Fiber Optic Communication (FOC) SPPU Endsem Question Paper Nov 2025

Questions

1. Q1

   1. a)

      Explain the working of A valanche photodetector with a neat diagram.

      [6]
   2. b)

      Define the term quantum efficiency and the responsivity of a photodetector. How the quantum efficiency and the responsivity of a photodetector are related to each other.

      [6]
   3. c)

      When 3 × 10 11 photons each with a wavelength of 0.85 × 10 –6 m are incident on a photodiode on average l.2 × 10 11 electrons are collected at the terminals of the device. Determine the quantum efficiency and the responsivity of the photodiode at 0.85  m.

      Also asked:May 2025 ·Nov 2023

      [6]
   OR

2. Q2

   1. a)

      Explain the following terms in terms of an optical detector. i) Dark Current Noise ii) Quantum Noise iii) Thermal Noise

      [6]
   2. b)

      Describe the basic detection process in a photoconductive detector. Also, state any two advantages and disadvantages of a photodiode.

      [6]
   3. c)

      An avalanche photodiode has a quantum efficiency of 45% at 0.85  m. When illuminated with radiation of this wavelength it produces an output photocurrent of 10  A after avalanche gain with a multiplication factor of 250. Calculate the received optical power to the device. 2

      [6]

3. Q3

   1. a)

      Explain in detail the importance of budgets. What are the different system considerations for the rise time budget? Explain with equations.

      [6]
   2. b)

      Enlist the system design considerations for an optical communication network.

      [6]
   3. c)

      An engineer has the following components available i) GaAlAs laser diode operating at 850 nm and capable of coupling 1 mW (0 dbm) into a fiber ii) 10 sections of cable each of which is 500m long has a 4 db/km attenuation and has connectors on both ends. iii) Connector loss of 2 db/connector iv) A pin Photodiode receiver v) An avalanche photodiode receiver Using these components, the engineer, wishes to construct a 5 km link operating at 20 Mb/s. If the sensitivities of the PIN and APD receivers are –45 dbm and –56 dbm respectively, which receiver should be used if a 6 dB system operating margin is required?

      [6]
   OR

4. Q4

   1. a)

      Write a short note on : i) Optical Isolators ii) Optical circulators

      Also asked:Nov 2024

      [6]
   2. b)

      With the help of neat sketch describe WDM architectures.

      [6]
   3. c)

      This part has equations that don’t show as text. Open the PDF to read it.

      [6]

5. Q5

   1. a)

      Explain the desirable properties of optical network with advantages.

      [6]
   2. b)

      Describe the Gigabit Passive Optical Network (GPON) using an appropriate diagram.

      Also asked:May 2025

      [6]
   3. c)

      Compare Asynchronous and Synchronous Optical Network. 3

      [5]
   OR

6. Q6

   1. a)

      What is FTTX? Draw and Explain the architecture of FTTX.

      [6]
   2. b)

      Explain the concept of FDDI with an appropriate diagram.

      [6]
   3. c)

      Compare Active Optical Network (AON) and Passive Optical Network (PON).

      Also asked:May 2025 ·Nov 2024

      [5]

7. Q7

   1. a)

      Using an appropriate diagram,describe and explain the experimental setup used in the OTDR technique.

      [6]
   2. b)

      Describe the Eye Diagram Test. Give an explanation of the basic measuring parameter.

      [6]
   3. c)

      Explain the experimental setup for the time-domain fiber dispersion measurement with suitable diagram.

      [5]
   OR

8. Q8

   1. a)

      Draw and explain the schematic of the experimental setup used to calculate fiber attenuation using the cutback method.

      [6]
   2. b)

      Explain optical spectrum analyzer in detail.

      [6]
   3. c)

      This part has equations that don’t show as text. Open the PDF to read it.

      [5]