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Optical Fibre Cables

9/6/2013 3:21:38 PM | by The Green Book

Optical Fibre Cables


Optical fibre cables are cables that contain optical fibres and they are used to transmit digital information in the form of light pulses over great distances at extremely high speeds. They are becoming increasingly popular and have many uses, ranging from medical imaging to telecommunications.


Optical fibres are very fine strands of optical glass that are slightly thicker than a strand of human hair. An optical fibre is made up of a core, which is the pure optical glass. Around the core is a cladding, which is made of an optical material that reflects light back into the core. A buffer coating then protects the fibre from damage. Optical fibre cables are made up of hundreds or thousands of these fibres bundled together in a jacket, which is the outer covering of the cable. Sometimes, light-absorbing glass is placed between the fibres to capture any light that leaks from the fibres, reducing flare in the final image produced.


The protective covering on the cable depends on the situation it will be used in. For cables that are used in more robust conditions, such as underwater, precautions such as placing the cable in loose tubes that allow it to bend without the cable itself bending and filling the tube with gel or dry block are taken. Other precautions such as Kevlar wrappings are also used.


There are two kinds of optical fibres – single-mode and multi-mode. Single mode fibres have smaller cores compared to multi-mode fibres and transmit infrared laser light rather than infrared light.


Optical fibres work on the principle of total internal reflection, where the angle that the light enters the fibre and hits the surface of the fibre at causes the light ray to be reflected back into the fibre at that same angle. This is also because the cladding is an optically less dense material as compared to the glass. Thus, the ray of light is reflected through the fibre and it can travel great distances since none of the light ray is lost. However, some degradation of the light does occur, due to impurities in the optical glass.


The light can be produced by lasers or LEDs (light-emitting diodes) and after it has traveled through the optical fibre, it is received by the optical receiver, which decodes the light pulses and changes them to electrical signals, which are then sent to devices such as televisions or telephones.


Optical fibre cables are being used in many industries nowadays, particularly telecommunications. This is because compared to the old copper wires that were used, optical fibre cables have much more advantages.


Optical fibre cables are much more efficient compared to copper wires. They are much cheaper to produce and since they are thinner, more fibre optics can be placed in a cable, allowing more signals to be sent. Fewer signals are lost when fibre optics are used compared to copper and the signal is also clearer, since the light signals do not interfere with each other like electrical signals. Since fewer signals are lost, a lower power transmitter can be used, thus saving more money.


They are also less hazardous as there is no risk of fire, unlike electrical signals. They are also lighter and take up less space. They are more flexible than electrical cables, which has allowed their use in digital cameras that are used in medical and mechanical imaging.


However, optical fibres cables do have their disadvantages as well. Although they are initially very strong, there are unavoidable microscopic flaws, both in the manufacturing process and the handling of the cable as it is installed. The strength of the optical fibre cable will be reduced over time, depending on the conditions it is installed in.


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