Getting in the V-Groove boosts information flow

Austin, TX--"Simplicate and add lightness," so goes the old British aerospace saw. Mix in the modern design mantra of "cut cost" and you have the charge 3M's Telecom System Division designers took to heart in perfecting its patented VF-45^TM Volition^TM high-speed fiber-optic interconnect.

The quest for ever increasing data-communications bandwidth, whether for engineering information or office communications, is a forgone axiom of modern technology. What's also a given is the torrent of digital information that can be carried by laser light through optical-fiber networks. The only hitch in the process is the high cost of installing fiber to the desk for computers and workstations throughout an enterprise. Slower copper connections are still economically justified by their low-cost installation. Fibers, with diameters measured in hundreds of microns, require precision cutting, polishing, and alignment by field personnel--eating up valuable time and obviating the fiber data stream advantage.

Time is money. Conventional fiber-optic connectors rely on precisely-made cylindrical ceramic "ferrules" to hold, align, and protect the slender fibers. Fiber ends must be polished to tight tolerances to mate fibers for maximum light coupling. And the fibers must be aligned and glued within the ferrule. Thus the cost of field terminations is driven by fiber polishing and epoxy cure times of several minutes.

3M's Volition concept relies on simple molded plastic parts forming mating sockets and plugs, similar in concept to the ubiquitous RJ-45 phone jack. Only 11 molded components make up a duplex connection--as opposed to about 40 parts previously (see figure).

Right-angle V-grooves in the VF-45 sockets align mating fibers from the plugs using the inherent precision of the fiber diameters (see DN 6/8/98, p. 76). Fiber flexing, and a leaf spring cradling the fibers inside the plug, supply fiber end face mating force and connection integrity.

Inspiration for the VF-45 design came from Jim Bylander, technical manager for the 3M Optical System Laboratory. He notes the company took a fresh look at the fiber-optic connection market in 1992. The conclusion: the whole plug/coupling/plug ferrule-type architecture would have to change to foster widespread fiber use. "And you couldn't just change the fiber and connector aspect, but the whole system," says Bylander, including the equipment such as transceivers in hub locations.

Simple phone-jack style architecture would foster efficiencies network-wide. Stronger glass fibers were also becoming available, which aided in "signal integrity and craft worker productivity," Bylander adds. "Data transmission distances possible with glass fiber allow a 'collapsed backbone' eliminating many utility closets, which now put all equipment in central locations." And in these hubs electronics can be optimized for a complete enterprise rather than a smaller cluster of clients.

Just browsing, thanks. As for the Volition configuration, Bylander says this came from a trip to that design-idea cornucopia--the local hardware store. Here he had picked up a common molded plastic "mud plate" for a telephone wall box installation. Looking at the surface angles and finish on the plate led him to a conclusion: commercial molding methods and tolerances could allow low-cost production of connector parts precise enough for fiber-optic connections. 3M had used V-grooved alignment previously and molding such grooves for fibers might be the key to a cost-efficient connection scheme.

A 3M marketing manager who heard of Bylander's idea helped further company interest. A design team was assembled in Austin to bring the concept to maturity. Issues included: static fatigue of the bowed fibers within the connector; proper angling of the fiber tips to insure snag-free travel along the V-groove (a 35° circumferential bevel); and fiber coating (a proprietary silicon epoxy for strength and sliding). Fiber retention using ultrasonic and microwave welding was considered, along with adhesives and clamping. To secure socket fibers, a mechanical grip was chosen. For the plug-tipped patch cords, a light-cured adhesive is used during manufacture. In addition, companies involved in fiber optics and copper cabling were solicited for datacom service and experience.

3M Senior Product Development Specialist and design-team leader Sid Berglund notes a vital link was the manufacturing site set up across the hall from the development lab by Manufacturing Technology Engineering Supervisor Jay Borer.

Here tools such as stereo-lithography rapid prototyping allowed models to be made in a day or two. Electronic files for promising designs allowed mold makers to fabricate tooling and assess a design's manufacturability, mold wear, parts assembly, and performance. Such tooling technology was key for downstream time savings and ease of use in installation.

Precision built into the mold geometry and surface finish permits low-cost molding of plastic parts for V-groove fiber alignment in the wall sockets during field assembly. On the other hand, the plug-tipped standard jumpers of from 1 to 30 m, connecting the fiber sockets with end-user systems, are manufactured in-house. Thus, the fiber end beveling and polishing needed for the plug fibers to align and mate effectively can be carefully controlled.

Volition beta testing has encompassed industrial, financial services, and academic sites. These installations include running fiber cables around equipment and into wall boxes mounted on cinder blocks in dusty and vibration-prone environments while maintaining communications integrity. At George Washington University (Washington, DC), Volition was used for re-cabling the datacom network--resulting in 180 utility closets (with separate support costs) being reduced to 11 hub sites.

An alliance of electronics manufacturers and networking hardware vendors has formed the VF-45 Action Group to increase market acceptance and foster product design and development. The group also educates OEM and end users on the benefits of fiber optics in premises networks. Members include Siemens Microelectronics, Honeywell MicroSwitch, Corning, as well as 3M. Future developments will move the technology to outdoor applications and from dual to multiple fiber connections.

Additional details...3M, Telecom Systems Div., 6801 River Place Blvd., Austin, TX 78726, (800) 695-0447, e-mail: volition@3M.com

Jim Bylander, with more than 25 years at 3M, serves as technical manager for the Telecom Systems Division's Optical Systems Laboratory. His focus throughout his career has been telecommunications networks (including central-office switching, local-area networks, and transmission systems), connectors, splices, and splice cases.

For the past 10 years, Bylander has concentrated on the development of optical-fiber components, connectors and splices. He is currently managing the Optical Systems Laboratory in the development of specialty optical fibers and fiber Bragg gratings. He holds five patents in the areas of optical-communication components and cabling.

Prior to joining 3M, Bylander was at Bell Laboratories. He holds a bachelor's degree in mechanical engineering from the University of Wisconsin and master's degree from Purdue University.