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Fiber Optical Communication


Introduction Fiber Optical Communication ... – PowerPoint PPT presentation

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Title: Fiber Optical Communication

  • Introduction
  • Fiber Optical Communication

  • Advantages of Fiber Optics.
  • Fiber-Optic Communications
  • How Does an Optical Fiber Transmit Light?
  • How Are Optical Fibers Made?
  • What You Need to Know?
  • What Do Fiber Optics Benefit Us?

How Fiber Optics Work?
  • You hear about fiber-optic cables whenever people
    talk about the telephone system, the cable TV
    system or the Internet. Fiber-optic lines are
    strands of optically pure glass as thin as a
    human hair that carry digital information over
    long distances. They are also used in medical
    imaging and mechanical engineering inspection

Advantages of Fiber Optics
  • Less signal degradation - The loss of signal in
    optical fiber is less than in copper wire.
  • Light signals - No interference with those of
    other fibers in the same cable.
  • Low power - Signals in optical fibers degrade
    less and need lower-power transmitters.
  • Light weight - An optical cable weighs less than
    a comparable copper wire cable. Fiber-optic
    cables take up less space in the ground
  • Thinner - Optical fibers can be drawn to smaller
    diameters than copper wire.
  • Higher bandwidth The information-carrying
    capacity of a fiber is greater that that id
    twisted-pair cable.
  • Digital signals - Optical fibers are ideally
    suited for carrying digital information, which is
    especially useful in computer networks.
  • Non-flammable - Because no electricity is passed
    through optical fibers, there is no fire hazard..

Fiber-Optic Communications
Optical Regenerator - May be necessary to boost
the light signal (for long distances)
Optical Fiber Conducts the light signals over a
Optical Receiver Receives and decodes the light
Transmitter Produces and encodes the light
  • The transmitter is like the sailor on the deck of
    the sending ship. It receives and directs the
    optical device to turn the light "on" and "off"
    in the correct sequence, thereby generating a
    light signal.
  • Produces and encodes the light signals.

  • Light Source
  • Lasers-narrow spectrum 13 nm, high speed Gb/s
  • LEDs-10BASE-FL LED 830 870 nm, low band width
  • VCSELs are faster, more efficient, and produce a
    smaller divergence beam than LEDs.
  • Wavelength (infrared, non-visible portions of the
  • 1,550 nm-high speed, long distance, single mode
    losslt1 dB/km
  • 1,300 nm- single mode/multi mode(1.5 dB/km)
  • 850 nm - multi mode loss 3.5 dB/km

Fiber Optic Connectors
SC Subscriber Connector (NTT)
ST Straight Tip (ATT Trademark)
Small-Form-Factor, SFF connectors
MT-RJ (AMP, Tyco Electronics)
LC (Lucent Technology, 1.25 mm ferrule)
Fiber Optic Connectors
Fiber Optic Connector Alignment
  • Ferrule-most traditional connector use 2.5 mm
    ferrule as fiber-alignment mechanism

Connector Ferrule Shapes Polishes
  • Insertion loss is the loss of optical power
    contributed by adding a connector to a line.

Connector and Splice Loss Mechanisms
Optical Regenerator
  • Signal loss occurs when the light is transmitted
    through the fiber, especially over long distances
  • Optical Regenerators is spliced along the cable
    to boost the degraded light signals.
  • Consists of optical fibers with a special coating
  • Regenerator is a laser amplifier for the incoming

Optical Receiver
  • Optical receiver is like the sailor on the deck
    of the receiving ship.
  • Takes the incoming digital light signals, decodes
    them and sends the electrical signal to the other
    user's computer, TV or telephone (receiving
    ship's captain).
  • The receiver uses a photocell or photodiode to
    detect the light.

How Does an Optical Fiber Transmit Light?
  • Shine a flashlight beam down a long, straight
  • Total internal reflection.
  • Light signal degrades within the fiber
  • Signal degrades depends on the purity of the
    glass and the wavelength of the transmitted light
  • 850 nm 60 to 75 percent/km
  • 1,300 nm 50 to 60 percent/km
  • 1,550 nm is greater than 50 percent/km

Physics of Total Internal Reflection
What are Fiber Optics?
  • Core - Thin glass center of the fiber where the
    light travels.
  • Cladding - Outer optical material surrounding the
    core that reflects the light back into the core.
  • Buffer coating - Plastic coating that protects
    the fiber from damage and moisture.
  • 9/125/250, 62.5/125/250

Single Mode v.s. Multi Mode
Single Mode
Multi Mode
Step Index Core v.s. Graded Index Core for Multi
Step-index Fiber Fiber that has a uniform index
of refraction throughout the core that is a step
below the index of refraction in the cladding
Graded-index Fiber Optical fiber in which the
refractive index of the core is in the form of a
parabolic curve, decreasing toward the cladding
Classes of Fiber Optics
How Are Optical Fibers Made?
  • Optical fibers are made of extremely pure optical
  • Making a preform glass cylinder
  • Drawing the fibers from the preform
  • Testing the fibers

