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ByVivek Kumar Sharma

1RV13EE059

Introduction Optical Fiber Communication Principle of Operation Optical Fiber Networking Applications Fiber Space Optic

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The light-guiding principle behind optical fibers was first demonstrated by Daniel Colladon and Jaques Babinet

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.

Optical fibers are long, thin strands of very pure glass usually 120 µm in diameter. They are arranged in bundles called optical cables and used to transmit light signals over long distances.

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Propagation of light wave through Optical fiberAny light wave which travels along the core and meets the

cladding at the critical angle of incidence will be totally

internally reflected. Therefore light wave is propagated along

the fiber core by a series of total internal reflections.

Acceptance Angle Meridional ray A enters the fiber core at an angle θa.

Incident ray b at an angle greater than θa is refracted into the cladding an eventually lost by radiation.

An acceptance angle defined by the conical half angle θa. θa is the maximum angle to the axis at which light may enter the fiber in order to be propagated is called acceptance angle for the fiber.

Numerical Aperture (NA)Numerical aperture of the fiber is the light collecting efficiency of

the fiber and is the measure of the amount of light rays that can be

accepted by the fiber. It is equal to the sine of acceptance.

NA = n0 sin θa = (n12 – n2

2)1/2

where, n1 and n2 are the refractive indices of core and

cladding respectively.

Numerical aperture of step index fiber is given as

NA = n1 √2∆

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Fiber Core Fiber Cladding

The core of a conventional optical fiber is a cylinder of glass or plastic that runs along the fiber's length. The core is surrounded by a medium with a lower index of refraction, typically a cladding of a different glass, or plastic

Cladding is one or more layers of materials of lower refractive index, in intimate contact with a core material of higher refractive index. The cladding causes light to be confined to the core of the fiber by total internal reflection at the boundary between the two.

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In practical fibers, the cladding is usually coated with a tough resin buffer layer

Buffer layer 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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Types

Fiber TypesClassification on the basis of the refractive index of the material

Step index fiber

Refractive index of core is uniform throughout and

undergoes an abrupt change at the core cladding

boundary.

In the graded index fiber, the refractive index of the core is made to vary in the parabolic manner such that the maximum value of refractive index is at the center of the core.

Based on the modes propagating in optical fiber: Single mode fiber Multi mode fiber

Single mode fiberSingle mode fiber optic cable has a small diametric core that allows only one mode of light to propagate.

Multi mode fiberMultimode fiber optic cable has a large diametric core that allows multiple modes of light to propagate

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Comparison Single mode fiber Multi mode fiber

► Core radius is small.

► Supports one mode of propagation.

► Optical source- LASER.

► The launching of optical power into

fiber is difficult as the core radius is

small.

► Supports larger bandwidth.

► Intermodal dispersion is absent.

► Used for long distance

communication.

► Core radius is large.

► Supports hundreds of modes.

► Optical source- LED.

► The launching of optical power into

fiber is easier as the core radius is

large.

► Supports lesser bandwidth.

► These fiber suffer from Intermodal

dispersion.

► Used for short distance

communication.

Networking

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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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Splicing is the method to connect one fiber optic cable to another permanently. Splices are "permanent" connections between two fibers.

It is the attribute of permanence that distinguishes a splice from connectors.

Splicing is only needed if the cable runs are too long for one straight pull or you need to mix a number of different types of cables.

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An optical network unit (ONU) is a device that transforms incoming optical signals into electronics at a customer's premises in order to provide telecommunications services over an optical fiber network.

ONU provides the subscribers with broadband Internet access.

It is used in combination with an optical line terminal (OLT).

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Fiber optic couplers are used to split the input signals into two or more outputs; they are called splitters in this case. 

On the other hand, some types of couplers can be used to combine two or more inputs into one single output; they are called combiners in this case.

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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

This allows long distances to be spanned with few repeaters.

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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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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

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FSO was initially developed by NASA and US Military.

FSO is a line of sight technology which uses LASERS and photo-detectors to provide optical connection between two point without using optical fibers.

Uses invisible beam of light to provide optical bandwidth connections.

FSO can transmit video ,data etc. at high speed capable of reaching a speed of 1.25Gbps

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It's based on connectivity between FSO-based optical wireless units.

Provide full-duplex (bi-directional) capability.

Each optical wireless unit uses an optical source, plus a lens or telescope.

Receiving lens or telescope connects to a high-sensitivity receiver via optical fiber.

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Advantages Disadvantages

Ultra High Bandwidth Small size & weight Electrical Isolation Immune to electrical

Interference Signal security Low transmission loss Ruggedness , flexibility Point to Point

Communication

High maintenance cost

Expensive optical transmitter & receiver

Prone to corrosion Difficult to splice

compare to wires High optical power

may result in fiber fuse

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