Optical-fiber alternatives to premises solutions

Three years ago, the shortage of fluorinated ethylene propylene (FEP) used to insulate conductors in unshielded twisted-pair (UTP) cables caused problems throughout the premises cabling industry

Dec 1st, 2000
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Tony Beam, Tyco Electronics

Three years ago, the shortage of fluorinated ethylene propylene (FEP) used to insulate conductors in unshielded twisted-pair (UTP) cables caused problems throughout the premises cabling industry. Because of this shortage, cable manufacturers used alternate methods to satisfy the industry's requirements. Now the boom in the optical-fiber industry, combined with other demands, is causing not only cable manufacturers but also connector and cable-assembly manufacturers to again examine alternate but acceptable solutions for the premises cabling industry.

You may be one of the individuals who recently received a 52-plus-week lead-time for singlemode fiber cable. Unfortunately, there is no real alternative to this problem. It is the result of a tremendous explosion in demand for singlemode fiber to build up the public networks for the Internet. Fortunately, in the premises industry, singlemode is typically only 10% of the market and its cable lengths are short. So, manufacturers may be able to handle your requirement in special situations. On the downside, however, no one expects this problem to improve significantly until 2003.

Alternative to aramid yarn

One item for which cable manufacturers do have an alternative is the aramid (yellow) yarn used in the manufacture of optical-fiber cable. Aramid yarn is in short supply not only because of the growth in the fiber-optic cable industry, but also because of the growth in other industries that use the product.

The alternate material is fiberglass, which has been used by the fiber-cable industry for years and is an entirely acceptable material for cables-especially for outside plant (OSP) and inside distribution cables. While fiberglass is not a one-for-one substitution for aramid, with modifications to the number of strands of fiberglass used in the cable, the same pull-strength and compression strength can be obtained.

The biggest concern in the field is ensuring that you separate the fiberglass yarn from the fiber-specifically, the white buffered one-prior to cutting off the fiberglass. In addition, because fiberglass does not tie into a knot, you will need to clamp down on the fiberglass with a wire-mesh pulling grip when pulling in cable, rather than tying off to a pulling eye.

Polymer vs. ceramic ferrules

Another item in short supply is the ceramic ferrule commonly used in fiber-optic connectors, such as ST-style and SC. This problem initially reared its head within the OSP industry, specific to singlemode connectors. But now it has made its way over to multimode and the premises industry. Once again, an acceptable solution-the polymer ferrule-has been available for a number of years. Polymer connectors have been viewed as the lower-performing sibling of ceramic connectors, often because of marketing hype within the industry. With material and manufacturing improvements during the last five years, however, polymer ferrule connectors now exceed all TIA/EIA-568B.3 specifications and approach the performance of ceramic connectors.

Extensive testing by AMP Netcon-nect indicates that polymer ferrules are equal in performance to ceramic, not only for insertion loss but also for all parameters-including temperature cycling, durability, and repeatability. Polymer ferrules have seen significant improvements over the years. The precision fiber hole is now achieved by molding technology, and the connector body is now overmolded on the ferrule. For the ST-style and SC connector, the polymer ferrule has been perfected for use with multimode fiber.

The largest impact that polymer ferrules will have on the premises industry is in the supply of patch cords. Once again, the polymer ferrule is not a direct one-to-one substitution for ceramic, but with some minor modifications to manufacturing procedures, such as epoxy application and polishing techniques, a cable-assembly manufacturer can successfully supply patch cords that exceed the requirements of TIA. Of course, a switch to a small-form-factor connector, which is based on polymer versus ceramic, also ensures availability of product.

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Premises fiber-optic cable and connector suppliers are determined to find acceptable ways of meeting industry demand via alternate cable and connector designs. Fortunately, the industry has options, and many manufacturers have perfected two of these solutions. It could be worse. We could be in the OSP industry fighting for singlemode fiber.

Tony Beam is director of fiber-optic operations and business for Tyco Electronics/AMP Netconnect (Harrisburg, PA).

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