis 3A. No work is planned to incorporate angled connector specifications into the ST (focis 2 document).
focis 5 is the first of the focis specifications to address a multifiber connector. focis 5 covers the basic USConec (Hickory, NC) MT element, which can handle 4, 8, 10, or 12 fibers. The element is packaged in a convenient push/pull connector body and is commonly known as the mtp/mpo connector. Work on focis 5 has been progressing and a draft is being balloted.
A new generation
The current excitement surrounding the new generation of connectors began in tia fo-6.3.4 in late 1996, with a simple request for new business to tia fo-6.3, the Subcommittee on Fiber-Optic Interconnecting Devices and Passive Products, which is the parent subcommittee to FO-6.3.4. The request, presented by Panduit Corp. (Tinley Park, IL), was simply to begin work on a new style of fiber-optic connector that would fit into an RJ-45 type jack. The request, which came from an ATM Forum technical committee, was for the standardization of connectors for plastic optical fiber for residential broadband applications. Panduit`s solution, the Fiber-Jack (FJ) connector, is a duplex connector that comprises two standard 2.5-mm outer-diameter ferrules configured together in a single RJ-45 type plug housing (see Fig. 1). The proposal for new business was approved and work was initiated for the FJ connector, which is now being marketed as the opti-jack, to become focis 6.
The approval of focis 6 sparked a flurry of activity from other manufacturers to bring their ideas for new connector styles and designs out from their research laboratories and before the fiber-optic standards bodies. The forum to present new connector styles and designs is tia fo-6.3.4--and the race was on for manufacturers to secure a focis number for their new connectors.
The members of this new generation of connectors have a few things in common:
They are targeted primarily for the
premises/residential market (at least initially).
They all have at least duplex (2-fiber)
capability.
They generally fit into an RJ-45 type
8-pin modular jack template.
The next to get its connector into the focis approval process was 3M Telecom Systems Div. (Austin, TX). focis 7 covers the generic SG connector (originally called the Galaxy connector) that is marketed by 3M under the brand name VF-45 (see Fig. 2). 3M claims that this new connector greatly reduces the time and cost of field terminations "by avoiding the use of ferrules and a large number of parts" (see Lightwave, July 1997, page 34, where the VF-45 was referred to as the VG-45, its name at the time of that writing--Ed.). The fact that no ferrules are used in this connector makes this distinctly different from the other focis connectors.
With great improvements being made today in the control of optical fiber`s geometrical parameters, ferruleless connectors are expected to become more common in the future. It is interesting to note that Bell Communications Research has written a new generic requirements document, GR-2919--"Generic Requirements for Hybrid Optical Splice Connectors for Single-Mode Optical Fiber"--which, unlike GR-326--"Generic Requirements for Single-Mode Optical Connectors and Jumper Assemblies"--addresses any ferruleless connector, as well as any connector/splice combination type connector.
Siecor Corp. (Hickory, NC) was the next to secure a focis document number. focis 8 covers the Mini-MT (or Mini-mpo). The Mini-MT is functionally the same as the MT (see Fig. 3). However, the ferrule is smaller, as it is designed to hold only up to 4 fibers (rather than up to 12 like the mtp/mpo).
focis 9 covers a multifiber connector introduced by Berg Electronics (Whippany, NJ). The Mini-mac is a multifiber connector capable of handling 2 to 18 fibers (see Fig. 4).
The most recent focis number officially issued, focis 10, was obtained by Lucent Technologies (Norcross, GA) for its LC connector, marketed as the Optispeed. The LC is different because it is based on 1.25-mm outer-diameter ferrules (half that of the 2.5-mm outer-diameter ferrules commonly used in the ST, FC, and SC connectors) to achieve a greater connector density in a frame (see Fig. 5). Also, the LC has a feature whereby the duplex connector can be separated into two simplex (single-fiber) connectors.
However, there are even more connector designs waiting for standards project approval in the focis document set. Expected to be focis 11 is Siecor`s new scdc/scqc, which uses a special ferrule to fit either 2 fibers--duplex (DC)--or 4 fibers--quadraplex (QC)--within an SC plug body (see Fig. 6). Also recently introduced is the mt-rj (expected to be focis 12), which is being jointly marketed by amp, Siecor, Hewlett-Packard, USConec, and Fujikura. This connector uses the same Mini-MT element as described in focis 8. However, it also employs the popular RJ type latching mechanism (see Fig. 7).
All of this focis activity is summarized in the table.
Looking ahead
Which of these connector types will prevail in the next millenium? Only time will tell. However, some interesting developments--and alliances--are occurring with the intent of promoting the broader acceptance of certain connector types.
One approach is to have a connector pre-recognized by a user group. For example, the ATM Forum has requested specifications for Panduit`s FJ connector. 3M`s new connector was adopted by the Fibre Channel Association asc-x3t11 Technical Committee. Also, IBM has stated that it is committed to the development of the scdc/scqc connector technology recently proposed by Siecor.
Another approach is to broadly license the new connector technology in order to get other manufacturers on board and build up a user base alliance. This is the approach that Lucent is employing with its LC connector. For example, Molex Fiber Optics recently announced that it had licensed the LC connector technology from Lucent.
One of the strongest user group endorsements for a new connector type would come from the tia`s TR-41.8 Technical Subcommittee, which writes the eia/tia-568 Commercial Building Telecommunications Cabling Standard. However, at a recent meeting of TR-41.8 the committee determined that it would leave eia/tia-568 with an "open, performance-based standard." Consequently, members decided against approving any single new connector design. Rather, they agreed to let the marketplace decide which connector type shall prevail (see "tia lets the connector market decide" on page 44).
So the ball is firmly in the court of customers to decide which connector designs they prefer. This must occur, because we had one connector type for the `80s, three connector types for the `90s, and now at least eight new types for the next decade! Thus, we seem to have diverging rather than converging fiber-optic connector standards, which, of course, is contrary to where standardization is supposed to take us. u
Acknowledgment
Special thanks are given to W. W. Wood, chairman of tia fo-6.3.4, for his input toward writing this paper.
Joyce P. Kilmer, Ph.D., is North American agent for optotec S.p.A. (New York, NY). He is also a member of Lightwave`s Editorial Advisory Board. He can be reached at http://members.aol.com/jkilmerphd/jpkhome.html.