We’re nearing the end of our fiber optic cable plant installation; cable has been placed and spliced, so we’re ready to terminate the fibers for connections into patch panels or equipment. The location and types of connectors (generally SC, ST or LC) should have been decided during the design phase of the project. Outlets and rack or wall-mounted patch panels should be installed and ready for the termination of the cables.
(Note: part 9 is here.)
Since the development of fiber optics, some have considered termination the most difficult step of installation, and as a result, manufacturers have spent more time developing terminations than any other component. This has made termination much easier, and the yields of field-terminated connectors have become very high.
The customer sometimes specifies a brand of connector and termination method, or a manufacturer may require a specific connector to maintain cabling warranty coverage. If the method specified is not familiar to the contractor, it is vital to get trained on that installation method ASAP. If not, and the decision on what process to use falls on the contractor, always choose the proper termination equipment and a method with which you have experience.
Besides having the right termination tools and experience with the method being used, it’s important to have the correct termination supplies. Adhesives used for adhesive/polish connectors should be fresh and within the manufacturer’s expiration date, and new polishing film of the proper grit is necessary to get good finishes. Even if the terminations will use prepolished/splice connectors, they should be of the latest styles, as these connectors have improved tremendously in recent times. Even the termination kits have been upgraded by most manufacturers to improve connector losses and yield.
If termination involves fusion-splicing pigtails on single-mode fibers, the pigtails should be checked to ensure they are of high quality. It is generally better to buy patchcords, which are easily tested, and to cut the patchcords in half to make pigtails for splicing.
The cost of terminations is a large part of the cost of any fiber optic installation. Three factors affect the cost of terminating an optical fiber. First is the cost of the connectors, including the required supplies, such as adhesive or polishing film. Second is the labor time required for making each termination and testing it. Last, and sometimes the most important issue, is yield or how many connectors test as good.
A good connector is one that has an acceptable loss and ensures the end-to-end loss of a cable meets the calculated loss budget. TIA 568 currently says that any connector can have a loss of 0.75 dB, a carryover from almost 20 years ago when the standard was written to cover any connector, including prepolished/splice connectors of that era. That loss number is being questioned in the TIA committees and is expected to be revised downward. For today’s prepolished/splice connectors, 0.5 dB is a reasonable number. Adhesive/polish connectors should be lower, perhaps an average of 0.3 dB.
Every connector that does not produce good test results must be replaced, therefore costing not only the direct time of termination but also the time to set up termination gear on the job site for the second time, to redo the termination and then retest the fiber. Even 90 percent yield of good connectors means the cost of termination is more than 110 percent as much as the estimated cost of one connector.
Obviously, it is vital that the installer be skilled at making terminations. However, there is another option: installing a prefabricated cabling system, that requires no termination at all. This option is becoming more popular, since it saves installation time and avoids the uncertainties of yield in termination, but it requires more care in cable installation and almost as much testing. However, its use must be decided on at the design phase, long before installation.
At the termination phase, terminated fibers must be correctly arranged in patch panels according to the color codes of the fibers as covered in the cable plant documentation. When the fibers are connected to the back side of the patch panels, they must follow the color codes and documentation so that each jack on the patch panel connects to the proper fiber. This will create a path from the transmitter of one piece of communications gear to the receiver on another.
Now, the cable plant is installed; it’s time to test it. That’s an important step involving more than I can cover in one column. So next month, I will start a new series, “Testing the Fiber Optic Cable Plant.”
HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.JimHayes.com.