FIBRE OPTICS

Mahabahu

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Contents

1.Introductiono 2 Optical fiber communication 3 Principle of operation o 3.1 Multimode fiber o 3.2 Singlemode fiber o 3.3 Special-purpose fiber o 3.4 Materials o 3.5 Fiber fuse 4 Manufacturing 5 Optical fiber cables 6 Termination and splicing 7 Application 8 Conclusion 9 References

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Introduction• The light-guiding principle behind optical fibers was first

demonstrated in by Daniel Colladon and Jaques Babinet in the 1840s, with Irish inventor John Tyndall offering public displays using water-fountains .

• An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length by confining as much light as possible in a propagating form.

• Optical fibers are widely used in fiber-optic communication, which permits transmission over longer distances and at higher data rates than other forms of wired and wireless communications.

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FOR MORE INFO...

Optical fibrecommunication

• Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables.

• It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables.

• This allows long distances to be spanned with few repeaters.

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Principle of operation04/11/23

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Fiber-optic transmission of light depends on preventing light from escaping from the fiber.

When a beam of light encounters a boundary between two transparent substances, some of the light is normally reflected, while the rest passes into the new substance.

A principle called total internal reflection allows optical fibers to retain the light they carry.

When light passes from a dense substance into a less dense substance, there is an angle, called the critical angle, beyond which 100 percent of the light is reflected from the surface between substances.

Principle of operation• Total internal reflection occurs when light

strikes the boundary between substances at an angle greater than the critical angle.

• An optical-fiber core is clad (coated) by a lower density glass layer. Light traveling inside the core of an optical fiber strikes the outside surface at an angle of incidence greater than the critical angle so that all the light is reflected toward the inside of the fiber without loss.

• As long as the fiber is not curved too sharply, light traveling inside cannot strike the outer surface at less than the critical angle. Thus, light can be transmitted over long distances by being reflected inward thousands of times with no loss

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Multimode fiber • Fiber with large (greater than 10 μm) core

diameter may be analyzed by geometric optics

• Such fiber is called multimode fiber,

• In a step-index multimode fiber, rays of light are guided along the fiber core by total internal reflection.

• Rays that meet the core-cladding boundary at a high angle boundary, are completely reflected.

• Rays that meet the boundary at a low angle are refracted from the core into the cladding,

• and do not convey light and hence information along the fiber.

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The propagation of light through a multi-mode optical fiber.

Singlemode fiber• Fiber with a core diameter less than

about ten times the wavelength of the propagating light cannot be modeled using geometric optics.

• Instead, it must be analyzed as an electromagnetic structure, by solution of Maxwell's equations as reduced to the electromagnetic wave equation.

• As an optical waveguide, the fiber supports one or more confined transverse modes by which light can propagate along the fiber.

• Fiber supporting only one mode is called single-mode or mono-mode fiber.

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A typical single-mode optical fiber, showing diameters of the component layers

Special-purpose fiber • Some special-purpose optical fiber is constructed with a non-

cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section.

• These include polarization-maintaining fiber and fiber designed to suppress whispering gallery mode propagation.

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Materials

Glass optical fibers are almost always made from silica

Plastic optical fiber (POF) is commonly step-index multimode fiber

POF typically has much higher attenuation than glass fiber 1 dB/m or higher, and this high attenuation limits the range of POF-based systems.

Fiber fuse

• At high optical intensities, above 2 megawatts per square centimetre

• when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur

• The open fiber control system, which ensures laser eye safety in the event of a broken fiber

• can also effectively halt propagation of the fiber fuse

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Fiber fuse

undersea cables

• where high power levels might be used without the need for open fiber control

• A "fiber fuse" protection device at the transmitter can break the circuit to prevent any damage

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Manufacturing

• Standard optical fibers are made by first constructing a large-diameter preform

• with a carefully controlled refractive index profile

• and then pulling the preform to form the long, thin optical fiber

• The preform is commonly made by three chemical vapor deposition methods: inside vapor deposition, outside vapor deposition, and vapor axial deposition.

