What are the ways of fiber termination

Optical fiber has long been regarded as the "black art" in the field of data installation. Some installers deliberately choose to specialize in fiber installation/termination because it requires additional skills, training, and equipment, so they can add some value to the business. So, what are the ways of fiber termination?

Fiber Termination

1. Direct termination

Direct termination refers to attaching a connector to the end of each horizontal cable.

1.1 Oven cured epoxy type terminations

This is the most common (and earliest) direct termination method. It uses standard connectors, epoxy and a variety of sanding papers, depending on the manufacturer. This method first removes the buffer layer, cleans the bare fiber, and prepares the fiber. The epoxy resin (binder and catalyst) is then mixed and transferred to a syringe. The epoxy is then injected into the ferrule of the connector until the epoxy appears on the end face. The fiber was then inserted into the ferrule, then the ferrule was placed in the ferrule, and after about 5 minutes, it was placed in a drying oven. After drying and cooling, the sleeve was removed and the fiber ends were cut off. Then sand, clean and inspect.

1.2 Pre-assembled epoxy type terminations

The termination method for this type of connector is similar in most places to traditional oven-cured epoxy. It comes pre-filled with pre-mixed epoxy and can additionally be re-melted (though not recommended by the manufacturer) to remove and replace broken fibers.

1.3 Cold curing epoxy type termination

The prep work is the same as for oven cured epoxy, but simplified. Preparation is the same as oven cure, but catalyst and adhesive are typically placed directly from the dispenser onto the fiber or ferrule without mixing/transfer to syringes or injection of ultra-high viscosity epoxy resin. At room temperature, the cure time is typically about 2 minutes because the adhesive is anaerobic (cures in the absence of air). After cutting the fiber, grind, clean and inspect.

1.4 Mechanical bending and grinding

There are a number of mechanical bending and polishing methods that use the working principle of mechanical bending to hold the fiber in the ferrule. Before inserting the ferrule, remove the buffer layer and clean the fiber. The fiber is then "bent" (using a mechanical jig) into place, then the fiber is cut and polished.

1.5 Mechanical bending with pre-ground ferrules

The ferrule of this connector has a small length of fiber that has been polished at the factory. There is a certain space behind this small length of fiber, which has been filled with a gel that matches the refractive index of the light. The fiber is then stripped, cleaned, cut to a predetermined length, inserted into the ferrule, and bent into place in a similar manner to the previous connector.

2. Splice termination

Splice is the connection of fiber optic coils (shipped with a connector on about 1 meter of bare fiber at the factory) to the individual fibers of the horizontal fiber. Regardless of the splice type, fiber preparation involves stripping the buffer, cleaning the glass, and cutting the fiber to the desired length. When cutting the fiber, a right-angled end face must be maintained to closely align the fiber end. It is also possible to join two cables together using a splice, which typically connects an outdoor cable with an indoor cable.

2.1 Mechanical bonding

This is (usually) plastic moulding with cable clips (or keyed locking clips) on each end, suitable for 250 or 900m cushioning. The fiber is prepared in the same way as above, with the ends slid inside the mold until the ends meet in a space usually filled with a gel that matches the index of refraction.

2.2 Fusing Bonding

This method requires the use of a fuse bonder. The fusion splicer includes an alignment device, an arc generator and a small drying oven. Alignment equipment ensures that the prepared fiber is in the corresponding position on each axis. The arc then fires at a pre-programmed time and power for a seamless connection. If the connection is fragile (m diameter in the case of welded glass), a heat shrink sleeve with stainless steel reinforcement rods can be installed.

3. Pre-terminated fiber

With this technology, the installer can specify the length, number of cores, cable structure and connector form, and the user simply pulls the cable to the appropriate location and connects it inside the enclosure, no other operations are required. The pre-terminated cables are protected by pull-in holes at both ends and have been optically tested by the manufacturer. A slightly different pre-terminated fiber uses a plug-in distribution box instead of a patch panel, with a multi-core connector (MTP/MPO) on the back and SC, ST, etc. connectors on the front. Fastest installation because both cable assemblies and distribution boxes are pre-tested.

3.1 Multimode fiber or single mode fiber?

Not all of the above termination methods are applicable to single-mode fibers, but all of them are applicable to multi-mode fibers. This is due to the end face grinding that occurs in the termination, providing acceptable return loss performance. In any connector with a pre-polished ferrule, its return loss will be controlled during the manufacturing process. Splices also use factory-installed connectors that provide verified return loss values. Obviously, the pre-terminated fiber also passed the test at the factory.

make a selection

As with any choice in everyday life, there are pros and cons to termination. The pros and cons of each of the above terminations will be discussed here so that you can make an informed choice, or at least ask the relevant manufacturer to answer some questions.

1. Direct termination

1.1 Epoxy type termination method for drying oven curing

Reliable old-fashioned method, easy to learn, but now obsolete. Squeeze the epoxy into the syringe, stick the syringe to the table, and quickly bake your hands after the ferrule sleeve is placed in the drying oven? Success? Although the purchase price is low, the installation cost is not low.

1.2 Pre-installed epoxy type termination method

It's the perfect evolution of the reliable old-fashioned method. Eliminating the troublesome epoxy filling job is of course a good thing. Connectors are more expensive because it reduces installation time.

1.3 Cold curing epoxy resin type termination method

This approach has been embraced by many. Anaerobic adhesives have been widely used in outdoor environments with great success. It has also been successful in the fiber optic connector environment. The glue might be a little dirty, but no more baking your hands. In addition, the grinding process is very easy because there is no need to remove a large piece of epoxy on the end face of the ferrule. Plus, it doesn't require the use of a dry box or power source.

1.4 Mechanical bending and grinding

This is another very popular method for installers looking for an easy termination method. There are concerns about the mechanical properties of the unsupported fiber within the ferrule and the effects of temperature fluctuations (ask your sales rep for the "piston" effect).

1.5 Mechanical bending with pre-ground ferrules

Probably the easiest solution with connectors. There is no "piston" problem because the fiber is matched to a stub using a gel with the corresponding index of refraction. People have been using this solution in field termination.

People usually go with MT-RJ connectors because there is no really satisfactory alternative. These connectors are generally more expensive because of the complex manufacturing process.

2. Splice termination

2.1 Mechanical bonding

This is a lesser valued fiber termination method, typically used in petrochemical/petroleum refining and manufacturing environments where "undesired" open flames (or arcs). The general attitude is that this method is only suitable for temporary repairs, but in fact, it has been used in harsh environments for a long time without degrading optical communication performance at all.

2.2 Fusing Bonding

The most versatile termination method that introduces the least loss in all types of fibers. Equipment purchase costs are (relatively) high, but prices are falling. As long as the fiber optic coils used are of good quality and the operators are trained and experienced, I personally like this approach very much. Installation of single-mode fiber is easy because the return loss is tested at the factory and most splicers will provide a splice loss estimate.

3. Pre-terminated fiber

This is probably the easiest method for installers who are not fiber savvy. Possible issues include damage to the fiber during insertion, whether to test the polarity of the connection, accurately estimate the length of the link, and whether the optical communication test service still needs to be subcontracted.

That's all for fiber termination in detail, and as you can guess, there are many different ways to terminate fiber optic cables. As mentioned earlier, these approaches each have their own advantages and disadvantages, which ultimately depend largely on the environment, the application, and generally the installation cost.