JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year OPTICAL COMMUNICATIONS Previous Question Paper (July - 2023 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Define acceptance angle and numerical aperture.
Answer
The acceptance angle is the maximum angle of incidence at the fiber core face for which light will be coupled into the fiber and propagate by total internal reflection. The numerical aperture (NA) is a dimensionless measure of the light-gathering capacity of an optical fiber, defined as the sine of the acceptance angle, expressed as NA = sin(θa) = √(n12 - n22), where n1 and n2 are the refractive indices of the core and cladding, respectively.
Explain the concept of skew rays.
Answer
Skew rays are light rays that do not intersect the fiber axis during propagation. Unlike meridional rays, which travel in a single plane containing the fiber axis, skew rays follow a helical path around the axis. They contribute to the total light-carrying capacity of the fiber but have different propagation characteristics and travel times compared to meridional rays.
Define group delay in optical fibers.
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Describe the concept of pulse broadening in optical fibers.
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Define the power bandwidth product for LEDs.
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Discuss the factors that affect the quantum efficiency of LEDs.
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Define quantum limit.
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What is the role of analog receivers in optical communication?
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What is Link Power Budget?
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What are the types of dispersion and their impact on signal transmission in optical fiber systems?
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Part B
Explain the concept of cut-off wavelength in single-mode fibers and its significance in signal transmission.
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Define mode field diameter and effective refractive index in single-mode fibers and discuss their importance.
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Explain how the refractive index profile affects the transmission characteristics in ray theory transmission.
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Discuss the concept of bandwidth in graded index fibers and how it is influenced by the refractive index profile.
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Explain waveguide dispersion and discuss its impact on signal distortion in optical fibers.
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Explain the concept of attenuation in optical fibers. Discuss the different types of losses contributing to attenuation, including absorption, scattering, bending, core, and cladding losses.
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Explain the different types of optical fiber connectors used in optical communication systems. Discuss their characteristics, advantages, and applications.
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Explain the concept of splicing in optical fiber connections. Discuss the different techniques used for fiber splicing and their advantages and limitations.
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Describe the factors that affect the quality and reliability of fiber splices. Discuss the methods used for testing and evaluating the performance of fiber splices.
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Discuss the challenges and considerations specific to splicing multimode fibers. Explain the techniques used for achieving low joint loss in multimode fiber joints.
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Explain the concept of equilibrium Numerical Aperture (NA) in power launching. Discuss its significance and the techniques used for achieving optimal NA matching between the source and the fiber.
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Describe the output patterns and power coupling in source-to-fiber power launching.
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Discuss the temperature effect on avalanche gain in APD optical detectors. Explain how temperature variations can impact the performance of APD devices?
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Explain the fundamental operation of an optical receiver. Discuss the key components and their roles in converting optical signals to electrical signals.
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Describe the process of digital signal transmission in optical receivers. Discuss the error sources and the techniques used for error detection and correction.
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Explain the concept of the probability of error in optical receivers. Discuss the factors that influence the probability of error and the methods used to minimize it.
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Explain the concept of link power budget in optical communication. Provide examples and discuss how link power budget calculations are performed?
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Explain the concept of line coding in optical links. Discuss the different line coding techniques used for encoding and decoding digital signals in optical communication systems.
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