In several recent columns, I discussed the process of fiber optic terminations. I examined each step in detail and shared some of the things I have learned from experience and teaching students. As they say, one learns from one’s mistakes.


Last month, we stripped the fiber we planned to terminate, so we are almost ready to attach the connector. But first, we have to clean the fiber to remove any dirt and scraps of the stripped buffer. Since we are dealing with such small components, cleaning is one of the most important tasks in fiber optics. Cleaning the fiber before inserting it into a connector does not just involve cleaning; it must be done in a way that does not adversely affect the adhesive we use in the connector.


Most manufacturers of connectors and adhesives for fiber optics recommend using a lint-free wipe and pure isopropyl alcohol, which is 99 percent pure and quite different from typical drugstore isopropyl rubbing alcohol, which is 70 percent alcohol and 30 percent water. 


The water in rubbing alcohol is bad for fiber and adhesives. Water migrates into the glass fiber and can affect strength and attenuation. Water also can affect the strength of adhesives used in the termination process and the length of time it takes some adhesives to cure.


I found this out the hard way. I was teaching students using supplies provided by a distributor and discovered the anaerobic adhesive would not harden. I recognized that the alcohol wipes I had received were medical wipes, the ones a nurse uses to disinfect your skin before an injection. The moisture content of the rubbing alcohol prevented the adhesive from hardening. Switching to the correct alcohol wipes solved the problem.


Once we have the proper products, we can set aside our clean fiber and prepare the connector for termination. Be sure to place the fiber in a clean location (on top of a clean, lint-free wipe is good) and somewhere you won’t touch it by mistake.


Since we are focusing on adhesive-polish connectors, we have three types of adhesives to consider, each requiring a different technique. Epoxies are usually heat-cured, but some types set overnight at room temperature. Heat-cured epoxies are used for factory-made patchcords because of their ease of termination and high reliability. 


Epoxies are easier to use because the connector will have a small bead of adhesive on the end of the fiber that supports the fiber during the cleaving and polishing process. This support makes it nearly impossible to get a poor cleave and polish.


The drawback of the epoxy-termination method is you need a curing oven. While they are not expensive, almost all of them require power at the work site; there is only one battery-powered oven (I designed it 20 years ago).


Anaerobic adhesives are simpler to use but harder to get right. The adhesives can cure in about 30 seconds with a two-chemical system that pairs the adhesive with a setting agent, or in about 5 minutes for an adhesive alone. The drawback is you do not have the adhesive bead on the end of the connector supporting the fiber, so you have to be more careful when cleaning and polishing. 


The 3M Hot Melt connector comes with the adhesive inside the connector. A high-temperature oven melts the adhesive so you can insert the fiber. These connectors also have the adhesive bead on the end of the ferrule to make them almost foolproof to cleave and polish. If you mess up a Hot Melt connector, you can usually reheat it and try again.


The choice between these three types of connectors is really a matter of personal experience and economics. I have found that students often prefer to use what they learn in class when in the field. Those of us who have tried all of them generally agree that the epoxy and Hot Melt methods are easier, but an analysis of termination time and cost makes the anaerobic or epoxy methods cheaper, mainly because the connectors themselves are much cheaper.


Some installers prefer to avoid the adhesive-polish connectors entirely. Instead, they use the prepolished-splice connectors that are sold on the premise of quick termination. Don’t be fooled. The Fiber Optic Association has done time and motion studies of fiber optic termination, and the speed claims don’t always make sense. By the time you go to a work site, do your setup, make the terminations, clean up and leave, the type of termination hardly affects the time it takes for the whole job.


Next month, the process continues.