Fiber Optic - Cold Cure Termination

Cold Cure Termination

There are several different methods of terminating fiber cables including heat-cured, cold cured, pre-injected epoxy, UV adhesives and crimped termination's. There are also environmental conditions to take into consideration, but for the purpose of this tutorial we will discuss the cold cure method as it is the most widely used system and probably the easiest to learn. It is also preferable on site as it doesn't require a power source for ovens and fusion splicers.

As with all fiber termination methods, safety is very important so first some safety tips.

* Always work in a clean and tidy area.

* Fiber offcuts are hard to see and can easily penetrate the skin especially if they get into your clothes, so care must be taken to ensure the safe disposal of all offcuts. Dispose of fiber scraps immediately using a suitable container and do not throw into a waste paper bin.

* Because of the dangers of ingesting a fiber, do not eat or drink in the termination area.

* Observe manufacturers recommendations when using solvent based adhesives.

* Never look into the end of a live fiber connector. Holding some multimode fibers up to a piece of paper may prove the presence of light and therefore prove that it is live, but it doesn't prove that it isn't live! Some laser powered equipment use light which is outside of the visible spectrum, so err on the side of caution.

On to the lesson . . . . . .


The Connector

	There are three parts to a fiber connector (four if you count the dust cap) they are: The connector housing, the connector body and the strain relief boot. The body contains the ferrule which aligns the fiber perfectly for mating with another
connector, it's a precision engineered component. The housing contains the fiber body and provides the latching mechanism. The strain relief boot prevents the fiber from bending past the critical point at which it can break.

Preparation

Fill the syringe with adhesive ready to use. Strip back the external sheathing of the cable using a rotary stripping tool. Cut back the aramid strength member using ceramic or kevlar scissors. Slide the strain relief boot onto the fiber to be terminated. Strip the primary buffer from the fiber using fiber strippers not ordinary wire strippers.
Do this a small section at a time to prevent the fiber breaking, about 10mm (3/8 in) on each cut is fine until you get used to it. Strip back about 30mm (1.25 in).

"Sticking" on the connector!

Inject the adhesive into the connector body until a small bead appears at the end of the ferrule. Clean the bare fiber with a lint free wipe and isopropyl alcohol, it will "squeak" when it is clean. Apply the primer to the bare fiber either with the brush supplied or by dipping it into the bottle. Push the fiber in to the connector body in one smooth action until you feel the buffer reach the back of the ferrule.

The chemical reaction between the adhesive and the primer happens almost instantly so don't stop while inserting the fiber otherwise it will stick before it is fully home.

Cleaving

The purpose of cleaving the fiber is to ensure that it breaks cleanly at 90 degrees, although you may think that because it is ground down to the ferrule and then polished it wouldn't make any difference if it were just snapped off! It makes a big difference. If the fiber shatters or splinters down past the ferrule then no amount of polishing will turn it into a good connection. A hand held scribe or pen cleaver is adequate for this job, unlike fusion splicing where a perfectly cleaved end is essential for a good connection.

Lightly scribe the fiber as close to the ferrule as possible and use a slight tug to break the fiber end away. Dispose of the fiber offcut immediately in the hazardous debris container.

Polishing

The first step in polishing is to take the fiber down to the ferrule, for this we use about a 9 micron lapping film. Hold the connector in one hand and rub the nub of fiber down to the ferrule with the lapping film. When it is close enough you will feel it get smoother. Step two. Insert the connector into the polishing puck, this keeps it perpendicular to the polishing surface. Place a sheet of 2 micron lapping film on a suitable flat surface.

Hold the connector and puck, and place it on the polishing surface. Then move it in a figure of 8 pattern about 30 times using slight pressure. The end is now polished and can be inspected with the microscope. Some people recommend 3 or 4 stages of polishing but we find that we get just as good results from just these two grades of abrasives.

Visual Check

Using the illuminated microscope check that the polished end is OK. Things to look out for are excessive scratches or remnants of the epoxy adhesive. You can now fit the housing and dust cap. Testing Once both ends are terminated the fiber can be tested. Fiber testing used to involve a bulky OTDR (Optical Time Domain Reflectometer) operated by a geek with a degree in optical physics, but these days a simple hand held light source and power meter can be used. To give it a full test you can also use a fiber certification tools which simply tells you what systems the fiber is good for. These simple to use (but quite expensive) instruments will give a print out of all test parameters and losses as well as the communications media it will work on.