Missed Connections

In the early days of fiber optics, the biggest complaint was about the difficulty of installing connectors. You had to mix epoxy and inject it into the connector. Then you had to let the adhesive cure overnight or use a bulky curing oven. The polishing process was complicated and different for every connector type. Over time, the industry has developed new techniques and tools to make the termination process much easier and quicker.

Many complaints went away when fiber optic connectors changed from metal or plastic ferrules to ceramic ferrules in the mid-1980s. Ceramic ferrules were more precise, so there were fewer problems with the fiber fitting in the connector ferrule properly. Since ceramics stuck better to the adhesives used with glass fibers, the problems of fibers coming loose in the connectors were eliminated, but the ceramic ferrule’s biggest advantage was that it was as hard as the glass of the fiber. As a result, it was easier and quicker to polish properly, unlike metal or plastic ferrules that tended to get unevenly polished.

The next step was to improve the tools and termination process. Connector companies started with new choices in adhesives and then developed new processes and tools that would make termination easier. Along the way, many mistakes were made, but, in the end, termination has become much easier.

Many tried substitutes for two-part epoxy. UV-curable adhesives worked well, but the expensive light required for curing was dangerous to human eyes. 3M introduced the Hot Melt connectors where the adhesive already in the connector was melted by a special oven. Hot Melts are still widely used today.

Several acceptable techniques used quick-setting acrylate adhesives from the same family as Krazy Glue. Some methods still used syringes to inject the acrylate adhesive. Most methods required a second chemical to set the adhesive, but unless carefully applied, it often worked so fast the fiber could not be fully inserted in the connector before the glue set, ruining the connector. Another method I helped develop used a simple adhesive (Loctite 648) that you simply wiped on the fiber with the applicator tip of the bottle. You then inserted the fiber in the connector and let it set for about 5 minutes before polishing.

I also helped develop an inexpensive portable epoxy-curing oven that looks like the cylinder of a revolver pistol. It could cure epoxy in 5 minutes. Either the epoxy-curing oven, Hot Melt oven or quick-setting adhesives allowed easy field termination and were practically the only methods used until the prepolished ­splice connectors became good enough for field use, a method I will discuss in a future column.

Polishing was the next problem. Variables included the methodology, types of polishing film, and pucks to hold the connector and the polishing surface. Some manufacturers recommended two-step processes while others recommended three, and few agreed on the types (grit) of polishing film to use. Some recommended plastic polishing pucks, others metal. Some said to polish on a glass plate, others said rubber.

In the end, a three-part polishing process proved best. For the first polish, an air polish was recommended with a 12-micron grit aluminum oxide film. The technician would hold the connector in one hand and the polishing film in the other, and the process was to grind down the fiber with the coarse film until it was almost level with the end of the connector, which you could feel with your finger. Then, the technician cleaned and inserted the connector into the polishing puck­—typically made from hard, glass-filled plastic that would leave the least amount of residue on the polishing film. Since the end of the connector ferrule was now a convex round surface, the polishing was done on a flat plate (glass or plastic) with a thin rubber pad that deformed to allow the end of the ferrule to be polished to the proper round radius. Polishing in two steps using medium and fine polishing films (3 and 0.3 micron grit) with a quick cleaning between each step produced a fine finish in just a couple of minutes.

With the right tools, including the fiber stripper you like best (see last month’s column), a little bit of training and some practice, a technician can install these adhesive/polish connectors in the field quickly and with virtually 100 percent yield to acceptable loss.

I’m amused when people declare that “nobody polishes connectors anymore,” implying that the quick-terminating prepolished splice connectors are what everybody uses. Not so. Every factory-made patchcord uses epoxy/polish techniques, typically with machine polishing. Many installers still use epoxy/polish in the field, especially when connectors are installed in adverse environments.

While it’s true that many installers now depend on the prepolished/splice style of connector, successfully installing these connectors also depends on understanding which tools to use and following the processes exactly. That’s the subject of my next column on tools.

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor
Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com .

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