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Fiber Optic Cables

Cabelte produced the first optical cable (multimode) in Portugal, in 1983. The cable was supplied to “Instituto para Desenvolvimento das Comunicações (IDC)” for the trial connection between “IDC” and “Inesc -Instituto de Engenharia de Sistemas e Computadores”.

The first cables produced for commercialization, called “light guide cables”, were made of 50/125 multimode fibers, tight structure, and had 4 to 6 fibers, regular customers were the former “CTT/TLP”, today “PT Comunicações”.

The big increase occurred in the production of optical fibre cables at Cabelte takes place at the beginning of the 90s, with the construction of a new plant and with the introduction of “loose” technology..

Since then, optical fiber has become more and more important and today is one of the most important telecommunication channels, due to the characteristics of the fiber itself, particularly its low attenuation associated with an almost infinite bandwidth (single mode fibers), and to the development occurred in the optical transmission systems.

Today, optical fiber cables are part of all communication “backbones” in metropolitan and regional networks. The presence of “triple pay” services, interactive games, high definition television, telemedicine, among others, requiring a high bandwidth in the access network, foresee the gradual replacement of copper by fiber optics up to the subscriber.

GENERAL OUTLINE
An optical fiber cable is generally formed by a central core where the fibers are grouped and by several protective layers. The design and dimensioning of an optical fiber cable aims, namely, to isolate the fiber from mechanical strain and environment conditions to which cable may be subjected during installation, but also during its lifetime.

The optical fiber (core and sheath), responsible for optical signal propagation, is coated by a double layer called primary coating that allows the handling of fiber avoiding the risk of contamination. Then, fiber is insulated again with a secondary coating which may be stretched, known as “tight” or “semi tight” or, it can be relaxed – “loose” and, in this case, one or more fibers may be accommodated in a same coating/tube. Most of the cables of Cabelte range are “loose” technology, and each tube may accommodate 1 to 16 fibers. Tubes may be stranded in concentric layers producing cables of various compositions with a large number of fibers may reaching several hundreds.

One of the most important aspects in the design of an optical fiber cable is the calculation of fiber excess-length (designation of the excess length of fiber in relation to the length of the cable, it allows cable elongation up to a certain limit when it is subjected to tension load during, for instance, installation without fiber elongation. This aspect is particularly important in aerial cables, since they are permanently under strain. It is achieved on the extrusion and stranding of tubes, by conjugating and controlling various parameters, such as extrusion line speed, temperatures, tension when winding tubes, lay-length, among others.

Prevent the entry of water inside optical fiber cables and restrict its propagation are very important aspects in what concerns outdoor cables, since it is known the adverse effects that prolonged exposure to water may have in transmission characteristics. Until very recently, cable tightness was achieved through the use of jelly which should fill the blank interstices of optical core. More recently, the pressure to reduce costs of installation imposed the elimination of jelly around the tubes avoiding part of the cleaning prior to fusion splicing. Thus, traditional jelly has gradually been replaced by dry material, such as wires and waterblocking tapes that swell when exposed to moisture, blocking the passage of water inside cables.

In special applications, where cables may be permanently exposed to water, transversal tightness reinforcement is usually achieved by the longitudinal application of an aluminium polymer coated tape thermo-welded to the sheath

Cabelte offer a very wide range of optical fiber cables for indoor and outdoor installations, suitable for conventional methods of installation (traction or blowing).

The adoption of latest technology allows the design of cables having a large number of fibres, with optimized diameters and weight, and of easy handling.

The increasing use of dielectric cables with no metallic elements boosted the application of materials with good mechanical characteristics, such as aramid, giving cables a high tensile strength and low weight. As an example, self supported cables ADSS type, and glass fiber rods generally used in the centre of cable core, functioning as tensile strength member but also as a support for tubes assembly and “anti-buckling”. However, for certain applications, mechanical metallic protection is applied. Corrugated steel tape longitudinally applied is the most common.

PRODUCT RANGE

Cabelte range comprises:

- Cables for duct and directly buried installation
- Cables for aerial installation
- Cables OPGW - for power ground wire with optical fibers incorporated for high voltage aerial lines

For specific protections:

- Cables with ballistic protection
- Cables with non metallic protection against rodents
- Cables with improved fire behaviour

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