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 (B)</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 (C)</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 (C)</p> Signup and view all the answers

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

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

How can chromatic distortion be eliminated in optical fibers?

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

What is a common characteristic of microbends in optical fibers?

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

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

<p>Microbends (D)</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 (C)</p> Signup and view all the answers

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

<p>Microbending losses (D)</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 (C)</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 (C)</p> Signup and view all the answers

What type of fibers show multiple modes of light propagation?

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

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

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

What is the basic construction of a PIN diode?

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

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

<p>Inversely proportional (A)</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 (B)</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 (A)</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 (A)</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 (B)</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 (C)</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 (D)</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 (B)</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 (A)</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 (B)</p> Signup and view all the answers

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

<p>Signal loss introduction (B)</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 (A)</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 (A)</p> Signup and view all the answers

Flashcards

Critical Angle

The minimum angle of incidence at which total internal reflection occurs.

Numerical Aperture

A measure of the acceptance angle's magnitude.

Numerical Aperture (in optical fiber)

Describes the optical fiber's ability to couple light from an external source.

Larger Numerical Aperture magnitude

Indicates that the optical fiber will accept more external light.

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Absorption Losses

Result from impurities in the fiber absorbing light and converting it to heat.

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Factors of Absorption Losses

Ultraviolet absorption, infrared absorption, and ion resonance absorption.

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Rayleigh Scattering Loss

Random variations in the fiber's density and composition cause light to scatter in all directions.

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Eliminating Chromatic Distortion

Using an Injection Laser Diode (ILD).

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Microbends Characteristic

They contribute to Rayleigh scattering loss.

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Microbends (cause)

Caused by differences in thermal contraction rates during manufacturing.

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Chromatic Distortion (cause)

Different wavelengths of light travel at different velocities in the glass.

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Microbending loss contribution

Microbending losses contribute less than 20% to the total attenuation of signal.

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Modal Dispersion

Each ray of light reaches the far end of the fiber at a different time.

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Modal Dispersion Elimination

Each ray of light travels the same distance in a given period of time.

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Multiple Modes of Propagation

Multimode graded-index fibers

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Common Light Detector

PIN diodes

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PIN Diode Construction

Depletion-layer photodiode.

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Refractive Index Effect

Inversely proportional.

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Acceptance Angle

The maximum angle at which external light rays may strike the air/fiber interface and still propagate down the fiber.

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Numerical Aperture (NA)

The light gathering or light collecting ability of the optical fiber.

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Requirement for Light Sources

Produce nearly monochromatic light

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Light Emitting Diodes (LEDs)

Low-cost, low-heat, non-coherent injection light sources

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Injection Laser Diodes (ILDs)

They make the most efficient use of electric energy

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LED Coupling Power

They can couple about 100uw of power with a 2% coupling efficiency

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Mechanical Interface Imperfections

Introduction of losses to the system

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Optical Cable Splicing Losses

Losses ranging from a couple tenths of a dB to several dB

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Large Angle Bending Losses

Introduction of losses ranging from a few tenths of a dB to several dB

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Splices Impact on Signal

Signal loss introduction

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Primary Concern with Large Angle Bending

Loss of total reflections leading to signal loss

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Imperfections in the Mechanical Interface

Prevention of some power from entering the light detector

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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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