Fiber Optic
Communication
Overview,
Cable
Construction,
Laying & Splicing
By
OFC faculty, ALTTC,
GZB.
CONTENTS
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HISTORY
ADVANTAGES
APPLICATIONS
FIBER OPTIC PRINCIPLE
WINDOWS OF OPERATION
FIBER CLASSIFICATION
FIBER PROPERTIES
STANDARD FIBER TYPES
A TYPICAL OPTICAL FIBER LINK
CURRENT TRENDS IN FIBER OPTIC COMMUNICATION
OFC Faculty
Optical Fiber Communication
4/9/2015
“HISTORICAL
PERSEPECTIVE”(1)
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1790: Optical telegraph was devised by Claude Chappe.
1880: Alexander Grahem Bell invented the PHOTOPHONE.
1940’s: Optical guides with reflective coating to carry visible light.
1960:Invention of “LASER”-The first major break through in fiber optic
technology. Unguided (non fiber) communication systems were
developed after laser discovery.
1966 Onwards: Development of optical fibers by companies like
Corning Glass (very high loss).
IN 1970, Low loss fiber was developed and OFC system became
practical. It was operated at wave-length around 820 nm and at
attenuation of 1db/km.
Now fibers with losses of only a fraction of 1 db/km are available
(0.15-0.35 db/km).
OFC Faculty
Optical Fiber Communication
4/9/2015
“HISTORICAL
PERSEPECTIVE”(2)
OFC Faculty
Optical Fiber Communication
4/9/2015
ADVANTAGES OF FIBRE
COMMUNICATIONS (1)
• High information carrying capacity:
A valid comparison would be on the basis of cost per meter per
telephone channel, rather than just cost per meter.
• Resource plentiful:
The basic materials are either silicon dioxide for glass fibers or
transparent plastic which are plentiful
• Less attenuation:
A typical fibre attenuation is 0.3 dB/km. Whereas a coaxial
cable (RG-19/U) will attenuate a 100-Mz signal by 22.6 dB/km.
• Greater safety:
Optic fibers glass/plastic, are insulators. No electric current
flows through them.
OFC Faculty
Optical Fiber Communication
4/9/2015
ADVANTAGES OF FIBRE
COMMUNICATIONS (2)
• Immunity to Radio Frequency Interference:
Fibers have excellent rejection of radio-frequency interference
(RFI) caused by radio and television stations, radar, and other
electronics equipment.
• Immunity to Electromagnetic Interference:
Fibers have excellent rejection of electromagnetic interference
(EMI caused by natural phenomena such as lighting, sparking,
etc).
• No cross-talk:
The optic wave within the fiber is trapped and does not leaks
out during transmission to interfere with signals in other fibers.
• Higher Security:
fibers offer higher degree of security and privacy.
OFC Faculty
Optical Fiber Communication
4/9/2015
ADVANTAGES OF FIBRE
COMMUNICATIONS (3)
• Small size and light weight:
typical optical cable has a fiber dia. of 125m, cable
dia. 2.5 mm and weight of 6 kg/km in comparison a
coaxial cable (RG-19/U) has a outer dia. Of 28.4 mm,
and weight 1110 kg/km.
• Corrosion :
Corrosion caused by water/chemicals is less severe
for glass than for copper.
• Less temperature sensitive:
Glass fibers can with stand extreme temperatures
before deteriorating. Temperatures up to 800 C leave
glass fiber unaffected.
OFC Faculty
Optical Fiber Communication
4/9/2015
APPLICATION OF FIBER OPTIC
COMMUNICATIONS
• Telecommunications:
Long-Distance Telecommunications.
Inter-exchange junction.
Fibre in the loop (FITL).
• Video Transmission:
Television broadcast, cable television (CATV), remote monitoring, etc.
• Broadband Services:
provisioning of broadband services, such as video request service,
home study courses, medical facilities, train timetables, etc.
• High EMI areas:
Can be laid along railway track, through power substations and can
be suspended directly from power line towers, or poles.
• Military applications:
• Non-communication fiber optic:
eg. fiber sensors.
OFC Faculty
Optical Fiber Communication
4/9/2015
Optic review
Ray Theory:
• A number of optic phenomena are adequately explained by
considering light as narrow rays.
• The theory based on this approach is called geometrical optics.
• These rays obey a few simple rules:
1. In a vacuum, rays travel at a velocity of c =3x108m/s. In any
other medium, rays travel at a slower speed, given by
v = c/n n =refractive index of the medium.
