Alternatives To Fiber Optic Termination In The Field:
Prepolished/Splice Connectors
The termination of fiber optic cable has always been considered the
most difficult part of installing fiber optics. First you have to deal
with hair thin strands of glass. Then you have to glue a connector on
the end of the fiber and crimp it to the cable. Then, you polish the
ends to get good performance. It’s termination where copper wiring has
always claimed a big advantage over fiber - although terminating Cat 6
is not easy either.
Numerous methods for adhesive/polish connectors have been developed in
attempts to simplify fiber optic termination and speed up the process.
Epoxies that cured overnight were replaced by epoxies that cure in 5
minutes at higher temperatures in an oven. Quick-curing adhesives,
called "anaerobics," can reduce adhesive curing time to less than 5
minutes. 3M has the "Hot Melt" connector that you heat up to melt the
adhesive, insert the fiber and let it cool to set.
Companies have spent many millions developing non-adhesive connectors.
Some crimp on the fiber but still require polishing. Others crimp and
cleave the fiber (cleaving is the process of breaking the fiber under
controlled conditions to produce a end finish in one step.)
Finally, many companies have developed an option worth
considering: prepolished connectors where you splice the fiber into the
connector for termination.
Prepolished splice connectors eliminate the need for
adhesives and polishing for field termination. Instead they use a
factory terminated connector with a stub fiber in the ferrule and a
mechanical splice to terminate the fiber. Termination only
requires preparing the cable, cleaving the fiber, inserting it in the
connector and fixing it with a special tool.
Fiber optic connector manufacturers make prepolished/splice connectors by glueing a short stub fiber into the
connector ferrule and polishing it perfectly with machines in the factory. The back of
the connector is modified with the addition of a mechanical splice,
complete with index-matching gel to reduce loss at the fiber interface
and a crimp to hold the fiber. Terminating these connectors is
super-simple: cleave the fiber, insert it into the connector, crimp it
in place and you are finished. No adhesive, no polish. Terminate a
fiber in less than one minute.
Prepolished splice connectors are very fast terminations but are not
without their downsides. Since there is a mechanical splice and a
connector, the total loss includes one connector plus a splice loss.
Since the splice loss is dependent on the quality of the fiber cleave,
it requires a very precise cleave from a top quality cleaver. Since the
fiber is not attached with adhesive, the attachment strength depends on
a good crimp. The latest generation kits solve most of those problems
so prepolished/splice connectors can now provide a very fast
termination with satisfactory loss if a few precautions are followed.
The economics of prepolished splice connectors is
based on the lower time needed for each termination. The manufacturing
process makes each connector more expensive and the good kits with
quality cleavers are more expensive than adhesive/polish termination
kits, even those with epoxy curing ovens. However, the lower cost of
labor can make these connectors cost effective, especially when only a
few connectors are being used. The secret to lowering costs is getting
high yield of good connectors and that depends on having the right
tools and training - and lots of practice.
These connectors will never have loss as low as an adhesive connector,
since they are actually an adhesive/polish connector with a mechanical
splice inside them so you have both a connector loss and a spice loss.
The good news is the connector factory polish is first class, so the
connector to connector interface has low loss, probably averaging
better than 0.2 dB loss. The bad news is the splice can add 0.3-0.5 dB
to the total loss of the termination, making them a 0.5-0.7 dB
connector at best.
Techs now achieve around 0.5
dB loss from these connectors, using an expensive ($1200) cleaver
typically used with fusion splicers. This cleaver produces consistent,
high quality cleaves to mate with the fiber stub in the connector.
The fiber must be inserted into the connector and kept under
tension during the crimp process, to make sure the two fiber ends in
the internal splice stay in contact. Using these techniques, techs have
been getting excellent yield of connectors that better the TIA-568
standard requirement of 0.75 dB loss or less. Some manufacturers of
prepolished/splice connectors acknowledge these issues, and they now
offer termination kits with precision cleavers and tools that carefully
hold the fiber and connector during the termination process.
Another trick in using these connectors is to visually confirm the
quality of the splice you make in terminating them. A visual fault locator (VFL) with a bright red
laser can be used to optimize the internal splice. The light lost in
the splice is visible through the body of the connector, so one can
confirm the splice is good when the red light is minimized. Adding a
VFL to your toolkit along with a precision cleaver is another necessity.
It’s mandatory to get good training on the termination process for
these connectors, even if you are already familiar with adhesive/polish
connectors. Most manufacturers’ termination kits include special tools
for holding and crimping the connector, as well as that inexpensive
cleaver that we recommend you replace by a really good one. It is
absolutely mandatory to get trained on the use of these tools and the
exact process recommended for termination. And, of course, you should
practice enough with these connectors to become proficient in their use
before bidding or using them on a job.
The
economics of these connectors depends heavily on the yield of good
connectors during installation. When a prepolished connector costs considerably more than an adhesive connector, it is
critical to make sure every connector installed is a good one. That’s
why a quality cleaver, a VFL and a couple of days training is a
worthwhile investment. Only when an installer can equal the yield
of adhesive/polish connectors can a direct comparison of installed
costs be made. Then the advantages of these connectors fast termination
times can be fully exploited to save labor costs in any project.
Unicam termination photo courtesy Corning Cabling Systems.
See the FOA video on prepolished connectors on 
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