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Introduction to Optical Fibre Cable
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TRANSMITTER
INFORMATION
CHANNEL
(MEDIUM)
RECEIVER
Basic Communication System
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In optical communication transmission in anoptical format is carried out by varying theintensity of the optical power. (Intensity
modulation)
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FibreDriver Source DetectorRegen.
Transmitter Receiver
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Optical fiber is a new medium, in whichinformation (voice, data or video) istransmitted through a glass or plastic fiber, inthe form of light
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Transmitter convert electrical signal to opticalsignals which is transmitted through fibre
Electronic interfaces
Electronic processing circuits
Drive circuitry Light source – LED/Laser
Optical interface
Output sensing and stabilization
Temperature sensing and control
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Receiver- receives the optical signals from thefibre and convert the same to its electricalequivalent
Detector [PIN photodiode/APD (Avalanchephotodiode)]
Detector used in fibre optical communications aresemiconductor photodiodes or photo-detectorswhich converts the received optical signal intoelectrical form
Amplifier Decision circuits
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Information Transmission Sequence
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Consists of Core and Cladding Core and Cladding are made up of same
material
The material used is optically transparent
Silica or borosilicate glass will be the usualmaterial
The R.I of the core will be slightly higher thanthe R.I of the cladding
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The core and cladding dia in mm
140100
12562.5
12550
1258
Cladding ( m)Core ( m)
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Optical Fibres are non conductive (Dielectric)
–Grounding and surge suppression notrequired
- Cables can be all dielectric
Electromagnetic immunity – Immune to electromagnetic interference
(EMI)
–No radiated energy
–Unauthorized tapping difficult
Advantages of Fiber Optics
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Large Bandwidth (> 50 GHz for 1 km length)
– Future upgradability
– Maximum utilization of cable right of way
–One time cable installation costs
Continued
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Low Loss (5 dB/km to < 0.25 dB/km typical)
–Loss is low and same at all operatingspeeds within the fiber's specified ban
–Long, unrepeated links (> 70 km is
operation) – Inexpensive light sources available
–Repeater spacing increases along withoperating speeds because low loss fibers
are used at high data rates
Continued
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Small, light weight cables.
–Easy installation and handling
–Efficient use of space
Available in Long lengths (> 12 kms)
–
Less splice points Security
–Extremely difficult to tap a fiber as it does
not radiate energy that can be received by
a nearby antenna –Highly secure transmission medium
Continued
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Security
–
Being a dielectric – It cannot cause fire –Does not attract lightning – It does not carry electricity –
Can be run through hazardous areas Universal medium –Serve all communication needs –Non –obsolescence
Continued
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Rarer to Denser medium
- Refracted rays move towards the normal
Denser to Rarer medium
- Refracted rays move away from normal
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Critical angle:- The angle of incidence in thedenser medium for which the angle of refractionis 90
When the angle of incidence is greater than the
critical angle, Total Internal Reflection occurs Refractive Index of core is 1.48
Refractive Index of cladding is 1.46
Contd..
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Total Internal Reflection
n1
n2
n1
n2
n1
n2
Angle of incidence
Angle of Refraction
Light is bent away from theNormal
Light does not enter secondmaterial
Light is reflected in the samematerial
Angle of incidence Angle of reflectionCritical angle
(Note:- n1 is greater than n2)
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The optical fibers can be classified inthree ways:
-Material- Size (or Mode)
- Refractive Index
O F Classification
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Wavelength Frequency Window Attenuation
Dispersion Bandwidth Numerical Aperture
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Sources of Loss in Fibers :The losses occurring in
fibers can be attributed to three main causes
1. Absorption
2. Scattering
3. Geometric effects
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Permanent connection between two fibres
Involves cutting of the edges of the two fibres tobe spliced
Alignment of the cores of the fibres to beconnected is important to reduce splice loss
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Single Fiber Mechanical splicing Adhesive bonding or Glue splicing Temp. Mechanical splicing Fusion Splicing
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Most popular splicing technique Achieved either through electrical arc or throughgas flame
Splicing loss can be minimized as low as 0.01dB/joint
Splice joint needs mechanical protection andprotection from moisture. For this epoxy resincoating and heat shrinkable tube are used
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Suitable for SMF for use in long haul network The splice loss indicated by the splicing machine
is only an estimated loss.
After every splicing is over, the splice lossmeasurement is to be taken by an OTDR
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