Telecommunication: Fiber Theory

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  1. How does fiber optics transmit?
    From a source, information is encoded into a signal (digital or analogue), then a light source pulses light down a fiber optic cable, a decoder then changes the is used to change the pulses into readable information by a device (computer).
  2. Medium
    • Any material through which energy propagates over a distance
    • -Sound through water
    • -Light through high purity glass
    • -Radio signal through air
  3. Light
    Electromagnetic energy in the form of photons
  4. Electromagnetic Signal
    Stream of electromagnetic energy traveling in a sinusoidal wave
  5. Wavelength
    Distance between identical points on a wave expressed in nanometers
  6. What spectrum does fiber optic transmitters operate in?
  7. What wavelengths do Visual Fault Locators(VFL) operate in?
  8. What wavelengths does multimode fiber operate in?
    850 and 1300nm
  9. What wavelengths does single-mode fiber operate in?
    1310 and 1550nm
  10. What are the 3 parts to a fiber optic cable?
    • -Coating
    • -Cladding
    • -Core
  11. Index of Refraction
    Comparison between speed of light in a medium and the speed of light in a vacuum. (table is on page 5)

    N= Speed of light in a vacuum/Speed of light in a medium
  12. Core
    Clear solid glass, light guiding region
  13. Cladding
    Clear solid glass, contains the light in the core
  14. Coating
    Acrylate material, protects glass during handling
  15. Reflection
    Bouncing of light
  16. Refraction
    Bending of light
  17. Numerical Aperture (NA)
    • -The measure of the maximum angle of the light entering the end of the fiber that will propagate within the core of the fiber.
    • -Light rays entering the fiber that exceed the angle of the NA will enter the cladding and be lost.
  18. Acceptance Cone
    • -The area in which light must enter to travel through the fiber.
    • -Any light that hits with in the cone will travel down the fiber and have total internal reflection, any light that misses will be lost in the cladding due to refraction.
  19. List the types of optical sources
    • -Light emitting diode (LED)
    • -Vertical cavity surface emitting laser (VCSEL)
    • -Light amplification from the stimulated emission of radiation (LASER)
  20. What are the different characteristics in the types of optical sources?
    Time delay and spectral width
  21. What are characteristics of a LED?
    Low cost, operates at 850 or 1300nm
  22. What are characteristics of a VCSEL?
    Cost less than a LASER, operates at 850nm
  23. What are the characteristics of a LASER?
    High Cost; can operate at 1310, 1490, 1550 or 1625nm
  24. Spectral Width
    Standard term for band of wavelengths, no source emits a single wavelength. (Picture page 9)
  25. Mode
    Single stream of photons that travel in a straight line unless acted upon by the environment.
  26. What is the width of the core in a single-mode fiber cable?
    8.3 micrometers
  27. What is the width of the core in a multimode fiber cable?
    50 or 62.5 micrometers
  28. Bandwidth
    Capacity of a medium to carry information over a distance in a given amount of time without loss of data. Measured in bits/second
  29. What can affect bandwidth?
    • -The optical source-┬ánominal wavelength, spectral width, time delays
    • - The guide (fiber)- Attenuation and Dispersion
  30. What is attenuation?
    • Loss of signal energy.
    • -Intrinsic
    • -Extrinsic
    • -Expressed in decibels of power lost
    • -Impacts the ability to reach the receiver with sufficient power
  31. What is dispersion?
    • Spreading of signal pulses.
    • -Modal
    • -Chromatic
    • -Impacts the ability to distinguish discrete signals
  32. Intrinsic Attenuation
    • Can not be affected by outside influences.
    • -Absorption- caused by impurities of the glass
    • -Scattering
    • -The manufacturer controls IA
  33. Extrinsic Attenuation
    • Caused by outside influences.
    • -Macrobends
    • -Microbends
    • -Imperfect junctions
  34. Macrobend
    Caused by incorrect bends of during installation of cable.
  35. Microbend
    A kink or pinch point in the cable.
  36. Dispersion
    Spreading of signal pulses as they travel through fiber. May cause pulses to overlap as the arrive at the receiver, this causes bit errors.
  37. Modal Dispersion
    • Spreading of signal pulses due to several modes taking different paths.
    • -Prevalent in multimode fiber.
  38. Chromatic Dispersion
    Caused by the existence of multiple wavelengths within each signal pulse.
  39. Waveguide Dispersion
    Caused by light traveling in the cladding of the cable.
  40. Why use fiber optics?
    • -Superior performance
    • -Ease of installation
    • -Reliability
    • -Secure(difficult to hack or tap)
    • -Easy to upgrade
  41. List some fiber applications
    • -Long distance telephone
    • -Cable TV
    • -Traffic control
    • -Military use
    • -Factory automation
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Telecommunication: Fiber Theory
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