Since fiber optics is growing in market share for all kinds of applications, I am hearing more stories about problems with installations. At The Fiber Optic Association, I handle most of the technical inquiries, so I tend to see the trends develop. For a long time, it was testing issues—especially optical time-domain reflectometer (OTDR) testing by inexperienced operators—but I recently have been seeing a lot of connector problems.
Most of these problems are high-loss connectors caused by poor termination techniques, especially polishing, that anyone can identify with visual inspection. These problems should not exist and are caused by lack of installer training or practice or supervisors and customers misunderstanding what is a good or acceptable fiber optic connector.
Fiber optic connector manufacturers have been working for more than 30 years to make terminating optical fiber easier, faster and cheaper, and they have done a really good job. But, perhaps, they have been overselling the simplicity of fiber optic termination.
Manufacturers have invented and tested many different ways of attaching a connector to that hair-thin strand of glass, including various methods of gluing, crimping and clamping. However, the best method is using epoxy or anaerobic adhesives, followed by polishing.
Factories terminating fibers use heat-cured epoxies because they produce the most reliable connectors. They also generally use polishing machines instead of hand methods to get more consistent results. Heat-cured epoxies are not used as often in the field; they require ovens, and most ovens are not easily portable.
Many installers still use Hot Melt connectors. These come with the adhesive preloaded and are heated in a special oven to a much higher temperature than necessary for curing epoxy.
Anaerobic adhesives do not require heat curing but are harder to use. Some methods use a chemical to speed up the process, but sometimes it is too fast for installers to use easily.
Heat-cured epoxy and Hot Melt connectors have one big advantage over anaerobics: there is a small bead of cured epoxy on the end of the connector that makes polishing much easier.
Polishing is a process installers need to learn and practice. While I hesitate to say connector polishing is an art and not a science, it’s certainly true that there are a lot of differences in techniques, which can be confusing.
Thirty years of experience in fiber optics and feedback from the hundreds of instructors I have trained have shown that developing basic skills makes field termination faster and cheaper. Keeping those skills current requires practice, something some installers and contractors forget.
To master the processes and develop the techniques, you must first understand what makes a good connector. If you ask the question of most installers, they will say a good connector tests as low-loss.
Sometimes, they quote the TIA 568 standard loss of 0.75 decibels (dB) as the value that is acceptable. Ain’t so. Even TIA understands that a good connector is not a 0.75-dB-loss connector. The association is, therefore, agonizing over how to redefine it, which will likely be as a graded system that defines connectors down to 0.1–0.2 dB, a reasonable value for field-installed polished connectors.
While testing for loss is required for accepting the connectors, it’s something that few installers or contractors understand well. However, a simple visual inspection is something everyone can understand.
A properly installed fiber optic connector, which has been carefully polished, is smooth and free of scratches, cracks, pits or any other defect. If a connector looks good, it’s 99 percent likely to test as good, meaning low loss.
Looking at connectors is easy and cheap. You can buy a good microscope for less than $200, well within any contractor’s budget. Every installer and user should have one. If you can afford it, a video microscope is even better, as it allows several people to see the connector at one time and to store photos for documentation.
That microscope will get a lot of use. It should be used to inspect connectors for dirt and contamination before connecting to another connector or equipment.
Full disclosure: I invented a portable oven long ago (it is still in production) that makes field use of epoxies easier. I also developed an anaerobic adhesive method that offers higher reliability. I intend to discuss these and polishing techniques in future columns.