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Optical Fibre Communication
• Lecture delivered by Christie Alwis
• 2009 faculty of Applied Science for computer science , and physics special
students.
• University of Sabaragamuwa , Belihuloya.
• For more details on this lecture, please visit
www.christiealwis.com
Revolutions
How it's going to be affected to the human being?
2. Industrial Revolution
1. Agricultural
Revolution
3. Communication Revolution
a.) can talk with the use of
latest Technology @ any
where in the world, @ low
cost.
b.) can be accepted
knowledge @ anywhere in
the world. (e- Assessment)
EXPLOSIVE GROWTH OF INTERNET
WHAT IS COMMUNICATION
NETWORK
Local Area Node
Country A
Domestic Transport
Network (OF,
IG
International
Transport Network
IG
Country B
Both Domestic and International Transport will be on Optical
Fibers. And Switching Nodes will be on NGN.
Undersea
Optical Fiber
Networks
BASIC COMPONENTS OF
COMMUNICATION NETWORKS
• Following 8 major components can be identified
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Geographical Location & Terminal
Access Networks
Local Exchange
Domestic Transport Network
International Exchange
International Transport Network
Other Country International Exchange
Other Country Domestic Network (With the similar components
as above)
DEVELOPMENT OF ACCESS
NETWORK
• Access Network is developed to accommodate
integrated services such as Internet, IPTV, Data with
TV
Voice
Power
Telephone
• Radio Options: 3G, EvDO, WiMAX
• xDSL, PON, and PLC
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FTTH, PON(PASSIVE OPTICAL NETWORK)
Theoretical capacities of other
Medias
• Cu=Short distance could for a 8Mbps
Similarly :
• Microwave radio=STM 16 =More than 2.5Gbps
• Satellite=STM 1= 155.52 Mbps
• Coaxial cable=Approximately 1.5 Gbps
Basic Principles
Principle of step & graded index fibers
Attenuations in fibre
Basic principle of dispersion
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Dispersion is a little complex than attenuation
Dispersion is a process whereby optical pulses are widened as they travel along an
optical fibre. It is caused by the different wavelength components of a light signal
of finite spectral width traveling down the fiber at different velocities.The effect is
a pulse at the terminating end of a fibre that is a wider than the original pulse that
was transmitted.If the amount if widening is excessive, the individual pulses will
not be distinguishable by the receiver.
IN
OUT
Chromatic Dispersion
Variation of refractive index with wavelength of light
 The two main underlying mechanisms, material dispersion and
waveguide dispersion, naturally cancel one another, giving a zero
dispersion point 0
 Control of the refractive index profile can place 0 anywhere in the
1300/1550nm wavelength range
The fibre characteristics are controlled by careful design of the
chemical composition (doping) of the glass used
Dispersion is quoted in terms of the dispersion parameter ‘D’ with
units ps/(nm.km)
An indication of the pulse broadening is given by:
(D * (spectral width of the optical source) *(link distance))
Slide 15
Optical transmission system concepts
The basic components
– A serial bit stream in electrical form is presented to
a modulator, which encodes the data appropriately
for fibre transmission
Basic Concept of LED
• Like a normal diode, the LED consists of a chip
of semiconducting material impregnated, or
doped, with impurities to create a p-n
junction. As in other diodes, current flows
easily from the p-side, or anode, to the n-side,
or cathode, but not in the reverse direction.
Charge-carriers—electrons and holes—flow
into the junction from electrodes with
different voltages. When an electron meets a
hole, it falls into a lower energy level, and
releases energy in the form of a photon.
Contd….
• The wavelength of the light emitted, and
therefore its color, depends on the band gap
energy of the materials forming the p-n
junction. In silicon or germanium diodes, the
electrons and holes recombine by a nonradiative transition which produces no optical
emission, because these are indirect band gap
materials. The materials used for the LED have
a direct band gap with energies corresponding
to near-infrared, visible or near-ultraviolet
light.
Power ratio (Decibel;dB)
• The decibel (dB) is a logarithmic unit of
measurement that expresses the magnitude of a
physical quantity (usually power or intensity) relative
to a specified or implied reference level. Since it
expresses a ratio of two quantities with the same
unit, it is a dimensionless unit.
