New connection technology simplifies installation and reduces cost
By avoiding the use of ferrules and a large number of parts, a new connector design may make fiber more economical for local area network and premises wiring applications
DAEN WOMBWELL
3m telecom systems div.
Although fiber outperforms copper for high-speed data transfer, particularly over long distances, the cost of components, electronics, and installation has impeded the widespread implementation of fiber-to-the-desk. In a recent survey, 92% of company representatives indicated that if cost were no longer an issue and fiber were competitive with copper in the horizontal loop, they would either change to fiber without reservation (50%), or seriously consider changing (42%).
One of the significant cost factors in transitioning to fiber in the horizontal loop is the number of connections required to link every workstation to the network. The unit cost of the connectors plus the installation expense can be prohibitive. A new fiber-optic duplex connector, recently named the VG-45, promises to reduce these costs dramatically. Its plug-and-socket configuration uses a simple mechanical connection that completely eliminates ferrules. This design provides a sevenfold savings in unit cost over the price of standard SC connectors and re quires an average termination time of only two minutes per socket (two fibers) with a yield of 98% or greater. The savings in labor alone are expected to be almost twice the value of the connector per unit installed.
The VG-45 connector consists of a few basic parts made from injection-molded, standard engineering plastic. It has the same footprint density and familiarity as the 8-pin modular jack. There are no adhesives required for installation, and the process is so simple that a trained fiber-optic technician, an electrical contractor, or an information technology support staff member could install and maintain the connector with the same level of signal integrity.
The plug-and-socket design provides a duplex connection that is approximately half the size of the standard duplex SC interface, thus allowing higher-density installations. For example, 24 of these connectors can be plugged across the typical width of a rack, compared to only 12 of the standard SC circuits (with 4 ferrules and 2 sleeves), depending on the patching scheme.
The connector is tested to iso 11801 and tia/eia-568a standards and the corresponding component standards (iso/iec, tia/eia). In addition, the VG-45 was adopted by the Fibre Channel Association asc-X3T11 Technical Committee in February 1997 as the new, small form factor interface for future variants of Fibre Channel.
Operational principles
The simplicity of the connector`s plug-and-socket configuration is demonstrated by the few number of parts required. While a standard duplex SC connector typically has more than 40 parts, 6 of which are high-precision, the new ferrule-less socket has only 3. These include a fiber holder that secures two or more fibers in place; a shroud and boot that protect the fibers and secure the cable to the connector; and an integral hinged door that acts as a dust cover, improving the durability of the connector in the field.
Socket construction includes a fiber holder that secures the fibers and simplifies termination; a main body that houses the special V-grooves that ensure exact fiber alignment and features an integral door to provide dust protection; and a housing base that snaps into place to complete the protective shell.
The interconnect between the plug and socket is simple (see Fig. 1). As the plug is introduced into the socket, the dust cover mechanisms of both the plug and socket engage automatically. The socket dust cover moves up while the plug cover slides to the side. The plug enters the socket, and the fibers within the plug travel along the V-grooves of the socket. The plug features a clip that locks with an audible "click" when fully inserted into the socket, ensuring signal integrity. As the plug snaps into place, the plug fibers bow, creating forward and downward pressure to optimize fiber-to-fiber optical contact.
The interconnect uses the precision of the optical fiber to obtain accurate core-to-core alignment as the fibers connect in the V-grooves. The V-grooves force the fiber to self-adjust for precision alignment. In addition, each fiber is allowed to adjust for variations in fiber lengths and changes due to environmental factors. Unlike the multiple fibers in a ferrule, the plug fibers are free-moving and, on mating, can self-adjust independently to achieve optimal performance.
Field termination
If migration to the desk is to be successful, then components must be simple to install, terminate, and maintain. Fiber termination with ferruled connectors is more complex and time-consuming than termination of copper and requires skilled technicians at high hourly rates.
With the new ferrule-less connector technology, the socket can be field- terminated in about 2 minutes, which saves time and labor costs over the 15-minute installation required for two standard SC connectors and an adapter (which are comparable to one of the new connector). An innovative duplex fiber preparation method speeds the termination process. The mechanical gripping action of the connector means there are no adhesives and, therefore, no curing time required; and, because there are no ferrules, fiber alignment is simpler.
As with the connector itself, the tooling has been designed to be inexpensive and easy to use. Only a few simple tools are required, reducing tooling costs to one-half to one-quarter of what they are today. A small, belt-mountable termination kit contains all the necessary tools.
The termination steps are as follows (see Fig. 2):
The socket fiber holder is placed into a puck. After the fibers have been stripped and cleaned, they are inserted into a socket fiber holder. When the puck is closed, it activates a clamping mechanism to securely lock the fibers into place.
As the puck is lifted and slid through the preparation station, the fibers are scored, broken, and polished. The tool has been designed to control the fiber break to precise tolerances while eliminating the need for skilled operators. After the fibers are cleaned and inspected, the socket fiber holder is snapped into the socket body, and the base is attached, completing assembly.
The socket is now ready to be installed into a patch panel or wall outlet. Once the connector is installed, a simple process allows quick on-site testing, which reduces testing time and the number of technicians required.
The VG-45 connection system requires minimal, if any, maintenance. The dust covers on both the plug and socket help prevent contamination so that the interconnect is extremely stable, even when exposed to hundreds of matings without cleaning.
When cleaning is required, a front-entry cleaning process that does not require the disassembly of sockets or wall outlets (as is currently required in ferruled connector systems) simplifies the procedure. The cleaning system consists of an office cleaning solution that is an environmentally safe, inert, nonflammable, nonconductive liquid; a spray container with nozzle; and a plug adapter.
The profile of the nozzle discharge head mates with the socket, allowing easy insertion. Once the head is inserted, the spray trigger is pulled and the container fires two high-pressure jets that clean the socket and plug fibers thoroughly. The cleaning solution evaporates in 5 to 10 seconds, leaving no residue on the fiber or the socket V-grooves.
Demand for high bandwidth
Emerging trends in information systems will accelerate user demand for high bandwidth. Rapidly growing networks streaming audio and video, desktop videoconferencing, and real-time decision support systems are some of the applications fueling the need for increased speed and bandwidth. Fiber-optic cabling will not only provide better performance for today`s 100-Mbit/sec networks but will continue to provide high performance for tomorrow`s gigabit speeds and high-bandwidth applications.
However, for fiber-to-the-desk to become common in the workplace, the costs of installing fiber networks must be dramatically reduced. This kind of reduction requires more than just an evolution in technology. Improvements of 10% (which is what some of the newer options offer today) are not sufficient to make the widespread use of fiber feasible.
The ferrule-less VG-45 connector is currently in field trials and is expected to be globally commercialized by the first quarter of 1998. It promises to provide the revolutionary improvement in connector cost and ease of installation, both of which are required to realize universal fiber-to-the-desk implementation. u
Daen Wombwell is program manager, fiber-to-the-desk, at 3M Telecom Systems Div. in Austin, TX.