Chapter%20One:%20Introduction%20to%20Fiber%20Optics%20Communication%20System

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Chapter OneIntroduction to Fiber Optics
Communication System
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(No Transcript)
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What is Fiber Optic?

• Fiber optics
• A means to carry information from one point to
  another or serves as transmission medium (optical
  fiber).
• A technology that uses thin strand of glass (or
  plastic) threads (fibers) to transmit data.
• A fiber optic cable consists of a bundle of glass
  threads, each of which is capable of transmitting
  messages modulated onto light waves.

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Introduction

• An optical fiber is essentially a waveguide for
  light
• It consists of a core and cladding that surrounds
  the core
• The index of refraction of the cladding is less
  than that of the core, causing rays of light
  leaving the core to be refracted back into the
  core
• A light-emitting diode (LED) or laser diode (LD)
  can be used for the source

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Optical Fiber
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Optical Fiber

• Optical fiber is made from thin strands of either
  glass or plastic
• It has little mechanical strength, so it must be
  enclosed in a protective jacket
• Often, two or more fibers are enclosed in the
  same cable for increased bandwidth and redundancy
  in case one of the fibers breaks
• It is also easier to build a full-duplex system
  using two fibers, one for transmission in each
  direction

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History
1870s John Tyndall showed a beam of light would follow a specific path by refraction
1880, William Wheeling received a patent doing same thing with mirrored pipe. Alexander Graham Bell patented an optical telephone system, which he called the Photophone. However, his earlier invention, the telephone, was more practical and took tangible shape.
1950s saw development of the fiberscope
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History
1957 Lasers first used as light source. Light has an information-carrying capacity 10,000 times that of the highest radio frequencies being used.
1970 Drs. Robert Maurer, Donald Keck, and Peter Schultz of Corning succeeded in developing a glass fiber that exhibited attenuation at less than 20 dB/km, the threshold for making fiber optics a viable technology. It was the purest glass ever made.  the U.S. Navy fiber optic telephone link aboard the U.S.S. Little Rock.
1976 Air Force followed suit by developing its Airborne Light Optical Fiber Technology (ALOFT)
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History
1977 both ATT and GTE installed fiber optic telephone systems in Chicago and Boston respectively.
1980 broadcasters of the Winter Olympics, in Lake Placid, New York, requested a fiber optic video transmission system for backup video feeds. The fiber optic feed, because of its quality and reliability, soon became the primary video feed, making the 1980 Winter Olympics the first fiber optic television transmission.
1990 Bell Labs transmitted a 2.5 Gb/s signal over 7,500 km without regeneration. The system used a soliton laser and an erbium-doped fiber amplifier (EDFA) that allowed the light wave to maintain its shape and density.
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History
1990 Bell Labs transmitted a 2.5 Gb/s signal over 7,500 km without regeneration. The system used a soliton laser and an erbium-doped fiber amplifier (EDFA) that allowed the light wave to maintain its shape and density.
1994 Winter Olympics in Lillehammer, Norway, fiber optics transmitted the first ever digital video signal, an application that continues to evolve today. .
1998 transmitted 100 simultaneous optical signals each at a data rate of 10 gigabits (giga billion per second) distance of nearly 250 miles (400 km).
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Advantages

• The advantages of fiber-optic systems warrant
  considerable attention.
• This new technology has clearly affected the
  telecommunications industry and will continue to
  thrive due to the numerous advantages it has over
  its copper counterpart.
• The major advantages include.

• Wide Bandwidth
• Low Loss Electromagnetic Immunity
• Light Weight
• Small Size
• Noise Immunity and Safety Security
• Economic
• Reliability

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Wide Bandwidth

• Fiber optic communications can run at10 Ghz and
  have the potential to go as high as 1 Thz
  (100,000 GHz).
• A 10 Ghz capacity can transmit (per second)
• 1000 books
• 130,000 voice channels
• 16 HTDV channels or 100 compressed HDTV channels.
• Separate Voice, data and video channels are
  transmitted on a single cable.

