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ABC for working with Fibre Optics for beginners

Introduction on working with optical fibres.


The transition from copper to fibre-optic technology means the need for new tools and skills. Aside from acquiring some theoretical knowledge, installers must improve their manual skills as the work with optical fibres requires a different, more careful approach.
Similarly to other types of cable systems, the process of installation of a fibre optic system can be divided into three main stages:

  • laying cables
  • installing connectors and passive components
  • installing and configuring active devices

The way of laying cables is essential for attenuation of the transmitted optical signals. Each cable contains one or more fibres. The fibre type determines the minimum bending radius, however the installer should not confuse the minimum bending radius of a single fibre and of the cable itself.
The minimum bending radius of a cable is usually equal to 20x its diameter. The minimum bending radius of a single fibre depends on its standard, e.g.:

  • 30 mm for G.652D fibres
  • 10 mm for G.657A1 fibres
  • 7.5 mm for G.657A2 fibres

In the case of FTTH (Fibre To The Home) systems, the recommended standard is the G.657A2, with the smallest minimum bending radius. This greatly facilitates the work of the installer and minimizes problems associated with the increase of signal attenuation caused by sharp bends (right angles etc).
During installation of cables it is not allowed to exceed maximum pulling force. Unlike in the case of coaxial or twisted pair cables, the fault location in a fibre is not easy unless the installer has an expensive device - reflectometer.
The connection and configuration of active optical devices is not difficult, in general the procedures are similar to those having place in LAN networks based on UTP cabling. However, the installer should remember about two important issues:


1. IR laser light is invisible to the human eye, but can be very harmful - all connections should be done before any devices are powered on.
2. Optical devices and connectors require high standards of cleanliness - any dirt will increase the attenuation of the optical link.


Most problems experienced by novice installers are encountered during connecting optical fibres. Here are several practical tips that are common for all splicing techniques (fusion splicing, mechanical splicing, gluing and polishing). We hope they will help some people start the adventure with fibre optic technology.

1. Fibre cable reserve and free fibres

It may be part of the installer to think ahead and inform the investor/customer that some spare cable lengths and several additional fibres in each cable can solve many problems in the future.
One point-to-point link requires two fibres, or with the use of WDM technology - a single fibre. When, for example, one needs four fibres, it is reasonable to use an 8-fibre cable than the "minimum" four-fibre one (popular optical cables usually have 2, 4, 8, 16, 24 ... fibres). Fibre optic cables are cheap, but the re-installation cost can be high and should be avoided, so it is much better to have spare fibres for the future needs or simply as a backup in the case of a failure of one fibre.

 

Fibre cable reserve left by the cable input to the building. The additional length of the cable is stored on a spare cable storage rack mounted on a wall.


It is highly recommended to leave an additional length of the cable on a spare cable storage rack - usually about 10 meters or so. The additional attenuation is negligible in comparison with that caused by splices and connections. In the future, the reserve of the cable can solve problems caused by unexpected situations (new location of a server, a need to change the cable path etc). Having a cable reserve, the installer can make changes without additional costs that would be necessary in the case of laying new cable.

 

 

2. Distribution frames and boxes

As mentioned earlier, cables and fibres feature respective minimum bending radii. The easiest and fastest solution for securing cable/fibre interconnections and terminations is to use suitable distribution frames and boxes with trays for the cables and fibres. They force correct positioning of the cables and fibres and prevent accidental damages to the fibres at the interconnections and terminations.