Fiber-optic polishing moves from the laboratory to the field

March 1, 1996
As optical fiber moves deeper into the network and becomes more popular as a medium for voice and data communications, both manufacturers and cabling contractors have come to recognize that field polishing is necessary. This increases the importance of fiber-optic polishing equipment, which can help the contractor do the job more efficiently while improving fiber performance.

Lynn Haber

As optical fiber moves deeper into the network and becomes more popular as a medium for voice and data communications, both manufacturers and cabling contractors have come to recognize that field polishing is necessary. This increases the importance of fiber-optic polishing equipment, which can help the contractor do the job more efficiently while improving fiber performance.

Manufacturers have made advances in polishing technology that have reduced the number of steps required and decreased the amount time it takes for polishing. They have also introduced power polishers that deliver increased precision and more-consistent performance.

There have been no breakthroughs in fiber-optic polishing technology during the last few generations of products, but contractors are satisfied with the incremental improvements manufacturers have made. In fact, with connector manufacturers selling product-specific polishing kits, contractors often get to choose the type of polishing they will do, based on which manufacturer`s products they use.

Recognizing that fiber-optic polishing is the most difficult part of the installation process, Sam Parthemer, project manager and engineer at Datalink Solutions Inc. (San Diego, CA), opts for light crimp-style connectors from Harrisburg, PA-based AMP Inc. "Polishing takes about 30 seconds per connector," he says. However, contractors must often work with several vendors` connectors because of customer requests. This means that Parthemer also uses AMP epoxy connectors and products from Siecor Corp.

Such freedom of choice can be a double-edged sword, however. Because polishing kits are vendor- and product-specific, contractors may have to buy several kits and have the associated consumables on hand. That is why many contractors would like to see standardization among product manufacturers. "I`d like to see a polishing tool that would have interchangeable dies for the different vendors` connectors," says Parthemer.

The cost of polishing kits is also of concern to contractors. Greg Clawson, vice president of Clawson Communications (Greenwood, IN), says that he adds $1 on to the price of each ST connector when he is bidding on a job. "If I buy a polishing kit for $250 to $300 that`s good for 500 connectors, that comes out to approximately $.50 or $.60 per connector," he says.

Looking at the cost of all job materials, Clawson points out that the cost of tools for fiber termination has not come down. "It seems outrageous to me that a plastic polishing puck costs almost $30," he adds.

Types of polishing

There are two types of fiber-optic polishing: that which is done in a factory (generally used for terminating multifiber cable) and that which is done in the field.

Equipment used in a factory setting is automated and consists of bench-type devices typically capable of handling 6 or 12 fibers. Several vendors make these bench-type polishing products, which may cost at least $10,000. In fact, according to Alan Woodman, product manager at Buehler Ltd. (Lake Bluff, IN), his company recently discontinued production of a 24-fiber polisher because it was costly, and cable-production houses preferred 6- or 12-fiber polishers.

During the past few years, Buehler has introduced two new bench-style products: the Fibrpol 2000 for eight connections, priced at $9850; and more recently, the Fibrpol 3000 for 12 connections, priced at $11,950.

According to manufacturers, in-house polishing equipment is adaptable to all major connector types, including ST, SC, FC, D4 and biconic devices. Mechanically controlled polishing gives 60 decibels or better return-loss performance, compared with 40-dB performance only three years ago.

Steve Baldo, national sales manager with the fiber optics group at Seiko Instruments USA Inc. (Torrance, CA), says that most machines can gang 6 to 12 connectors at a time and can do ultraphysical-contact, or ultra-PC, polishing in approximately 5 to 10 minutes. "Ultra-PC polishing requires a clean environment, and the equipment needs to be maintained, which is why it`s a difficult process to do in the field," Baldo adds.

Automated, bench-type polishers are used for the most part by cable-assembly houses and central-office equipment and distribution equipment manufacturers. Bench-type polishers are preferred for the singlemode fiber commonly found in long-haul and cable-TV applications. This is because polishing is more critical to performance compared with multimode fiber applications, such as interbuilding local area network connectivity.