2. Rays travel straight paths, unless deflected by some change in
medium.
3. If any power crosses the boundary, the transmitted ray direction
is given by Snell’s law:
n1 sin Øi = n2 sin Ør
OFC Faculty
Optical Fiber Communication
4/9/2015
PRINCIPAL OF TOTAL
INTERNAL REFLECTION
n1 = 1.48
n2 = 1.46
1
INCIDENT RAYS 1
2
n1
REFLECTED RAYS
¢i
3
3
2
¢r
n2
OFC Faculty
1
REFRACTED RAYS
Optical Fiber Communication
4/9/2015
THE OPTICAL FIBRE
Refractive index
6-10 m
Core
125 m
Cladding
OFC Faculty
Optical Fiber Communication
4/9/2015
LIGHT PROPAGATION IN
FIBRE
OFC Faculty
Optical Fiber Communication
4/9/2015
LIGHT PROPAGATION IN
FIBRE
OFC Faculty
Optical Fiber Communication
4/9/2015
LIGHT PROPAGATION IN
FIBRE
1
2
3
3
2
1
OFC Faculty
Optical Fiber Communication
4/9/2015
LIGHT PROPAGATION IN
FIBRE
1
2
3
3
2
1
OFC Faculty
Optical Fiber Communication
4/9/2015
INDEX OF REFRACTION
MATERIALS
Air
Carbon dioxide
Water
Ethyl alcohol
Magnesium fluoride
Fused silica
Polymethyl methacrylate polymer
Glass
Sodium chloride
Zinc sulfide
Gallium arsenide
Silicon
Indium gallium arsenide phoshide
Aluminium gallium arsenide
Germanium
OFC Faculty
Optical Fiber Communication
1.0
1.0
1.33
1.36
1.38
1.46
1.5
1.54
1.59
2.3
3.35
3.5
3.51
3.6
4.0
4/9/2015
NATURE OF LIGHT
Wave Nature of Light :
• Many light phenomena can be explained by realizing that light is
an electromagnetic wave having a very high oscillation
frequencies.
• The wavelength of light beam:
 = v/f
v = beam velocity
f = its frequency.
Particle Nature of light :
• Sometimes light behaves as though it is made up of very small
particles called photons. The energy of a single photon is:
Wp = hf joules
h = 6.626 x 10-34 j x s is Planck’s constant..
f = frequency.
OFC Faculty
Optical Fiber Communication
4/9/2015
ELECTROMAGNETIC
SPECTRUM
Visible wavelengths
0.4 m (red)
• Silica glass fiber
attenuates light
heavily in visible
& UV regions.
• Glass fiber is
relatively efficient
in infrared
region.
• Three window of
operation are at
0.85, 1.3 and
1.55 m.
OFC Faculty
1015
ULTRAVIOLET
1014
INFRARED
1013
1012
1011
1010
109
108
107
106
105
104
103
102
101
Optical Fiber Communication
MICROWAVE
RADIO
POWER
4/9/2015
CONSTRUCTION OF OPTICAL
FIBER CABLE
Basic Fibre
• core with R.I., n1 is
supported by
concentric
cladding layer with
R.I. n2.
• R.I. of core is
greater than
cladding (n1 > n2).
• The cladding layer
is surrounded by
one or more
protective coating.
• Change in RI is
achieved by
selectively doping
the glass perform.
OFC Faculty
CORE
CLADDING
Optical Fiber Communication
4/9/2015
CABLING OF OPTICAL
FIBRE
• Cabling is done to protect the fiber during transportation, installation
& operation.
• Cabling protects the optical fibers from mechanical damage and
environmental degradation.
• It resembles conventional metal cables externally.
•
There are a variety of cable design available and irrespective of their
design ,fiber optic cables have the following parts in common :
• Buffer : to protect fiber from outside stress; materials used - nylon,
or plastic.
• Strength member : to reduce stress due to pulling, shearing,
and bending; materials used-textile fibers (kevlar), or steel.
• Cable filling compound: to prevent moisture intrusion and
migration in the cable.
• Cable jacket : to protect the fiber against cut and abrasion;
material used-polyethylene polyurethane, polyvinyl chloride or teflon.
OFC Faculty
Optical Fiber Communication
4/9/2015
CLASSIFICATION OF OPTICAL
FIBRE
Material Classification :
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Liquid core fibre.
All fused-silica-glass fibre: have silica-core and silica-cladding.
Plastic-clad-silica (PCS) fibre: have silica core and plastic cladding.