Examples
• To calculate the ratio of 1 kW (one kilowatt, or 1000 watts) to 1 W in
decibels, use the formula
• Similarly for amplitude ,current or voltage, (power is proportional to the
square of the above 3 quantities. )
Example 1
Answer (Example 1)
Transmitter
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8 Connectors
Receiver
Connector loss= 8*1dB= 8dB
Cable loss= (4*100)/1000=0.4dB
System margin = 5dB
Sensitivity= -30 dB
Transmitter Power = connector loss+cable
loss+system margin+sensitivity
• = 8+0.4+5-30= -16.6dB
Example 2
Answer (Example 2)
Transmitter
2 Connectors
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Receiver
Connector loss= 2*1.5dB = 3 dB
Cable loss= 0.4dB * 50 = 20 dB
System margin = 8 dB
Sensitivity= -34 dB
Transmitter Power = connector loss+cable
loss+system margin+sensitivity
• = 3+20+8-34= -3 dB
• No: of splices= 3/ 0.15 = 20 splices
Example 3 (a)
Example 3 (b)
Example 3 (c)
Example 3 (d)
Example 3 (e)
Example 3 (f)
Example 3 (g)
Example 3 (h)
Optical fibre
C=fλ
C= 3* 108 m/s
Future of optical fibre
The following 2 major factors plays a vital role in designing the maximum
capacity of an optical fibre
• How far the digital multiplexing can be achieved
•As at present , 488ns micro information of a bit pertaining to 2Mbps pcm
stream will be shrinked to 25ps when it goes through stm 64 (10Gbps).If the
technology improves to shrink less than 25ps , then the no of bits in the
higher order pcm will be more than 10Gbps.
•To transmit 10Gbps , the bandwidth required in the optical fibre is around
0.078ns = 78ps ( for 1 wavelength)
•If the available bandwidth in the optical fibre is 200ns , the no; of
wavelengths that can be produced is around 2400 , which will result in
producing a total of 24Tbps.
•Hence both time division multiplexing and dense wave division multiplexing
can further improve the traffic carrying capacity of an optical fibre up to a
total of 24Tbps.
Overview of WDM
Traditional Digital Fiber Optic Transport
Single Pair of Fibers
Digital Transceiver
Digital Transceiver
Single Pair of Fibers
Digital Transceiver
Digital Transceiver
Single Pair of Fibers
Digital Transceiver
Digital Transceiver
Single Pair of Fibers
Digital Transceiver
Digital Transceiver
Digital Fiber Optic Transport using WDM
WDM MUX
WDM MUX
Digital Transceiver
Digital Transceiver
Digital Transceiver
Single Pair of Fibers
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
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Future scenarios
Theoretical Maximum of an optical fibre cable
488 ns
25 ps
TDM
2 Mbps
Transponders
λ1
1
2
Optical Fibre
λ2
10Gbps
2399
2400
λ2399
Only 1 core is needed
λ2400
No of wavelengths = ( 24 * 103 Gb ) / 10 Gb
= 2400 wavelengths
Further study of optical fibre network
Optical signal to noise ratio
ASE=Amplified spontaneous emission
Optical tools for maintanance
• OTDR
• Splicing machine
(OTDR)
Fusion splicing
• It is the process of fusing or welding two fibers together usually by an
electric arc. Fusion splicing is the most widely used method of splicing as it
provides for the lowest loss and least reflectance, as well as providing the
strongest and most reliable joint between two fibers.
• Virtually all singlemode splices are fusion.
• Fusion splicing may be done one fiber at a time or a complete fiber ribbon
from ribbon cable at one time. First we'll look at single fiber splicing and
then ribbon splicing.
•
SEA-ME-WE 4 Cable System Configuration
Diagram
Happy Memories
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Thank You!, Special thanks to Dr. Udawatte.
Wish you an enjoyable stay in your university
Situated in a lovely environment
Christie Alwis
B.Sc (Eng) Hons, MIET (Lond), C.Eng Lond,
FIESL (SL)
• Former chief network officer in SLT
• Visit www.christiealwis.com under
sabaragamuwa optical fibre 2009