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Preparing Fiber Optic Cable For Splicing or Termination

by:TBT     2020-08-15
I recently watched my coworker disassembling a computer using only one tool. Was it the right tool for the job? Yes and no. It was the tool he had... it worked, however, there is definitely more than one tool out there that would have made the task easier! This situation is definitely one that many fiber optic installers know all too well. As a gentle reminder, how many of you have used your Splicer's Tool Kit (cable knife/scissors) to remove jacketing or even slit a buffer tube and then use the scissors to hack away at the Kevlar? Did you nick the glass? Did you accidentally cut through the glass and have to start over?
Correctly splicing and terminating fiber optic cable requires special tools and techniques. Training is important and there are many excellent sources of training available. Do not mix your electrical tools with your fiber tools. Use the right tool for the job! Being proficient in fiber work will become increasingly necessary as the importance of data transmission speeds, fiber to the home and fiber to the premise deployments continue to increase.
Many factors set fiber installations apart from traditional electrical projects. Fiber optic glass is very fragile; it's nominal outside diameter is 125um. The slightest scratch, mark or even speck of dirt will affect the transmission of light, degrading the signal. Safety is important because you are working with glass that can sliver into your skin without being seen by the human eye. Transmission grade lasers are very dangerous, and require that protective eyewear is a must. This industry has primarily been dealing with voice and data grade circuits that could tolerate some interruption or slow down of signal. The person speaking would repeat themselves, or the data would retransmit. Today we are dealing with IPTV signals and customers who will not tolerate pixelization, or momentary locking of the picture. All of the situations mentioned are cause for the customer to look for another carrier. Each situation could have been avoided if proper attention was given to the techniques used when preparing, installing, and maintaining fiber optic cables.
With that being said, why don't we review basic fiber preparation? Jacket Strippers are used to remove the 1.6 - 3.0mm PVC outer jacket on simplex and duplex fiber cables. Serrated Kevlar Cutters will cut and trim the kevlar strength member directly beneath the jacket and Buffer Strippers will remove the acrylate (buffer) coating from the bare glass. A protective plastic coating is applied to the bare fiber after the drawing process, but prior to spooling. The most common coating is a UV-cured acrylate, which is applied in two layers, resulting in a nominal outside diameter of 250um for the coated fiber. The coating is highly engineered, providing protection against physical damage caused by environmental elements, such as temperature and humidity extremes, exposure to chemicals, point of stress... etc. while also minimizing optical loss. Without it, the manufacturer would not be able to spool the fiber without breaking it. The 250um-coated fiber is the building block for many common fiber optic cable constructions. It is often used as is, especially when additional mechanical or environmental protection is not required, such as inside of optical devices or splice closures. For additional physical protection and ease of handling, a secondary coating of polyvinyl chloride (PVC) or Hytrel (a thermoplastic elastomer that has desirable characteristics for use as a secondary buffer) is extruded over the 250um-coated fiber, increasing the outside diameter up to 900um. This type of construction is referred to as 'tight buffered fiber'. Tight Buffered may be single or multi fiber and are seen in Premise Networks and indoor applications. Multi-fiber, tight-buffered cables often are used for intra-building, risers, general building and plenum applications.
'Loose tube fiber' usually consists of a bundle of fibers enclosed in a thermoplastic tube known as a buffer tube, which has an inner diameter that is slightly larger than the diameter of the fiber. Loose tube fiber has a space for the fibers to expand. In certain weather conditions, a fiber may expand and then shrink over and over again or it may be exposed to water. Fiber Cables will sometimes have 'gel' in this cavity (or space) and others that are labeled 'dry block'. You will find many loose tube fibers in Outside Plant Environments. The modular design of loose-tube cables typically holds up to 12 fibers per buffer tube with a maximum per cable fiber count of more than 200 fibers. Loose-tube cables can be all-dielectric or optionally armored. The armoring is used to protect the cable from rodents such as squirrels or beavers, or from protruding rocks in a buried environment. The modular buffer-tube design also permits easy drop-off of groups of fibers at intermediate points, without interfering with other protected buffer tubes being routed to other locations. The loose-tube design also helps in the identification and administration of fibers in the system. When protective gel is present, a gel-cleaner such as D-Gel will be needed. Each fiber will be cleaned with the gel cleaner and 99% alcohol. Clean room wipers (Kim Wipes) are a good choice to use with the cleaning agent. The fibers within a loose tube gel filled cable usually have a 250um coating so they are more fragile than a tight-buffered fiber. Standard industry color-coding is also used to identify the buffers as well as the fibers in the buffers.
A 'Rotary Tool' or 'Cable Slitter' can be used to slit a ring around and through the outer jacketing of 'loose tube fiber'. Once you expose the durable inner buffer tube, you can use a 'Universal Fiber Access Tool' which is made for single central buffer tube entry. Used on the same principle as the Mid Span Access Tool, (which allows access to the multicolored buffer coated tight buffered fibers) dual blades will slit the tube lengthwise, exposing the buffer coated fibers. Fiber handling tools such as a spatula or a pick will help the installer to access the fiber in need of testing or repair. Once the damaged fiber is exposed a hand- stripping tool will be used to remove the 250um coating in order to work with the bare fiber. The next step will be cleaning the fiber end and preparing it to be cleaved. A good cleave is one of the most important factors of producing a low loss on a splice or a termination. A Fiber Optic Cleaver is a multipurpose tool that measures distance from the end of the buffer coating to the point where it will be joined and it precisely cuts the glass. Always remember to use a fiber trash-can for the scraps of glass cleaved off of the fiber cable.
When performing fusion splicing you will need a Fusion Splicer, fusion splice protection sleeves, and isopropyl alcohol and stripping tools. If you are using a mechanical splice, you will need stripping tools, mechanical splices, isopropyl alcohol and a mechanical splice assembly tool. When hand terminating a fiber you will need 99% isopropyl alcohol, epoxy/adhesive, a syringe and needle, polishing (lapping) film, a polishing pad, a polishing puck, a crimp tool, stripping tools, fiber optic connectors ( or splice on connectors) and piano wire.
When a termination is complete you must inspect the end face of the connector with a Fiber Optic Inspection Microscope. Making sure that light is getting through either the splice or the connection, a Visual Fault Locator can be used. This piece of equipment will shoot a visible laser down the fiber cable so you can tell that there are no breaks or faulty splices. If the laser light stops down the fiber somewhere, there is most likely a break in the glass at that point. When there is more than a dull light showing at the connector point, the termination was not successful. The light should also pass through the fusion splice, if it does not, stop and re- splice or re-terminate.
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