Fiber Optic Facts

The fibre optic cable market is growing rapidly, due to the increasing demand for fibre internet. Fibre optic cables transmit data more quickly, more reliably and over greater distances than copper-based cables. Fibre optic cables are made up of several hundred fine fibres, comprising a synthetic silica core infused with boron and germanium and a silica cladding with a lower refractive index. The purpose of the cladding layer is to maintain the optical signal within the core and to add some mechanical strength. Data is transmitted through fibres by shining light through the cable. The light travels as a guided mode, which can be considered for simplicity as bouncing off the walls of the core, known as total internal reflection. The data is transmitted in binary, with a flash of light representing a 1 and an equal period of darkness representing a 0. This allows the data to be transmitted at a rate of more than 120,000 miles per
second!

The installation phase of a fibre optic cable is the most important step towards reliable data transmission at high speed, care must be taken to ensure that the cable while installing is not bent stretched or deformed. If mishandling is done, the best case is that the fibre core will break and be faulty, however, the worst case is that the fibre optic core will be damaged and cause signal distortion, which results in intermittent faults.

The glass core in a fibre optic cable is very fragile, it is found to be slightly thicker than a human hair but made of glass. Single mode fibre uses a special type of glass that is extruded into a solid medium to protect it. Multimode fibre is made from glass but being thicker (at 50 µm compared to 9 µm), is more robust. Because of this, Single mode fibre is more sensitive to breakage than Multimode. The cladding and buffer around the cable core helps to prevent damage; however, if the core is stretched or bent beyond its limit, the core will break.

When the fibre optic is physically compromised, there are two outcomes. One case is that the two glass core pieces are not physically aligned and no laser light will propagate. This case is seen as the best scenario as the fault can be located and fixed. The second case is that the glass core will be partially aligned after the breakage and pass a partial signal. The network may or may not work due to the drop in laser power. Another strong possibility is that the glass core could be damaged instead of being broken. For single mode fibre, the glass core might only crack and cause imperfection in the medium, which would reduce signal propagation and cause reflection. Multimode fibre is more likely to be damaged by flexing and cause loss of power.

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