Optical Fiber Losses Quiz
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Questions and Answers

What is the critical angle defined as?

  • A maximum value
  • The angle light propagates down the cable
  • A minimum value (correct)
  • The angle light rays enter the cladding

    • Which term is commonly used to measure the magnitude of the acceptance angle?

  • Numerical aperture (correct)
  • Wavelength
  • Velocity
  • Frequency

    • What does numerical aperture describe in an optical fiber?

  • Ability to resist external light
  • Ability to reduce absorption losses
  • Ability to couple light into the cable from an external source (correct)
  • Ability to convert light to heat

    • What does a larger magnitude of numerical aperture indicate about an optical fiber?

    <p>It will accept more external light</p> Signup and view all the answers

    What do absorption losses in optical fibers result from?

    <p>Impurities absorbing light and converting it to heat</p> Signup and view all the answers

    What are the factors that contribute to absorption losses in optical fibers?

    <p>Ultraviolet absorption, infrared absorption, and ion resonance absorption</p> Signup and view all the answers

    What is the main cause of Rayleigh scattering loss in optical fibers?

    <p>Escape of light rays</p> Signup and view all the answers

    How can chromatic distortion be eliminated in optical fibers?

    <p>Opting for an injection laser diode (ILD)</p> Signup and view all the answers

    What is a common characteristic of microbends in optical fibers?

    <p>They contribute to Rayleigh scattering loss</p> Signup and view all the answers

    Which type of bends in optical fibers are caused by differences in thermal contraction rates?

    <p>Microbends</p> Signup and view all the answers

    Why do light rays emitted from an LED and propagated through an optical fiber experience chromatic distortion?

    <p>Different velocities while propagating in glass</p> Signup and view all the answers

    In optical fibers, what contributes less than 20% to the total attenuation?

    <p>Microbending losses</p> Signup and view all the answers

    What phenomenon occurs when each ray of light in a fiber reaches the far end at a different time?

    <p>Modal dispersion</p> Signup and view all the answers

    In a single-mode step-index fiber, why is modal dispersion virtually eliminated?

    <p>Each ray of light travels the same distance in a given period of time</p> Signup and view all the answers

    What type of fibers show multiple modes of light propagation?

    <p>Multimode graded-index fibers</p> Signup and view all the answers

    Which device is commonly used as a light detector in fiber-optic communications systems?

    <p>PIN diodes</p> Signup and view all the answers

    What is the basic construction of a PIN diode?

    <p>Depletion-layer photodiode</p> Signup and view all the answers

    How does the refractive index affect the velocity of light rays in a fiber?

    <p>Inversely proportional</p> Signup and view all the answers

    What is the Acceptance Angle or Acceptance Cone Half Angle?

    <p>The maximum angle at which external light rays may strike the air/fiber interface and still propagate down the fiber</p> Signup and view all the answers

    What is Numerical Aperture (NA) used to measure?

    <p>The light gathering or light collecting ability of the optical fiber</p> Signup and view all the answers

    Which of the following is a requirement for light sources used in optical transmission?

    <p>Produce nearly monochromatic light</p> Signup and view all the answers

    What type of light sources are Light Emitting Diodes (LEDs)?

    <p>Low-cost, low-heat, non-coherent injection light sources</p> Signup and view all the answers

    What makes Injection Laser Diodes (ILDs) stand out among light sources?

    <p>They make the most efficient use of electric energy</p> Signup and view all the answers

    What is a key advantage of LEDs in terms of coupling power?

    <p>They can couple about 100uw of power with a 2% coupling efficiency</p> Signup and view all the answers

    What can be a consequence of the imperfections in the mechanical interface used to house the light detector and attach it to the cable?

    <p>Introduction of losses to the system</p> Signup and view all the answers

    What type of loss can be introduced due to splicing multiple sections of optical cable together?

    <p>Losses ranging from a couple tenths of a dB to several dB</p> Signup and view all the answers

    In fiber optics, what can happen if an optical cable is bent at too large an angle?

    <p>Introduction of losses ranging from a few tenths of a dB to several dB</p> Signup and view all the answers

    How do splices in optical cables impact the signal according to the text?

    <p>Signal loss introduction</p> Signup and view all the answers

    What is the primary concern when an optical cable undergoes large angle bending?

    <p>Loss of total reflections leading to signal loss</p> Signup and view all the answers

    What is the impact of imperfections in the mechanical interface on the light entering the detector according to the text?

    <p>Prevention of some power from entering the light detector</p> Signup and view all the answers

    Study Notes

    Acceptance Angle and Numerical Aperture

    • Acceptance angle (θin) is the maximum angle at which external light rays can strike the air/fiber interface and still propagate down the fiber.
    • Numerical aperture (NA) is a figure of merit that measures the light-gathering or light-collecting ability of an optical fiber.
    • NA = sin θin = √(N1² - N2²)

    Light Sources

    • Light sources must have a wavelength between 300 microns and 0.5 microns.
    • Requirements for light sources:
      • Monochromatic light (single frequency)
      • Capable of being easily modulated (PCM) for better noise immunity
      • High intensity light output
      • Small, compact, and easily coupled to fibers
      • Inexpensive to manufacture
    • Light Emitting Diodes (LEDs) are low-cost, low-heat, and reliable light sources.
    • Injection Laser Diodes (ILDs) make efficient use of electric energy.

    Optical Fiber Losses

    • Absorption losses: impurities in the fiber absorb light and convert it to heat.
    • Factors contributing to absorption losses:
      • Ultraviolet absorption
      • Infrared absorption
      • Ion resonance absorption
    • Rayleigh scattering loss: light rays that escape due to impurities in the fiber.
    • Chromatic dispersion: different wavelengths of light travel at different velocities, causing chromatic distortion.

    Radiation Losses

    • Caused by small bends and kinks in the fiber.
    • Types of bends:
      • Microbends: miniature bends or geometric imperfections along the axis of the fiber.
      • Constant-radius bends: bends with a constant radius.
    • Occurs in multimode fibers, where different rays of light take different paths.
    • Results in a stretched pulse that is reduced in amplitude at the output of the fiber.

    Light Detectors

    • PIN diodes: depletion-layer photodiodes used to detect light energy in fiber-optic communications receivers.
    • APDs: used to detect light energy in fiber-optic communications receivers.

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    Description

    Test your knowledge about the different types of losses that occur in optical fiber systems, such as absorption, scattering, connector loss, and splicing loss.

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