Optical Communication Systems
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Questions and Answers

What is the primary function of a regenerator in a transmission medium?

  • To amplify the signal directly
  • To reconstruct the signal (correct)
  • To modulate the input signal
  • To convert light energy to current

    • Which component is used to couple light from the optical fiber into the light detector?

  • Fiber-to-light detector-coupling device (correct)
  • Source-to-fiber coupler
  • Current-to-voltage converter
  • Voltage-to-current converter

    • How does the amount of light emitted by an LED or ILD relate to the drive current?

  • It is proportional to the drive current (correct)
  • It is inversely proportional
  • It has no relation to the drive current
  • It is equal to the drive current

    • What type of diode is commonly used as a light detector?

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

    The function of the voltage-to-current converter in the transmitter is to:

    <p>Modulate current based on input voltage</p> Signup and view all the answers

    What encapsulates the optical fiber in a transmission medium?

    <p>Protective jacket</p> Signup and view all the answers

    Which device is required to convert changes in detector current to changes in voltage?

    <p>Current-to-voltage converter</p> Signup and view all the answers

    What is the main purpose of the source-to-fiber coupler?

    <p>To couple light into the optical fiber</p> Signup and view all the answers

    What is the role of the Kevlar yarn in the optical fiber cable?

    <p>To increase tensile strength and protection</p> Signup and view all the answers

    Which material is often used for reinforcing optical fibers against environmental stress?

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

    What is the disadvantage of optical fiber cables mentioned in the content?

    <p>Low tensile strength</p> Signup and view all the answers

    Which type of construction includes a steel central member?

    <p>Multiple strands cable</p> Signup and view all the answers

    In the context of the optical fiber cables, what is the purpose of the polyurethane-filled outer protective tube?

    <p>To prevent moisture exposure</p> Signup and view all the answers

    Which option describes a typical characteristic required for optical fiber cable construction?

    <p>It must be resistant to jerking forces</p> Signup and view all the answers

    What methodology may be used instead of Maxwell's equations for analyzing the performance of optical fibers?

    <p>Geometric wave tracing</p> Signup and view all the answers

    What does the multiple-strand cable construction incorporate for maximizing its strength?

    <p>A layer of Mylar tape</p> Signup and view all the answers

    What is the formula for calculating power in dBm?

    <p>dBm = 10 log(P / 0.001)</p> Signup and view all the answers

    How does the velocity of electromagnetic waves behave when transitioning from a dense medium to a less dense medium?

    <p>The velocity increases and the light ray refracts away from the normal.</p> Signup and view all the answers

    What is the dBm value for an optical power level of 10 mW?

    <p>10 dBm</p> Signup and view all the answers

    What is the value of dBμ for a power level of 20 μW?

    <p>13 dBμ</p> Signup and view all the answers

    Which of the following statements about light propagation in dense materials is true?

    <p>Light rays change direction when moving from a dense to a less dense medium.</p> Signup and view all the answers

    What happens to light rays when they enter the fiber core from the air?

    <p>They refract toward the normal.</p> Signup and view all the answers

    How is optical power expressed in dBμ calculated?

    <p>dBμ = 10 log(P / 0.000001)</p> Signup and view all the answers

    What happens to light rays when they enter a denser material?

    <p>They slow down and bend toward the normal.</p> Signup and view all the answers

    What is the critical angle (θc) in the context of optical fibers?

    <p>The angle at which total internal reflection occurs.</p> Signup and view all the answers

    What defines the maximum angle at which external light rays may strike the interface and still propagate down the fiber?

    <p>The acceptance angle.</p> Signup and view all the answers

    What is the relationship between frequency and velocity of electromagnetic waves in free space?

    <p>All frequencies travel at the same velocity.</p> Signup and view all the answers

    Using Snell's law, what does the equation for acceptance angle (θin(max)) simplify to for optical fibers?

    <p>θin(max) = sin⁻¹(1.5 - 1.46)</p> Signup and view all the answers

    What is the refractive index of air as stated in the context of optical fibers?