All-plastic fibre : have both core and cladding made up of plastic.
Compound glass fibre such as fluride glass fibre.
Modal classification :
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Similar to metallic wave guides, there are stable propagation states of
electromagnetic waves in an optical fibre called modes.
Fibers can be classified based on number of modes available for
propagation : Single-mode (SM) fibre
Multi-mode (MM) fibre.
Classification based on refractive index profile :
• Step index (SI) fibre.
• Graded index (GRIN) fibre.
OFC Faculty
Optical Fiber Communication
4/9/2015
CLASSIFICATION OF
OPTICAL FIBRE
8 - 12 m
2a
a) Single mode step-index fiber
2a
50 - 200m
b) Multi mode step-index fiber
2a
50 m
C) Multi mode GRIN fiber
OFC Faculty
Optical Fiber Communication
4/9/2015
5
4
WINDOW CONCEPT IN SPECTRUM
OF OPTICAL FIBER
3
- 190 THz
Cut - off wave length
for single - mode
fibre -
- 50 THz
OH-
2
OH
0
1
OH-
Wavelength (m.)
0.7
0.8
0.9 1.0
1.1
1.2
1.3
First Window
Second Window
Third Window
OFC Faculty
1.4
1.5
1.6
1.7
Fourth Window
Optical Fiber Communication
4/9/2015
LAYING OF CABLE
soil categorization : ( for depth of trench )
(A) Rocky : Cable trench, where it is not possible to be dug without
blasting and/or chiseling.
(B) Non Rocky : Other than ‘A’ above, soil mixed with stone and soft
rock.
Pipes for cable laying
Advantage for using pipes :1.It gives mechanical protection
2.Pipes can be laid in advance so that
the cable laying is faster
(1) HDPE pipe 75 mm (diameter) length 5m. (approx 18 to 20’ )
(2) HDPE pipe 50 mm (diameter) length 5m. (approx 18 to 20’ )
(3) PLP pipe (40 mm. outer diameter ) length 1km/200m
OFC Faculty
Optical Fiber Communication
4/9/2015
LAYING OF CABLE
• Mow manual laying method is discouraged as it is
expensive , time consuming and also due to safety
consideration.
• Now for digging JCB machines are preferred.
• Air blowing method by using Pressure machine is
used for cable laying.
OFC Faculty
Optical Fiber Communication
4/9/2015
LAYING OF CABLE
Measurement of cable depth
Depth should be measured from the top of pipe.
However it is acceptable, if it is less upto eight
cms from the specified depth.
(A) Cross country rout (normal soil):
HDPE pipe or PLP pipe depth is 1.5 meter .
In rocky area minimum depth 0.9 m ( where digging more
then 1 meter above pipe is not possible due to any
Obstruction etc) should be considered. However, all
cables having depth less then 1.2 meter should be
protected by RCC/GI pipes
OFC Faculty
Optical Fiber Communication
4/9/2015
(B) In built up area (city/town/urban area):
(1) OF cable should be laid through exiting duct.
(2) GI pipe or RCC pipe at the entry of duct.
(3) In non duct area it should be laid through HDPE
pipe/PLP pipe at depth of 1.5 meter using RCC/GI pipe for
protection.
(4) Depth in rocky soil may be consider as 0.9 to 1.0 meter
(C) On culvert/bridge over river and nallah:
(1) At the depth of 1.5 meter. Pipe length should be extended upto 2
meters at both ends.
(2) This should be fixed along the parapet wall/bridge wall when
river or nalla is full of water through out year, through fixed GI
pipe on wall at suitable height above the water level.
OFC Faculty
Optical Fiber Communication
4/9/2015
(D) Along rail bridge or crossing :
Through HDPE pipe/PLP pipe protected by RCC or iron pipe as
per the prescribed by railway authority.
(E) On road crossing :
At a depth of 1.5 meter through HDP pipe enclosed in RCC
pipe extended by 3.0 meter to the either side end of the road.
Indicators along route :
(A) Route indicator
At every 200 m route length, showing name of route & no
of indicators.
(B) Joint indicator :
At every joint (Splice), generally it is placed at every
2/4 Km(Drum length)
(C) Branch (Root diversion) indicator:
Provided at route diversion or branching from the main
root.
OFC Faculty
Optical Fiber Communication
4/9/2015
LOSSES IN OPTICAL
FIBER
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There are several points in an optic system where losses occur.
These are: coupler, splices, connectors and the fiber itself.
