Fiber Optic

1

• Fiber Optic
• Communication Overview,
• Cable
• Construction,
• Laying Splicing

By OFC faculty, ALTTC, GZB.
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CONTENTS

• 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

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HISTORICAL PERSEPECTIVE(1)

• 1790 Optical telegraph was devised by Claude
  Chappe.
• 1880 Alexander Grahem Bell invented the
  PHOTOPHONE.
• 1940s Optical guides with reflective coating to
  carry visible light.
• 1960Invention 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).

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HISTORICAL PERSEPECTIVE(2)
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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.

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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.

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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.

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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.

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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 Snells
  law
• n1 sin Øi n2 sin Ør

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PRINCIPAL OF TOTAL INTERNAL REFLECTION
n1 1.48 n2 1.46
1
REFLECTED RAYS
INCIDENT RAYS 1
2
i
3
n1
3
2
r
1
n2
REFRACTED RAYS
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THE OPTICAL FIBRE
Refractive index
6-10 ?m
125 ?m
Cladding
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LIGHT PROPAGATION IN FIBRE
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LIGHT PROPAGATION IN FIBRE
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LIGHT PROPAGATION IN FIBRE
1
2
3
3
2
1
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LIGHT PROPAGATION IN FIBRE
1
2
3
3
2
1
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INDEX OF REFRACTION MATERIALS

• Air 1.0
• Carbon dioxide 1.0
• Water 1.33
• Ethyl alcohol 1.36
• Magnesium fluoride 1.38
• Fused silica 1.46
• Polymethyl methacrylate polymer 1.5
• Glass 1.54
• Sodium chloride 1.59
• Zinc sulfide 2.3
• Gallium arsenide 3.35 Silicon 3.5
• Indium gallium arsenide phoshide 3.51
• Aluminium gallium arsenide 3.6
• Germanium 4.0

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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 Plancks constant..
• f frequency.

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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.

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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 gt n2).
• The cladding layer is surrounded by one or more
  protective coating.
• Change in RI is achieved by selectively doping
  the glass perform.

CORE
CLADDING
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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.

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CLASSIFICATION OF OPTICAL FIBRE

• Material Classification
• 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
• 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.

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CLASSIFICATION OF OPTICAL FIBRE
8 - 12 ?m
a) Single mode step-index fiber
50 - 200?m
b) Multi mode step-index fiber
50 ?m
C) Multi mode GRIN fiber
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WINDOW CONCEPT IN SPECTRUM OF OPTICAL FIBER
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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

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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.

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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.
• 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

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• (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.

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• (D) Along rail bridge or crossing
• Through HDPE pipe/PLP pipe protected by RCC
  or iron pipe as
• per the prescribed by railway authority.
• 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.

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LOSSES IN OPTICAL FIBER

• 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.

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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)
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DISPERSION IN FIBER

• 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
• 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).

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BASIC FIBRE OPTIC COMMUNICATIONS

• A basic comm. System consists of a transmitter,
  a receiver, a medium.
• Optical Transmitters
• convert electrical signals to optical.
• Optical Receivers
• convert optical signal to electrical.
• 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.

ELECTRICAL
SIGNAL
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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.

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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,

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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.

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SYSTEM CONSIDERATIONS NUMBER OF CIRCUITS
TRANSMISSION DISTANCE UPGRADABILITY
Fibre Network Fiber Loss
Topology Bandwidth
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Thank You