    <p>1.0</p> Signup and view all the answers

    What characterizes an acceptance cone in optical fibers?

    <p>It indicates the boundary for maximum light acceptance into the fiber.</p> Signup and view all the answers

    Which equation represents the relationship between the acceptance angle and refractive indices?

    <p>θin(max) = sin⁻¹(2n1 - n2)</p> Signup and view all the answers

    What role does the cladding play in an optical fiber setup?

    <p>It ensures total internal reflection occurs.</p> Signup and view all the answers

    What causes ion resonance absorption in materials used for optical fibers?

    <p>Hydroxyl (OH-) ions</p> Signup and view all the answers

    During which state is glass molded into optical fiber?

    <p>Plastic state</p> Signup and view all the answers

    What phenomenon results from light rays escaping fiber due to diffraction?

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

    Which of the following can eliminate chromatic distortion in optical fibers?

    <p>Utilizing a monochromatic light source</p> Signup and view all the answers

    What primarily causes radiation losses in optical fibers?

    <p>Microbends and constant-radius bends</p> Signup and view all the answers

    What type of loss occurs when light rays emitted by an LED do not arrive concurrently at the end of a fiber?

    <p>Chromatic distortion</p> Signup and view all the answers

    What are the microscopic irregularities in optical fiber caused by during manufacturing?

    <p>Tension applied during drawing process</p> Signup and view all the answers

    Which type of dispersion is only observed in fibers with a single mode of transmission?

    <p>Chromatic distortion</p> Signup and view all the answers

    Study Notes

    Optical Fiber Transmission Components

    • Regenerators are used in transmission over long distances to reconstruct optical signals rather than amplifying them.
    • The receiver consists of a fiber-to-interface light coupler, a photodetector, and a current-to-voltage converter.
    • Transmitters use infrared LEDs or injection laser diodes (ILDs) modulated by electrical signals to generate light.
    • Light output intensity from LEDs and ILDs is proportional to the input drive current.

    Fiber Optic Construction

    • Optical fibers consist of a core made from glass or plastic, surrounded by cladding and a protective jacket.
    • The fiber-to-light detector coupler optimizes light coupling from the fiber into the light detector, which is typically a PIN diode, APD, or phototransistor.
    • A current-to-voltage converter transforms variations in detector current into output voltage, reflecting the original light input.

    Cable Reinforcement

    • Optical fibers lack inherent tensile strength; reinforcement materials such as steel, Kevlar, and FR-PVC are employed to withstand environmental stresses.
    • The choice of cable construction is influenced by performance requirements along with economic and environmental considerations.

    Light Propagation

    • Light travels at approximately 300,000,000 meters per second in a vacuum, but slows in denser materials, causing refraction.
    • Critical angle determines the maximum angle light rays can strike the air/glass interface to propagate within the fiber.

    Acceptance Angle

    • The acceptance angle is defined by the maximum incidence angle for light to enter the fiber core effectively; calculated using the refractive indices of materials involved.

    Loss Mechanisms in Optical Fibers

    • Absorption losses can result from ion resonance due to water molecules trapped in glass and other metal ions.
    • Rayleigh scattering occurs due to microscopic irregularities formed during fiber manufacturing, leading to light loss through diffraction.
    • Chromatic dispersion happens when multiple wavelengths from an LED travel at different speeds, causing signal distortion.
    • Radiation losses are associated with bends and kinks in fiber, categorized into microbends and constant-radius bends.

    Mathematical Formulas

    • Various equations are available for converting optical power levels into decibels (dBm and dBμ) based on power measurements in watts.
    • Example calculations illustrate the conversions for power levels of 10 mW (10 dBm, 40 dBμ) and 20 μW (-17 dBm, 13 dBμ).

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    Advanced Electronic Communications Systems (6th Edition) PDF

    Description

    This quiz covers essential concepts in optical communication systems, including the function of regenerators in the transmission medium and the components involved in both the transmitter and receiver. Understand how light amplification and signal reconstruction play critical roles in communication technology.

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