Making a preform glass cylinder
Modified Chemical Vapor Deposition (MCVD)
  • Oxygen is bubbled through solutions of silicon
    chloride (SiCl4), germanium chloride (GeCl4)
    and/or other chemicals.
  • Precise mixture governs the various physical and
    optical properties (index of refraction,
    coefficient of expansion, melting point, etc.).
  • The gas vapors are then conducted to the inside
    of a synthetic silica or quartz tube (cladding)
    in a special lathe
  • As the lathe turns, a torch is moved up and down
    the outside of the tube.

Making a preform glass cylinder
  • The silicon and germanium react with oxygen,
    forming silicon dioxide (SiO2) and germanium
    dioxide (GeO2)
  • The silicon dioxide and germanium dioxide deposit
    on the inside of the tube and fuse together to
    form glass.
  • The purity of the glass is maintained by using
    corrosion-resistant plastic in the gas delivery
    system (valve blocks, pipes, seals) and by
    precisely controlling the flow and composition of
    the mixture.

Drawing Fibers from the preform blank
  • Graphite furnace (1,900 to 2,200 Celsius)
  • Laser micrometer- Fibers are pulled from the
    blank at a rate of 33 to 66 ft/s (10 to 20 m/s)
  • measure the diameter of the fiber
  • feed the information back to the tractor

Testing the Finished Optical Fiber
  • Tensile strength - Must withstand 100,000 lb/in2
    or more
  • Refractive index profile - Determine numerical
    aperture as well as screen for optical defects
  • Fiber geometry - Core diameter, cladding
    dimensions and coating diameter are uniform
  • Attenuation - Determine the extent that light
    signals of various wavelengths degrade over
  • Information carrying capacity (bandwidth) -
    Number of signals that can be carried at one time
    (multi-mode fibers)
  • Chromatic dispersion - Spread of various
    wavelengths of light through the core (important
    for bandwidth)
  • Operating temperature/humidity range
  • Temperature dependence of attenuation
  • Ability to conduct light underwater - Important
    for undersea cables

What You Need to Know?
  • Transmitter Power-Transmitters are rated in dBm.
  • Receiver Sensitivity-The minimum acceptable value
    of received power needed to achieve an acceptable
    BER or performance.
  • Optical Power Budget-Related to transmitter power
    and receiver sensitivity
  • Delay Budget-propagation factor is 0.67c or 5 ns/m

Optical Power Budget
Receiver Sensitivity
Transmitter Power
What You Need to Know?
  • Multi Mode
  • (Transmitter Output Power Specifications Minimum
    Value- Receiver Input Sensitivity Specifications
    Maximum Value)-safety factor dBm M dB/km
  • ((OP) dBm - (ST) dBm) - 5(SF) dBm M
    dB/km   km
  • Single Mode
  • (Transmitter Output Power Specifications Minimum
    Value- Receiver Input Sensitivity Specifications
    Maximum Value) - safety factor dBm S dB/km
    (?1310nm) or 0.25 (?1550nm)
  • ((OP) dBm - (ST) dBm) - 9(SF) dBm

Case Studying
Single Mode Optical Fiber Cables with Loose
Fibers( ITU-T G.652 Standard Single Mode Fibre )
in stranded Tubes for Duct Applications ( Dry
Core Cable Design ), 6 cores with cable
specifications No. LOFC-10001 A  Type of Fiber
  Single Mode, Step IndexMax. Attenuation at
1310 nm    0.40 dB/kmMax. Attenuation at 1550
nm    0.25 dB/kmMode Field Dia. at 1310 nm  
  9.2 um /- 0.4 umMode Field Dia. at 1550 nm  
  10.4 um /- 0.8 umCable Cut-off
Wavelength       lt 1260 nmFlooding
material              Jelly compoundFibres    
  Fibre Reinforced Plastic Rod, FRP dia.   2.2
mmLoose Tubes   Material   Thermoplastic (PBT)
( Page 2 to 6 )
Wavelength 1310 nm TX Output -15 dBm (Single),
-20 dBm (Multi) Max. TX Output -6 dBm (Single),
-14 dBm (Multi) Sensitivity -36 to -32 dBm
(Single), -34 to -30 dBm (Multi) Moxa -15 -
(-32) -9 dBm 0.4 dB/km   20 km
What You Need to Know?
  • Optical Power Budget

What Do Fiber Optics Benefit Us?
  • Immunity for EMI
  • High Bandwidth
  • Long Transmission Distance
  • Safety and Security

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