Post on 06-Apr-2018
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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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Continued
In optical communication transmission in an
optical format is carried out by varying the
intensity of the optical power. (Intensity
modulation)
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Basic FibreOptic Link
FibreDriver Source DetectorRegen.
Transmitter Receiver
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Fibre Optics
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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Basic Elements of Transmitters
Transmitter convert electrical signal to optical signals
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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Basic elements of an Optical Receiver
Receiver- receives the optical signals from the fibre
and convert the same to its electrical equivalent
Detector [PIN photodiode/APD (Avalanche
photodiode)]
Detector used in fibre optical communications are
semiconductor photodiodes or photo-detectors
which converts the received optical signal into
electrical form
Amplifier
Decision circuits
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Information Transmission Sequence
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Fiber Construction
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 usual material
The R.I of the core will be slightly higher than the
R.I of the cladding
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Contd
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 not required
- 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 antennaHighly secure transmission medium
Continued
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Security
Being a dielectric It cannot cause fireDoes not attract lightning It does not carry electricity
Can be run through hazardous areas Universal mediumServe all communication needsNonobsolescence
Continued
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Light Propagation Through O.F
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 the densermedium for which the angle of refraction is 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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Total Internal Reflection
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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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Optical Fiber Parameters
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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Splice
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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Splicing Methods
Single Fiber Mechanical splicing
Adhesive bonding or Glue splicing
Temp. Mechanical splicing
Fusion Splicing
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Fusion Splicing
Most popular splicing technique Achieved either through electrical arc or
through gas flame Splicing loss can be minimized as low as 0.01
dB/joint Splice joint needs mechanical protection and
protection from moisture. For this epoxyresin coating and heat shrinkable tube are
used
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Fusion Splicing Contd
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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