According to Baldo, automated polishing machines have not changed significantly. What has changed in polishing is the materials, such as the abrasives. 3M Telecommunications System Division (Austin, TX), for example, has developed microabrasives and abrasive slurries that provide finer polishing finishes.

The cost of in-house polishing machines has recently decreased--from a range of $20,000 to $25,000 to a range of $15,000 to $20,000.

Polishing reliability

The polishing reliability achieved in the factory is difficult to match in the field because of external conditions, such as weather, dirt and polishing location, as well as inconsistencies introduced by user applications. However, because field polishing is necessary, it remains a market for connector manufacturers willing to improve on processes and products.

Field polishing is usually done manually, but power tools for this task are available from several manufacturers, including 3M and Buehler.

Handheld polishing kits include pucks, plates, lapping film, and other tools and accessories. Companies such as Automatic Tool and Connector Inc. (Union, NJ) make approximately 40 different polishing kits, which vary by connector type. Products also distinguish between multimode and singlemode fiber.

According to Dominick Tambone, international sales manager at Automatic Tool and Connector, kits of all kinds are in high demand among field contractors for data and network installations, telephone central-office locations and cable-TV headends, as well as for maintenance applications.

Epoxyless connectors

Field polishing is more common for multimode than for singlemode fiber. Fiber termination for data and local area network applications has always been done in the field, and, notes Tambone, the process has become quicker and easier. "Today, contractors can use epoxyless connectors that require no glue or heating ovens, and in two to five minutes, the fiber is polished, connected and installed," he says. This is in marked contrast to methods used only a few years ago, where termination procedures required the use of epoxy mixes and oven curing; typical connection time was 20 to 30 minutes.

Regardless of the procedure used, polishing objectives remain the same: a clean, scratchless polish on the glass endface of the optical fiber that permits the unobstructed passage of light.

Connector manufacturers report greater satisfaction with polishing technology among field contractors, many of whom agree that it has gotten easier and they don`t have to carry around as many items and tools. "Today, the contractors have a bag of connectors and are on their way," says Tambone. "The process has gotten much less cumbersome."

The main components needed for field polishing are a high-quality flat glass plate, lapping film and a polishing tool or puck. The polishing tool must provide a close fit for the connector to keep its ferrule from moving around during polishing. A loose fit can result in the ferrule not being perpendicular to the axis of the fiber. If the two fiber endfaces that are to be mated do not meet properly, it increases the transmission loss and can also cause scratching of the glass.

Another important consideration for field polishing is the use of clean lapping film and tools, which helps produce consistently high-quality polishing.

The quality attainable with field polishing is directly related to the quality of the connectors used. Both manufacturers and contractors say that there have been improvements in both procedures and components.

Frank Bucior, vice president of the construction division at Comstock Communications (Danbury, CT), is particularly pleased with AT&T`s ST II Plus easy connector. Using a diamond polishing paper, he can repolish the connector if the glass fiber breaks during termination; this avoids the expensive alternative of cutting off the connector and replacing it. "There have definitely been improvements made, and now there is greater flexibility in the polishing area," Bucior adds.

Telephony and cable TV

Field-polishing techniques for singlemode fiber used in data applications have remained consistent over the years. However, polishing for telephony and cable-TV applications, where exacting backreflection specifications are critical, is only recently coming into its own.

According to Automatic Tool and Connector`s Tambone, both new techniques and tools are available for contractors who are doing singlemode fiber terminations for these applications. For example, new diamond-lapping films can now be used with manual polishing tools. A soft surface is placed on the glass plate, and the diamond-lapping film sits on the soft surface. "This, used with a clean polishing lubricant, helps provide the best possible glass surface, one which is free of defects," says Tambone.