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Manufacturing

• With inside vapor deposition • a hollow glass tube approximately 40 cm in

length known as a "preform" is placed horizontally and rotated slowly on a lathe

• and gases such as silicon tetrachloride (SiCl4) or germanium tetrachloride (GeCl4) are injected with oxygen in the end of the tube

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Manufacturing• The gases are then heated by means of an external hydrogen

burner

• bringing the temperature of the gas up to 1900 Kelvin

• where the tetrachlorides react with oxygen to produce silica or germania (germanium oxide) particles

• When the reaction conditions are chosen to allow this reaction to occur in the gas phase throughout the tube volume

• in contrast to earlier techniques where the reaction occurred only on the glass surface, this technique is called modified chemical vapor deposition.

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Manufacturing

▫ The oxide particles then agglomerate to form large particle chains

▫ which subsequently deposit on the walls of the tube as soot.

▫ The deposition is due to the large difference in temperature between the gas core and the wall causing the gas to push the particles outwards (this is known as thermophoresis

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Optical fiber cables • In practical fibers, 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 fiber but do not contribute to its optical wave guide properties.

• Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers,

• To prevent light that leaks out of one fiber from entering another.

• This reduces cross-talk between the fibers

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Optical fiber cablesFor indoor applications• The jacketed fiber enclosed, with a bundle of

flexible fibrous polymer strength members like Aramid or (Kevlar)

• In a lightweight plastic cover to form a simple cable.

• Cable terminated with a specialized optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment.

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Optical fiber cablesFor use in more strenuous environments

• A much more robust cable construction is required

• In loose-tube construction the fiber is laid helically into semi-rigid tubes

• Allowing the cable to stretch without stretching the fiber itself

• This protects the fiber from tension during laying and due to temperature changes

• Alternatively the fiber may be embedded in a heavy polymer jacket, commonly called "tight buffer" construction

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Termination and splicing

• Optical fibers are connected to terminal equipment by optical fiber connectors

• Optical fibers may be connected to each other by connectors or by splicing

• that is, joining two fibers together to form a continuous optical waveguide

• For quicker fastening jobs, a "mechanical splice" is used

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Applications

Optical fiber communication

• Optical fiber can be used as a medium for telecommunication and networking

• because it is flexible and can be bundled as cables.

• It is especially advantageous for long-distance communications,

• because light propagates through the fiber with little attenuation compared to electrical cables.

• This allows long distances to be spanned with few repeaters.

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ApplicationsFiber optic sensors

• Optical fibers can be used as sensors to measure strain, temperature, pressure and other parameters.

• The small size and the fact that no electrical power is needed at the remote location gives the fiber optic sensor advantages to conventional electrical sensor in certain applications.

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ApplicationsFiber optic sensors

• Optical fibers are used as hydrophones for seismic or SONAR applications.

• Hydrophone systems with more than 100 sensors per fiber cable have been developed.

• Hydrophone sensor systems are used by the oil industry as well as a few countries' navies.

• Both bottom mounted hydrophone arrays and towed streamer systems are in use.

• The German company Sennheiser developed a microphone working with a laser and optical fibers

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Applications Other uses of optical fibers

• Fibers are widely used in illumination applications.

• They are used as light guides in medical and other applications In some buildings

• optical fibers are used to route sunlight from the roof to other parts of the building

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A frisbee illuminated by fiber optics

Applications•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

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A fiber-optic Christmas Tree

conclusion• Fiberoptics, a branch of optics dealing with the transmission of

light through hair-thin, transparent fibers.

• A principle called total internal reflection allows optical fibers to retain the light they carry.

• The development of new optical techniques will expand the capability of fiber-optic systems.

• Newly developed optical fiber amplifiers, for example, can directly amplify optical signals without first converting them to an electrical signal, speeding up transmission and lowering power requirements.

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