What is Optical fiber ?

An optical fiber (or optical fibre) is a flexible, transparent fiber made of high quality extruded glass (silica) or plastic, slightly thicker than a human hair. It can function as a waveguide, or “light pipe”, to transmit light between the two ends of the fiber.

1. FIBRE OPTICS
Mahabahu
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2. Contents
·1.Introduction
o2 Optical fiber communication
·3 Principle of operation
o3.1 Multimode fiber
o3.2 Singlemode fiber
o3.3 Special-purpose fiber
o3.4 Materials
o3.5 Fiber fuse
·4 Manufacturing
·5 Optical fiber cables
·6 Termination and splicing
·7 Application
·8 Conclusion
·9 References
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3. 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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4. 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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5. Principle of operation
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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.

6. 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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7. 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.

8. 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

9. 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.

10. 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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11. 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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12. 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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13. 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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14. 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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15. 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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16. 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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17. Optical fiber cables
For 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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18. Optical fiber cables
For 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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19. 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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20. 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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21. Applications
Fiber 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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22. Applications
Fiber 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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23. 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

24. 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

25. 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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