Losses associated within the fiber classified as under:
Losses due to absorption: Even the purest glass will absorb heavily
within specific wavelength regions. Other major source of loss is
impurities like, metal ions and OH ions.
• Losses due to scattering: caused due to localized variations in
density, called Rayleigh scattering and the loss is:
L = 1.7(0.85/)4 dB/km
 is in micrometers
• Losses due to geometric effect:
– micro-bending.
– macro-bending.
OFC Faculty
Optical Fiber Communication
4/9/2015
GENERAL ANALYSIS OF OTDR
PLOT
• OTDR is used for measurement of splice loss/ fiber loss in a section.
• Optical power meter is used to know total loss of terminated cable
section.
FRESNE REFLECTIONS
LOSS
(db)
SPLICE
CONNECTOR
DISTANCE (KM)
OFC Faculty
Optical Fiber Communication
4/9/2015
DISPERSION IN FIBER
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Dispersion is spreading of the optical pulse as it travels down the length.
Dispersion limits the information carrying capacity of fibre.
Classified as : Material Disp, Waveguide Disp. & Modal Disp.,
• Material Dispersion:
– R.I. varies with Wave length causing velocity variation.
d n2 z
– Pulse spread : (t/L) = - C d2  = - M 
• Waveguide Dispersion:
– effective R.I. varies with wavelength for given film thickness (n eff =
c/vg)
d n2 eff z 
– Pulse spread : (t/L) = - C d2
= - M g 
• Modal Dispersion:
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– pulse spreading caused by various modes.
– Pulse spread:(t/L) = Ln1 2 /2c for GRIN fiber
Total Dispersion = - (M + Mg )  L
for SM fiber
= (modal disp.)2 + (mat. disp.)2 for MM fiber (as MG = 0).
OFC Faculty
Optical Fiber Communication
4/9/2015
BASIC FIBRE OPTIC
COMMUNICATIONS
A basic comm. System consists of : a transmitter, a receiver, &
a medium.
TRANSMITTER
MEDIUM RECIEVER
• Optical Transmitters:
Ligh t
Ligh t
sansor
– convert electrical signals to optical. source
• Optical Receivers:
ELECTRICAL
ELECTRICAL
SIGNAL
– convert optical signal to electrical. SIGNAL
• The basic elements in transmitters: Electronic interfaces,
Electronics processing circuitry, Drive circuitry, light source,
optical interfaces, output sensing and stabilization,
Temperature sensing and control.
• The basic elements in an optical receiver: Detector,
Amplifier, Decision circuits.
OFC Faculty
Optical Fiber Communication
4/9/2015
OPTICAL SOURCES
• The device which actually converts electrical signals to its optical
equipment.
• Most common light sources:
– light-emitting diodes (LEDs) .
– Light Amplification by Stimulated Emission of Radiation
(laser) diodes.
• It is particularly required in lasers to maintain stable output power
by way of feedback mechanism.
• Laser is very sensitive to temperature. Operating characteristics of
a semiconductor laser - notably threshold, current, output power,
and wavelength change with temperature. Hence temperature
sensing and control is required to maintain stable temperature.
OFC Faculty
Optical Fiber Communication
4/9/2015
DETECTORS
• The detectors used in fibre optic communications are
semiconductor photodiodes or photodetectors.
• It converts the received optical signal into electrical
form.
– Pin photodiode: cheaper, less temperature
sensitive, and requires lower reverse bias voltage.
– Aavalanche photodiode (APD): used where
receiver is to detect lower power,
OFC Faculty
Optical Fiber Communication
4/9/2015
SYSTEM DESIGN
• Power budget: for a link to be feasible.
Source Transmitting Power - (coupling Loss to
fibre + Connectors Losses + Fibre Loss + Splicing
Loss Maintenance Margin)  Receiver Sensitivity
• Rise time Budget: to check total link rise i.e. this
time is to be within permissible limit.
OFC Faculty
Optical Fiber Communication
4/9/2015
SYSTEM CONSIDERATIONS
* NUMBER OF CIRCUITS * TRANSMISSION DISTANCE
* UPGRADABILITY
Detectors
* Responsivity
* Dark Current
PIN
APD
* Gain
Sources
* Wavelength
* Line Width
* Rise Time
LED
LASER
Cable network
* Route Loss
* Route BW
* Network Flexibility
Fibre
Loss
OFC Faculty
Network
Topology
APD
PIN
Fiber
Bandwidth
Optical Fiber Communication
4/9/2015
Thank You
OFC Faculty
Optical Fiber Communication
4/9/2015