Fibre Optic Cable
A package for an optical fibre or fibres that may include cladding, buffering, strength members and an outer jacket.
Fibre optic cable functions as a light guide, guiding the light introduced at one end of the cable through to the other end.
Singlemode cable is a single strand of glass fibre with a diameter of 8.3 to 10 microns, has one mode in which light will propagate, 1310 or 1550nm. Singlemode fibre carries higher bandwidth than multimode fibre but requires a light source with a narrow spectral width. The small core and single light wave virtually eliminate any distortion that could result from overlapping light pulses providing the least signal attenuation and the highest transmission speeds of any fibre cable type.
Typical multimode fibre core diameters are 50, 62.5, and 100 micrometres. Multimode fibre gives high bandwidth at high speeds over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable’s core typically 850 or 1300nm. However, in long cable runs multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission.
The cladding is usually coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually plastic. These layers add strength to the fibre but do not contribute to its optical waveguide properties. Rigid fibre assemblies sometimes put light absorbing glass between the fibres, to prevent light that leaks out of one fibre from entering another. This reduces cross-talk between the fibres or reduces flare in fibre bundle imaging applications. For indoor applications, the jacketed fibre is generally enclosed, with a bundle of flexible fibrous polymer strength members like Aramid (e.g. Twaron or Kevlar), in a lightweight plastic cover to form a simple cable.
Each end of the cable may be terminated with a specialized optical fibre connector to allow it to be easily connected and disconnected from transmitting and receiving equipment. For use in more strenuous environments, a much more robust cable construction is required. In loose-tube construction, the fibre is laid helically into semi-rigid tubes, allowing the cable to stretch without stretching the fibre itself. This protects the fibre from tension during laying and due to temperature changes. Alternatively, the fibre may be embedded in a heavy polymer jacket, commonly called tight buffer construction. These fibre units are commonly bundled with additional steel strength members, again with a helical twist to allow for stretching. The cable may also be armoured to protect it from environmental hazards, such as construction work or gnawing animals. Undersea cables are more heavily armoured in their near-shore portions to protect them from boat anchors, fishing gear, and even sharks, which may be attracted to the electrical power signals that are carried to power amplifiers or repeaters in the cable. Modern fibre cables can contain up to a thousand fibres in a single cable, so the performance of optical networks easily accommodates even today’s demands for bandwidth on a point to point basis.
POF is a plastic-based cable which promises performance similar to glass cable on very short runs but at a lower cost. Plastic core cable is used for short distance applications.
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