Is it time to fine-tune older fiber?

Some fiber optic networks have now been in use for more than 20 years, a tribute to the inherent capabilities of optical fiber. In that same time, copper cabling for premises networks has been through two generations of coax and at least four generations of unshielded twisted pair cabling. It is rare today to find a corporate network still running Thinnet or Token Ring on the original cabling, but there are many fiber networks installed during the same era that are still in use.

Some networks have been upgraded using the same cabling, because many were capable of handling upgrades for network speeds from 10 megabits per second (Mbps) to 100 Mbps and even to 1 gigabit per second. Other networks have just been plugging along at slower speeds because, well, they work just fine as is.

One reason this old fiber still works so well is the extreme care that went into its design. Telephone cable engineers already knew how to make cable that would survive for long times buried underground or suspended from poles. Adapting that technology to glass fibers, while adding plastics to protect the fiber from the environment by hermetically sealing the glass, and using the then-new technology of aramid fibers to prevent stress on the glass itself, led to the creation of fiber optic cables that have lifetimes well over the 20 years of current use.

Another factor in the lifetime of fiber is that it needs no maintenance. Connectors are effectively sealed from dirt in patch panels, and splices are sealed in enclosures that prevent moisture from entering. There is no need to disconnect terminations to clean, inspect or test them. When fiber optic networks were first installed, some users did inspect them, probably out of curiosity, causing problems by allowing dirt to contaminate connectors or overstressing components by handling them.

Fiber optic network equipment has been just about as reliable as the cabling itself. The most likely cause of failure was always assumed to be the transmitter source, a LED or laser, so these devices were designed to be used under the lowest stress possible in the equipment to extend their lives. Many early adopters, such as electrical utilities, had spares programs, so failures of the equipment could be covered by replacing components or complete units, whether or not the equipment itself was capable of being repaired.

Repairing old and obsolete equipment is problematic. Many components used in such equipment have product lives of only three to five years, making repair of older equipment impossible. I remember the problems we had with a product we built at Fotec. It was designed with the first-generation integrated circuits and transceivers of a new network-FDDI-which were replaced on the market in less than two years. For the next eight years, we scoured the shelves of distributors to find these obsolete parts to keep building and supporting products. Finally, we had to cancel the product, because no more parts were available, the network was obsolete and we could not afford to redesign the product for the few customers left. Sometimes you simply cannot repair older products, even if the alternative is a complete network replacement.

Older fiber optic equipment faces another problem caused by the lack of standardization in fiber optic components. Over the lifetime of fiber optic technology, there have been more than 80 different fiber optic connectors manufactured by about as many manufacturers, many of which were proprietary designs. There have also been three different multimode optical fiber types, with core/cladding sizes of 50/125, 62.5/125 and 100/140 microns.

Sometimes you can use your contacts and find the components to fix these older systems. In the last few years that we were in the manufacturing business, we often got calls for obsolete connectors or cables. We would go scrounging in the stockroom, or even the basement, and sometimes were able to find what the customer needed. We also sent them to the original manufacturer, if they were still in business. In one case we knew an engineer at one company who had a desk drawer full of obsolete connectors for just such situations.

Sometimes the users themselves may have stashed away the parts you need. Old patch cords can be used to connect to equipment that uses obsolete connectors while the other end can be terminated in modern connectors to connect to a new cable plant or an older one reterminated in current connector designs.

When faced with an aging fiber optic network, your best bet is to leave it alone. If something does go wrong, fixing it requires time and resourcefulness. It will probably not be cheap either, but it's usually less expensive than throwing everything away and starting over. EC

HAYES is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.