EoW May 2013

Technical article

jacket. At the same time, the jacket must be about one-third the size of conventional jackets. The free space around the glass needed to be reduced to make the cable as small as possible. Yet, the cable had to meet all impact, resistance and crush strength testing. As small form factor cables are handled, the fibre can actually migrate to one side or the other of the jacket as the loose yarns give way. Once that occurs, the fibre is less protected on one axis and no longer provides the protection that was conceptually designed into it. By using a tape with an adhesive matrix material, a custom tooling was designed to wrap several times around the fibre in a longitudinal fashion. The longitudinal tape wrapping ensures the centring of the fibre while only a very thin outer jacket bonds to the tape. This bonding allows installers to perform reasonable hand pulling or hand setting of the cable without stretching the jacket. By enabling the tape and jacket to bond as a single entity, the fibre cable could be handled much like a piece of copper wire in terms of strength. While many micro-cables are available today, they typically use Aramid yarns intertwined around the fibre. None have actually coupled the yarns, jacket and fibre together. This cable is unique because it uses an Aramid tape instead of loose yarns. The tape can also be stripped using conventional copper cable stripping machines or copper wire stripping machines. Lineman’s scissors can even be used to strip these cables – the first time this has been achievable with a coated fibre without requiring a specialised tool. It should also be noted that RBR fibre, rapidly becoming the standard in FTTX solutions and central offices/data centres, also adds to the handling qualities of these new fibres. Smaller cables can be bent around tighter configurations to fit various types of modules and installations. 4 Connectorisation The bonding of the tape and jacket, however, created a new challenge with connectorisation. Bonding the two together eliminated the space required for the fibre to “push back” from the connector. Therefore, connectors had to be re-designed specifically for use with these new fibres. These new connectors take into account that the fibre has no push back, or compression capability, within the jacket.

1.2mm optical ‘wire’ after release of pulling tension. Note: No deformation

Minimum normal grip to lift 5lb

1.2mm optical ‘wire’

5lb (2.25kg) load

▲ ▲ Figure 4 : Experimental fixture to simulate 5lb (2.25kg) hand pull on 1.2mm patch cord

24-fibre bundle, 2.0 diameter cable

24-fibre bundle, 1.2 diameter cable

▲ ▲ Figure 5 : Size comparison of 1.2mm and 2.0mm bundled cable

that could meet the requirements for more density while providing wire-like strength that would allow it to be handled and pulled without causing attenuation and other performance issues. The challenges were met by solving three major issues – strength, connectivity and thermal balancing. 3 Achieving copper- like strength To provide the strength of copper in a 1.6mm fibre optic cable was the first challenge. Installers should be able to pull the cable in a straight line like copper wire without needing to wrap it around a mandrel to keep from damaging the

As optical cable sizes were reduced to 1.6mm, this phenomenon was caused by as little as a few ounces of force instead of pounds. Thus, as optical cables became smaller, more delicate handling was required during installations. This new category of cables became known as “small form factor” cables because they could no longer pass the same testing as their larger counterparts. Tensile gradings went from 22 pounds to nine pounds, allowing minimal amounts of Aramid yarn and decreased jacket thickness. But it also resulted in products that required much more care in handling than any copper wire. The challenge was to develop a new fibre cable design for small form factor products

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May 2013