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Electromagnetic Immunity

• Copper cables can act as an antennae picking up
  EMI from power lines, computers, machinery and
  other sources.
• Fiber is not susceptible to Electro-Magnetic
  Interference and thus no interference allowing
  error-free transmissions.

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Light Weight and Volume

• Comparison
• Fiber 4kg or 9lb per 1000 ft. (due mainly to
  packaging).
• Coax 36kg or 80lb per 1000 ft.
• Fiber optic cables are substantially lighter in
  weight and occupy much less volume than copper
  cables with the same information capacity.
• Fiber optic cables are being used to relieve
  congested underground ducts in metropolitan and
  suburban areas.
• For example, a 3-in. diameter telephone cable
  consisting of 900 twisted-pair wires can be
  replaced with a single fiber strand 0.005 inch.
• In diameter (approximately the diameter of a hair
  strand) and retain the same information carrying
  capacity.

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Small Size

• Use where space is at a premium
• Aircraft, submarines
• Underground conduit
• High density cable areas Computer centers.

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Noise Immunity and Safety

• No electricity thus no spark hazards so can be
  used through hazardous areas.
• Because fiber is constructed of dielectric
  materials, it is immune to inductive coupling or
  crosstalk from adjacent copper or fiber channels.
  
• In other words, it is not affected by
  electromagnetic interference (EMI) or
  electrostatic interference.

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Security

• Since fiber does not carry electricity, it emits
  no EMI which could be used for eavesdropping.
• Difficult to 'tap' cable must be cut and
  spiced.
• Because light does not radiate from a fiber optic
  cable, it is nearly impossible to secretly tap
  into it without detection.
• For this reason, several applications requiring
  communications security employ fiber-optic
  systems.
• Military information, for example, can be
  transmitted over fiber to prevent eavesdropping.
• In addition, metal detectors cannot detect
  fiber-optic cables unless they are manufactured
  with steel reinforcement for strength.

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Economics

• Presently, since the cost of fiber is comparable
  to copper it is expected to drop as it becomes
  more widely used.
• Because transmission losses are considerably less
  than for coaxial cable, expensive repeaters can
  be spaced farther apart.
• Fewer repeaters mean a reduction in overall
  system costs and enhanced reliability.

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Reliability

• Once installed, a longer life span is expected
  with fiber over its metallic counterparts,
  because it is more resistant to corrosion caused
  by environmental extremes such as temperatures,
  corrosive gases, and liquids.

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Disadvantages of Fiber-Optic System

• In spite of the numerous advantages that
  fiber-optic systems have over conventional
  methods of transmission, there are some
  disadvantages, particularly because of its
  newness.
• Many of these disadvantages are being overcome
  with new and competitive technology. The
  disadvantages include
• Interfacing Costs
• Strength
• Remote powering of devices
• Inability to interconnected

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Interfacing Costs

• Electronic facilities must be converted in order
  to interface to the fiber.
• Often these costs are initially overlooked.
• Fiber-optic transmitters, receivers, couplers,
  and connectors, for example, must be employed as
  part of the communication system.
• Test and repair equipment is costly.
• If the fiber-optic cable breaks, splicing can be
  costly and tedious task.
• Manufacturers in this related field however are
  continuously introducing new and improved field
  repair kits.

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Strength

• Optical fiber , by itself has a significant lower
  tensile strength than coaxial cable.
• Surrounding the fiber with stranded Kevlar (A
  nonmetallic, difficult to-stretch, strengthening
  material) and a protective PVC jacket can help to
  increase the pulling strength.
• Installations requiring greater tensile strengths
  can be achieved with steel reinforcement.

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Remote Powering Of Devices

• Occasionally, it is necessary to provide
  electrical power to a remote device.
• Because this cannot be achieved through the
  fiber, metallic conductors are often included in
  the cable assembly.
• Several manufacturers now offer a complete line
  of cable types, including cables manufactured
  with both copper wire and fiber.

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Inability to interconnect

• Inability to interconnect easily requires that
  current communication hardware systems be
  somewhat retrofitted to the fiber-optic networks.
  
