Fiber Optic Communication (FOC) SPPU Endsem Question Paper May 2023

Questions

1. Q1

   1. a)

      A photodiode has a quantum efficiency of 65% when photons of energy 1.5 × 10 –19 J are incident upon it. i) at what wavelength is the photodiode operating? ii) Calculate the incident optical power required to obtain a photocurrent of 2.5 μ A.

      [6]
   2. b)

      Define the quantum efficiency and the responsivity of a photodetector. Give the mathematical equations for the same.

      [6]
   3. c)

      Compare PIN diode with APD (any 3 points).

      [6]
   OR

2. Q2

   1. a)

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

      [6]
   2. b)

      What is a photodetector? Discuss various requirements of a photodetector to be used in optical communication.

      [6]
   3. c)

      With the help of diagram explain working of p - n photodiode. Draw its output characteristics.

      [6]

3. Q3

   1. a)

      A 1550-nm single-mode digital fiber optic link needs to operate at 622 Mb/s over 80 km without amplifiers. A single-mode InGaAsP laser launches an average optical power of 13 dBm into the fiber. The fiber has a loss of 0.35 dB/km and there is a splice with a loss of 0.1 dB every kilometer. The coupling loss at the receiver is 0.5 dB and the receiver uses an InGaAs APD with a sensitivity of –39 dBm. Excess- noise penalties are predicted to be 1.5 dB. Setup an optical power budget for this link and find the system margin.

      [6]
   2. b)

      Draw and explain simplex point to point optical link.

      [6]
   3. c)

      Illustrate the working of optical amplifier. Enlist the semiconductor materials used for active medium in DFAs.

      [6]
   OR

4. Q4

   1. a)

      Sketch and explain implementation of a typical WDM network. Enlist some of the active WDM components.

      [6]
   2. b)

      A digital optical fiber system uses an RZ pulse format. An optical fiber link is required to operate over a distance of 10 km without repeaters. The fiber available exhibits a rise time due to intramodal dispersion of 0.2 ns/km. in addition the APD detector has a rise time of 1 ns. Estimate the maximum rise time allowable for the system, if the source has a rise time of 4 ns in order for the link to be successfully operated at a transmission rate of 40 Mbps.

      [6]
   3. c)

      Describe Optical power-loss model. Draw a neat diagram for the same.

      [6]

5. Q5

   1. a)

      With the help of diagram explain various elements used in optical networks. Explain the modularity and scalability features of an optical network.

      [6]
   2. b)

      What are the corresponding levels and bit rates for SDH and SONET? Draw and explain STS-1 frame structure.

      [6]
   3. c)

      i) Calculate how many 64-kb/s voice channels can be carried by an STS-3, STS-48, and STS-192 system. ii) How many 20-Mb/s digitized video channels can be transported over STS-3 systems?

      [5]
   OR

6. Q6

   1. a)

      Draw and explain general structure of a passive optical network (PON).

      [5]
   2. b)

      Compare EPON, APON and GPON (any 3 points).

      [6]
   3. c)

      Explain the following w.r.t. SONET. i) Structure ii) Operation iii) Advantages

      [6]

7. Q7

   1. a)

      Enlist widely used optical system test instruments and explain their functions.

      Also asked:Nov 2023

      [6]
   2. b)

      Draw Schematic experimental setup for determining fiber attenuation by the cutback technique. Explain the same.

      Also asked:Nov 2023

      [6]
   3. c)

      Draw representative trace of backscattered and reflected optical power as displayed on an OTDR screen and explain the meanings of various trace features.

      [5]
   OR

8. Q8

   1. a)

      Illustrate Operational principle of an OTDR using an optical circulator. Draw the corresponding diagram.

      [6]
   2. b)

      Explain Eye diagram test. Define fundamental measurement parameter.

      Also asked:Nov 2023

      [6]
   3. c)

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

      [5]