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Optical Fibre and its Applications

Optical Fibre and its Applications

OPTICAL FIBRE

  • An optical fibre is a flexible, transparent fibre made of glass (silica) or plastic, slightly thicker than a human hair. It functions as a waveguide to transmit light between the two ends of the fibre.
  • The field of applied science and engineering concerned with the design and application of optical fibres is known as fibre optics.
  • Optical fibres are widely used in fibre-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication.
  • Fibres are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference.
  • Fibres are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces. Specially-designed fibres are used for a variety of other applications, including sensors and fibre lasers.
  • Optical fibres typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fibre to act as a waveguide.
  • Fibres that support many propagation paths or transverse modes are called multi-mode fibres (MMF), while those that only support a single mode are called single-mode fibres (SMF).
  • Multi-mode fibres generally have a wider core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibres are used for most communication links longer than 1,050 meters.
  • Glass optical fibres are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses as well as crystalline materials like sapphire, are used for longer-wavelength infrared or other specialized applications.
  • Silica and fluoride glasses usually have refractive indices of about 1.5, but some materials such as the chalcogenides can have indices as high as 3. Typically the index difference between core and cladding is less than one percent.
  • Plastic optical fibres (POF) are commonly step-index multi-mode fibres with a core diameter of 0.5 millimetres or larger.
  • POF typically have higher attenuation coefficients than glass fibres, 1 dB/m or higher, and this high attenuation limits the range of POF­-based systems.

APPLICATIONS OF OPTICAL FIBRE

  • Optical fibre can be used as a medium for telecommunication and computer networking because it is flexible and can be bundled as cables.
  • It is especially advantageous for long-distance communications, because light propagates through the fibre with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters.
  • For short distance applications, such as a network in an office building, fibre-optic cabling can save space in cable ducts. This is because a single fibre can carry much more data than electrical cables such as standard category 5 Ethernet cabling.
  • Fibre is also immune to electrical interference; there is no cross-talk between signals in different cables, and no pickup of environmental noise.
  • Non-armoured fibre cables do not conduct electricity, which makes fibre a good solution for protecting communications equipment in high voltage environments, such as power generation facilities, or metal communication structures prone to lightning strikes. They can also be used in environments where explosive fumes are present, without danger of ignition.
  • Fibres have many uses in remote sensing. In some applications, the sensor is itself an optical fibre. In other cases, fibre is used to connect a non-fibre optic sensor to a measurement system.
  • Depending on the application, fibre may be used because of its small size, or the fact that no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fibre by using different wavelengths of light for each sensor, or by sensing the time delay as light passes along the fibre through each sensor.
  • Optical fibres can be used as sensors to measure strain, temperature, pressure and other quantities by modifying a fibre so that the property to measure modulates the intensity, phase, polarization, wavelength, or transit time of light in the fibre.
  • Sensors that vary the intensity of light are the simplest, since only a simple source and detector are required.
  • Fibres are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shown on a target without a clear line-of-sight path. In some buildings, optical fibres route sunlight from the roof to other parts of the building.
  • Optical fibre illumination is also used for decorative applications, including signs, art, toys and artificial Christmas trees. Swarovski boutiques use optical fibres to illuminate their crystal showcases from many different angles while only employing one light source.
  • Optical fibre is also used in imaging optics. A coherent bundle of fibres is used, sometimes along with lenses, for a long, thin imaging device called an endoscope, which is used to view objects through a small hole.
  • Medical endoscopes are used for minimally invasive exploratory or surgical procedures. Industrial endoscopes are used for inspecting anything hard to reach, such as jet engine interiors.
  • In spectroscopy, optical fibre bundles transmit light from a spectrometer to a substance that cannot be placed inside the spectrometer itself, in order to analyze its composition. A spectrometer analyzes substances by bouncing light off of and through them. By using fibres, a spectrometer can be used to study objects remotely.
  • An optical fibre doped with certain rare earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. Rare-earth doped optical fibres can be used to provide signal amplification by splicing a short section of doped fibre into a regular (undoped) optical fibre line.
  • The doped fibre is optically pumped with a second laser wavelength that is coupled into the line in addition to the signal wave. Both wavelengths of light are transmitted through the doped fibre, which transfers energy from the second pump wavelength to the signal wave. The process that causes the amplification is stimulated emission.
  • Optical fibre can also be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment. Examples of this are electronics in high-powered antenna elements and measurement devices used in high voltage transmission equipment.

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SCIENCE AND TECHNOLOGY

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