• Much of the speed that is gained through optical
  fiber transmission can be inhibited at the
  conversion points of a fiber-optic chain.
• When a portion of the chain experiences heavy
  use, information becomes jammed in a bottleneck
  at the points where conversion to, or from,
  electronic signals is taking place.
• Bottlenecks like this should become less frequent
  as microprocessors become more efficient and
  fiber-optics reach closer to a direct electronic
  hardware interface.

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Advantage
Bandwidth High bandwidth and capacity Lower signal attenuation (loss)
Immunity to Electrical Noise, Electromagnetic Immunity Immune to noise (electromagnetic interference EMI No crosstalk Lower bit error rates
Signal Security Difficult to tap Nonconductive (does not radiate signals)
Size and Weight Reduced size and weight cables
Overall System Economy Low overall system cost Lower installation cost
Reliability Less restrictive in harsh environments
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Disadvantage
Interfacing Costs High planning, installation, and maintenance cost
Strength lower tensile strength than coaxial cable
Remote Powering of Devices necessary to provide electrical power to a remote device. Cannot be achieved through the fiber, metallic conductors are often included in the cable assembly.
Inability to interconnect incompatibility with the electronic hardware systems that make up today's world.
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Fiber Optic Block Diagram

• Fiber optics is a medium for carrying information
  from one point to another in the form of light.
• Unlike the copper form of transmission, fiber
  optics is not electrical in nature.
• A basic fiber optic system consists of
• i) transmitting device that converts an
  electrical signal into a light signal,
• ii) optical fiber cable that carries the light,
• iii) receiver that accepts the light signal and
  converts it back into an electrical signal.

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Block Diagram
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Transmitter

• Its main function is to transmit the information
  signals like voice, video or computer in the form
  of light signals.
• As shown above, the information at input is
  converted into digital signals by coder or
  converter circuit.
• This circuit is actually ADC (analog to digital
  converter).
• Thus, it converts analog signals into
  proportional digital signals.
• If the input signals are computer signals, they
  are directly connected to light source
  transmitter circuit

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Cont

• The light source block is a powerful light
  source.
• It is generally a FOCUS type LED or low intensity
  laser beam source or in some cases infrared beam
  of light is also used. 
• The rate, at which light source turns ON/OFF,
  depends on frequency of digital pulses.
• Thus, its flashing is proportional to digital
  input.
• In this way, digital signals are converted into
  equivalent light pulses and focused at one end of
  fiber-optic cable.
• They are then received at its other end.

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Fiber Optic Cable

• When light pulses are fed to one end of
  fiber-optic cable, they are passed on to other
  end.
• The cable has VERY LESS attenuation (loss due to
  absorption of light waves) over a long distance.
• Its bandwidth is large hence, its information
  carrying capacity is high.

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Receiver

• At receiving end, a light detector or photocell
  is used to detect light pulses.
• It is a transducer, which converts light signals
  into proportional electrical signals.
• These signals are amplified and reshaped into
  original digital pulses, (while reshaping,
  distortion noise are filtered out) with the
  help of shaper circuit.
• Then the signals are connected to decoder. It is
  actually ADC circuit (Analog to Digital
  Converter), which converts digital signals into
  proportional analog signals like voice, video or
  computer data.
• Digital signals for computer can be directly
  taken from output of shaper circuit

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Cont

• Thus, this total unit is used fiber optic
  communication system.
• However if the distance between transmitter and
  receiver is very large, then REPEATER UNITS are
  used.
• Due to repeaters signals attenuation is
  compensated.
• For this, light signals at far end are converted
  into electrical signals, amplified and
  retransmitted.
• Such repeater unit is also called RELAY STATION

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Application

• Analog system
• Digital system
• Undersea cable
• High Definition Television (HDTV)
• Triple Play Technology ( voice, video , data )

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Quick Test ?

1. Define fiber optic?
2. The advantages of fiber optic, overcome its
   disadvantages. Explain the advantages and
   disadvantages of fiber optic.
3. Draw the block diagram of fiber optic
   communication system.
4. State the function of each block in the diagram.

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Quick Test ?

• Which of the following answer, describe the
  application of fiber optic in communication
  system.
• Triple Play System
• Undersea Communication Cable
• Digital Transmission System
• Weather forecast System