Furthermore, polishing tools or pucks that do not leave a residue on the expensive diamond lapping film are vital to the polishing process. Other tools required for singlemode fiber polishing include high-resolution microscopes for inspection and backreflection meters to test return loss.

When working with these more-expensive materials, industry experts say that cleanliness is critical. Polishing practices must include rinsing off the lapping film before use and when possible, avoiding working in dusty environments. Manufacturers and contractors agree that hand polishing relies on touch and feel; the process takes much practice if the technician is to achieve consistency of movement and regular application of pressure.

Training, then, is an important component of fiber-optic polishing, particularly in the field where attaining precision falls on the contractor. Manufacturers readily supply free training, and contractors applaud its availability. This training, however, is usually specific to individual manufacturers` polishing kits, which in turn, are specific to their connectors.

Most technicians in the industry believe that there is something different about every connector system, and so it pays to have someone demonstrate polishing on the different types of connectors. "It takes one to two hours to train someone, but without proper training, problems in the field could take much longer to figure out. Proper training alleviates termination procedures as a culprit," says Tambone. Procedures for terminating a connector and polishing it go hand in hand, he adds.

Terminating singlemode fiber in the field for telephony and cable-TV applications has only recently become a common practice. In fact, Automatic Tool and Connector reports 20% to 25% sales growth in this area over the last year. The company believes that what is driving the growth of terminating singlemode fiber in the field is the requirement for maintenance as the deployment of fiber grows. Singlemode field termination was considered to be an unacceptable practice only a few years ago.

Power tools

While the manufacturers that make automated polishing tools boast that they are more precise than manual polishing equipment, contractors report that such automated tools are not practical for field polishing. "I can`t use an automated polisher if I`m standing on a ladder in a small closet," says Clawson of Clawson Communications. Some contractors also prefer the flexibility of polishing manually.

However, under the proper circumstances, contractors agree that power polishers are useful, even if they are wary of the cost, which averages a few thousand dollars above that of manual polishing kits.

Buehler offers its Fibrmet single-station, portable polisher for $3470. Often used in small laboratory settings, it is also purchased by field contractors looking for improved consistency, better uniformity and higher quality in their polishing, according to Woodman. As users demand higher data rates, he notes that contractors will have to turn to power polishers for increased precision and higher performance.

Woodman concedes that the Buehler product, weighing 25 pounds, is not as portable as the company would like it to be. However, a lighter product means a performance tradeoff that Buehler has not been prepared to make. "We`ve shied away from a lighter design because it would mean a less-accurate, less-dependable product," he says.

The Fibrmet, according to Woodman, is a durable, heavy-duty product that does not require a water connection; rather, water can be applied using a vendor-supplied spray bottle. The automated polisher uses a 12-volt battery.

3M heeded the requests of field contractors to expedite the polishing process when it introduced its hot-melt connectors a few years ago. Hot-melt connectors require a one-step polishing process that uses the company`s 6850 polishing machine, which is priced at $995. The process takes less than a minute to complete using the 4-pound polisher, according to Dan Silver, sales and marketing manager of the 3M Telecommunications Systems Division. The polisher uses dry, single-film polishing technology and runs off a 12-volt direct-current battery.

Clawson is particularly impressed with 3M`s hot-melt connectors. "It`s a one-paper polishing setup that`s really nice because the epoxy is already in the ST connector," he says. This reduces the consumables to a single sheet of paper--no epoxy, primer or syringes.

Unless contractors move to crimp-style connectors, fiber-optic polishing will remain a fact of life. High-quality polishing kits and hands-on experience, then, will continue to produce the best polishing results when it comes to field terminating fiber-optic connectors.

Click here to enlarge image

This one-step polishing system from 3M features a dry, single film-polishing technology. Changing back and forth from wet to dry film is eliminated, and there is no mess. The 12-volt direct-current unit comes with a 110V alternating-current to 12V DC converter.

Lynn Haber is a freelance writer based in Norwell, MA.

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