Low loss is still a big issue

Terminating optical fibers by attaching connectors with epoxy adhesive and polishing the ferrules seems like an anachronism. That was how we started almost 25 years ago, so surely better methods have been developed by now. You can get preterminated cable assemblies that need no field termination at all. You can get prepolished/splice connectors you splice onto the fiber. There are anaerobic, quick-set and 3M Hot Melt adhesives that set quickly but still require polishing. And there are crimp-and-cleave connectors that require no polishing at all.

But every factory-terminated connector still uses the epoxy/polish method of termination. Why? It’s simply a matter of performance, reliability and economics. The epoxy/polish type of connector provides the lowest loss, greatest reliability, highest yield and lowest cost of any termination type.

For single-mode fiber, it is virtually the only method of termination that can provide the precise end finish necessary for the low loss and minimal back reflection required for high-speed networks. Almost all single-mode connectors are factory made with epoxy adhesives and machine polishing. Field terminations are accomplished by fusion splicing on a factory-made pigtail. Field terminations of single-mode are possible using anaerobic or prepolished/splice connectors, but the higher back reflection common with field terminations are likely to be a problem with today’s multiGigabit networks.

Termination of multimode connectors is much less critical, especially where back reflection is concerned. But low loss is still a big issue, especially since multimode premises networks often have several patch panels and patchcords between transmitters and receivers and the maximum tolerable link loss for high speed networks like gigabit Ethernet and Fibre Channel is quite low. If an installed network has two intermediate connections and two patchcords with all connectors near the maximum loss allowable in the TIA 568 standards—0.75 dB—the link loss will exceed the maximum loss in some gigabit network standards.

With typical losses of field-terminated epoxy/polish connectors around .2 to .3 dB, meeting loss budgets is easy. A well-trained technician using a portable epoxy curing oven can get almost 100 percent yield, reducing the cost of replacing connectors that fail insertion loss tests. The real secret behind the epoxy/polish connector is the small bead of epoxy that you create on the end of the connector ferrule when you inject the adhesive. It creates a hard extension of the ferrule that holds the fiber perfectly for quick and easy polishing.

What about the other types of connectors or processes that promise faster and easier termination? Well, the time it takes to put the connector on the fiber is not the only time to consider. The installer must set up at the work site, install the patch panel and any other hardware and prepare the cable for termination before actually putting the connector on the fiber itself. After termination, the cable must be connected into the patch panel and tested then bad terminations fixed and retested. After all connectors are tested good, the work area must be cleaned up and all the tools repacked.

Those selling quick-connect connectors show you how easy it is to put a connector on one fiber in a minute or less. But they forget to mention all the other activities at the work site. And they only consider one connector. If you are terminating, for example, a 24-fiber cable with epoxy/polish connectors using a curing oven in a “production line,” the effective termination time is only a couple of minutes anyway. You inject epoxy into several connectors at one time, strip a fiber and attach a connector, then put it in the oven to cure for 5 minutes or so. While it cures, you attach more connectors. By the time you fill the oven up, the first one is cured and ready to polish. If you have more to do, you replace it in the oven with another ready to cure until all are cured, then you polish them all at once, at about a minute each. With this process, the epoxy curing time becomes irrelevant.

Which brings us to the bottom line. Connectors for epoxy/polish terminations are available today in quantity for not much more than $1 each. Quick-connect connectors sell for 5 to 15 times more, depending on the type and quantities. When the total cost of termination is properly calculated, including the realistic time necessary to set up before making terminations and cleaning up afterward, saving a few minutes labor per connector is highly unlikely to offset the higher cost of the connector itself.

So are epoxy/polish connectors obsolete? Not on your life. Many smart contractors still use them and end users still specify them, knowing they are still the highest quality solution to fiber optic termination.

Want to see exactly how to do an epoxy/polish termination? See www.LennieLightwave.com for the “virtual hands-on” termination tutorial. EC

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