Terminating Fiber With Splice-On Connectors

In my August 2017 column, I discuss the history of fiber optic connector termination and a new technology, splice-on connectors (SOCs). At that time, I wrote, “These connectors, now known as splice-on connectors, may well become the dominant field-termination method. They are faster, cheaper and easier with better performance—what more could you ask for?"

Since then, more manufacturers have introduced SOCs, and we’ve been incorporating them into Fiber Optic Association (FOA) training programs. Now is a good time to look at the SOC process compared to other options and evaluate its advantages and disadvantages.

Most factory-made connectors, such as on pigtails you purchase from a distributor, are epoxy/polish terminations. The fiber is glued into the connector ferrule with a heat-cured epoxy, and the end of the ferrule is polished in a three-step process as shown in the photos below. In factories, the polishing is generally done on a large machine that polishes dozens of connectors at a time.

Adhesive/polish termination steps
Adhesive/polish termination steps

Adhesive/polish connector termination can also use quick-setting or HotMelt adhesives instead of epoxy, but the process is similar.

For many years, these types of connectors were the standard for all terminations, but they were messy, required special skills and took time. Several other termination methods were tried—crimp and polish, crimp and cleave and finally prepolished/splice connectors.

Prepolished/splice connectors had a connector that had been factory terminated with a short fiber and a mechanical splice just behind the ferrule. The termination process was simpler—cleave the fiber, push it into the splice, and crimp or lock it in place. Below I demonstrate the process using a Corning Unicam toolkit.

Prepolished/splice connector process with Corning Unicam
Prepolished/splice connector process with Corning Unicam

Prepolished/splice connectors had the advantage of being quicker and easier than adhesive/polish terminations but had several disadvantages. Even though you had a nice polished end on the ferrule that should have low loss when connected to another connector, the assembly includes a mechanical splice that adds at least 0.1 to 0.3 dB loss to the connection. If you don’t make a good cleave on the fiber, the loss of the mechanical splice can be a lot more, enough to cause failure of the connector. Finally, if the crimp holding the fiber is not secure, the connector can fall off or the fiber can pull out and cause high loss.

Just a few years ago, a better termination method was developed. Instead of a mechanical splice, these connectors use a fusion splice. The connector has a short (~2-inch/50-mm) fiber pigtail. You prepare the fiber to terminate as usual (strip, clean, cleave) and place it in the splicer. Then you repeat with the fiber pigtail on the connector. The two fibers are fusion spliced, and a heat shrink splice protector is applied to the splice joint.

SOC connector process
SOC connector process

An SOC has several advantages over connectors with mechanical splices. A fusion splice has very little loss, so it does not add noticeably to the connector's loss. Fusion splices are also much more reliable than mechanical splices. And so far, all the splice-on connectors we have seen also cost much less than the connectors with mechanical splices.

Another comparison is to fusion splicing ~1 meter long pigtails on to a fiber for termination, widely used in the past for single-mode fiber. These pigtails require much more space and hardware than SOCs since the fusion splice needs a separate protector, splice tray and either a splice closure or patch panel.

When most techs hear about SOCs, they immediately assume the total cost is higher because you need a fusion splicer. While you do need a fusion splicer, there are new, inexpensive, portable splicers (like the EasySplicer shown above) made for cost-sensitive markets (e.g., fiber-to-the-home) that are comparable to the best kits for prepolished/splice connectors.

In addition, every splicer that does SOCs will do regular splices, so having a splicer is something that every contractor and installer needs anyway. If you are buying a new fusion splicer, just make sure you choose one that does SOCs and compare prices of the company’s connectors before you buy.

The FOA recently trained several groups of techs and instructors on SOCs, so I can say with authority that it’s something a fiber tech can learn quickly and get almost 100 percent good connectors. Everybody, especially those of us who have done many other types of termination, seems to agree that this is the simplest and best way to terminate fiber.

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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