Optical Fiber: Definition, Properties and Uses

What is Optical Fiber?
An optical fiber or optical fibre is a thin, flexible, transparent fiber that acts as a waveguide, or “light pipe”, to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

optical fiber
Figure: Optical fiber

An optical fiber is composed of a light-transmitting, transparent core material coated with a material with lower refractive index. Silica glass is the most common material for optical fibers. Optical fibers are of small size and lightweight, compatible with textile yarns, and readily embedded or even woven inside TSCs, they are the most promising medium to form the sensing network.

They are classified into three groups according to the types of core material, quartz, multi-component and plastic optical fibers (POF).

Normally, an optical fiber consists of a core surrounded by a cladding whose refractive index is slightly smaller than that of the core. The optic fiber is coated during the fiber drawing process with a protective layer of polymer.

The quartz optical fiber is used for long-distance optical communication including public trunk lines because its transmission loss is as low as 1 dB/km or under. The multi-component optical fiber is used for middle-distance communication of 1-2 km including local area networks (LAN) in plants and fiber scopes. The glass optical fiber has a shortcoming in that its processing requires great skill because it is expensive, brittle and hard to process. Meanwhile, the plastic optical fiber has advantages in that its inexpensive, flexible, light and easy to process, though the transmission loss is as high as 120–130 dB/km. It is, therefore, widely used for short distance wave guides including optical sensors, optical transmission in equipment, mobile optical communication and display.

Optical fibres are made of glass or plastic, and they have high optical clarity. Light travels internally through the fiber across long distances via reflection, and it retains its luminescence. Signals can be passed in either analogue or digital forms within a machine or from one machine to another.

Properties of Optical Fiber:

  1. Light-Emitting in varying colors
  2. Brittle which is why such fibers are encased in steel wire
  3. Washable

Uses of Optical Fiber:
Fibers are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line-of-sight path. In some buildings, optical fibers are used to route sunlight from the roof to other parts of the building. Optical fiber illumination is also used for decorative applications, including signs, art, and artificial Christmas trees. Swarovski boutiques use optical fibers to illuminate their crystal showcases from many different angles while only employing one light source. Optical fiber is an intrinsic part of the light-transmitting concrete building product, LiTraCon.

Optical fiber is also used in imaging optics. A coherent bundle of fibers 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 (endoscopy). Industrial endoscopes are used for inspecting anything hard to reach, such as jet engine interiors.

In spectroscopy, optical fiber bundles are used to transmit light from a spectrometer to a substance which 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 fibers, a spectrometer can be used to study objects that are too large to fit inside, or gasses, or reactions which occur in pressure vessels.

An optical fiber 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 fibers can be used to provide signal amplification by splicing a short section of doped fiber into a regular (undoped) optical fiber line. The doped fiber 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 fiber, which transfers energy from the second pump wavelength to the signal wave. The process that causes the amplification is stimulated emission.

Optical fibers doped with a wavelength shifter are used to collect scintillation light in physics experiments. Optical fiber can 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 highpowered antenna elements and measurement devices used in high voltage transmission equipment.

A growing trend in iron sights for arms, is the use of short pieces of optical fiber for contrast enhancement dots, made in such a way that ambient light falling on the length of the fiber is concentrated at the tip, making the dots slightly brighter than the surroundings. This method is most commonly used in front sights, but many makers offer sights that use fiber optics on front and rear sights. Fiber optic sights can now be found on handguns, rifles, and shotguns, both as aftermarket accessories and a growing number of factory guns.

Optical fibers are used in safety products such as vests and road signs. Dresses (Hussein Chalayan fibre-optic dress), shirts and health monitors, for example heart beat, body temperature, children susceptible to S.I.D’s. Uses also include soft furnishings, such as curtains, bed headboards and cushions. Other uses include umbrellas and flexible screens to display graphics and text used on jackets, rucksacks etc.


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