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OPTICAL FIBER COMMUNICATIONS

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Optical Fibres

Sheath 1

Sheath 2Sheath 3

Aluminum Tape

Strength Member

Steal Wire Reinforcement

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IntroductionOptical Fiber It is a glass filament or wire which carries

light. It is a cylindrical waveguide that operate at

optical frequency. It confines electromagnetic energy in the form

of light.

●COMMUNICATION It may be broadly defined as the transfer of

information from one point to another.

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Light is the form of electromagnetic Wave just as radio waves, but with high frequency and shorter wavelength.

Spectrum Frequency Wavelength

Radio waves 100 KHZ to1 THZ 3KM to 300 µm

Infra Red light 1 THZ to 100 THZ 300 to 3 µm

Optical Communication

176 THz to 375 THZ

1.7 to 0.8 µm

1550 nm Window 193.5 THz 1.550 µm

1310 nm Window 230 THz 1.310 µm

850 nm Window 353 THz 0.85 µm

Visible Light 428 to 750 THZ 0.7 TO 0.4 µm

UV,X & γ rays 750 to 10 7 THZ 0.4 to 3x10 - 6 µm

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0 102 104 106 108 1010 1012 1014 1016 1018 1020 1022

Long wave

Standard

broadcast VHF

UHFShort wave

Radiofrequencies

Microwave

Millimeter

Wave

Far infrared

infrared

Ultraviolet

X-Rays

Gamma Rays

Cosmic rays

Red

~0.7 µm

Violet

~0.4 µm

1.7 µm 0.8 µm

Optical Fibre Communication

Frequency (Hz)

Wavelength3000 km 30 km 300 m 3 m 3 cm 0.3 mm 3 µm 30 nm 0.3 nm 3 pm 0.3 pm

f = 1/T λ = c/f c = 3x108 m/s

f = 100 Hz λ = 3x108 m f = 1 GHz λ = 0.3 m

f = 100 KHz λ = 3x103 m f = 1 THz λ = 300 µm

f = 100 MHz λ = 3 m f = 200 THz λ = 1.5 µm

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HISTORYHollow Logs, Drum (different sizes), Wind Instruments

(pipes), Smoke Signals, Signal fires and Signaling lamps.

The first optical fiber exhibited very high attenuation i.e. 1000 dB/Km. While coaxial cable losses were 5-10 dB/Km.

Fiber losses were reduced to below 5 dB/Km.Development of fiber waveguides with optical

frequencies at small wavelengths requires the development of all optical components.

Laser Life at the start was 1000 Hrs & now is 100 years.

At present two optical windows are in operation i.e. 1310 nm ,1550nm.

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Advantages of Optical FiberEnormous potential bandwidth The maximum capacity of single mode step index fiber is

1.6 Tb/Sec w.r.t coaxial cable bandwidth of 500 MHZ.Small size and weight

Optical fibers have very small diameter i.e. 125um which is just like a human hair while the dia of one copper is 0.8mm.The ratio of weight as compared to other cables is 25:1.

Electrical isolationOptical fibers are fabricated from glass which are electrical insulated hence they don't exhibit interference problem.

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Advantages of Optical FiberImmunity to Interference & Cross talk

The material of optical fiber is dielectric/glass hence there is no possibility of cross talk or leakage.

Signal SecurityThe light from optical fibers doesn't radiate significantly and therefore they provide a high degree of signal security.

Low transmission lossLaser light travels with high speed on pure transparent glass. This development of optical fiber over the last twenty years has resulted in the production of O/F cables with very low attenuation i.e. 0.2 dB/Km.

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Advantages of Optical FiberRuggedness & Flexibility

Cable structures have been developed which have proved flexible, compact & extremely high.

System Reliability & Ease of MtceDue to low transmission loss, intermediate repeaters & line amplifiers are reduced. Hence with few repeaters system reliability is generally enhanced. The optical component life time is 20 to 30 years.

Potential Low CostThe glass which generally provides the optical fiber transmission medium is made from sand which is available in abundance.

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Disadvantages of Optical FiberVery small hole on the surface of fiber may

weakens the tensile strength.A small bend on optical fiber causes radiation loss.Alignment problem, connectors & core

misalignment.The cost of fusion splicing is high.The fault localization is some what difficult.Clean environment is required during splicing. A

small dust particle can create high attenuation.