Question Paper: Optical Communication : Question Paper May 2016 - Electronics and Comm. Engg. (Semester 6) | Gujarat Technological University (GTU)
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## Optical Communication - May 2016

### Electronics and Comm. Engg. (Semester 6)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.
1 (a) Briefly Explain the block diagram of Optical Communication Systems and also mention the advantages of optical fiber communication.(7 marks) 1 (b) With figure explain the plasma activated chemical vapor deposition (PCVD) technique for the production of optical fiber.(7 marks) 2 (a) Derive the equation for the power launched from LED Source in to a S.I. fiber.(7 marks)

### Solve any one question from Q2(b) & Q2(c)

2 (b) A multimode step index fiber with a core diameter of 80 ?m and a relative index difference of 1.5% is operating at a wavelength of 0.85 ?m. If the core refractive index is 1.48, calculate:
(i) Normalized frequency of fiber
(ii) Total number of guided modes.
(7 marks)
2 (c) (i) What is equilibrium numerical aperture? Give the significance of the same.(3 marks) 2 (c) (ii) A step index fiber has ncore=1.44 and nclad=1.40 find
(1) The N.A.
(2) Delta
(3) The acceptance angle.
(4 marks)

### Solve any two question from Q3(a), Q3(b) & Q3(c), Q3(d)

3 (a) Discuss optical power loss model for a point to point link.(7 marks) 3 (b) What are bending losses in fiber optic communication? Describe:
(i) Micro bending losses.
(ii) Macro bending losses.
(7 marks)
3 (c) List the types of Light Emitting Diodes used in optical system and explain any one of them with required figure.(7 marks) 3 (d) Discuss briefly the distributed feedback LASER with neat sketch.(7 marks)

### Solve any two question from Q4(a), Q4(b) & Q4(c), Q4(d)

4 (a) Explain intramodal and intermodal dispersion in details(7 marks) 4 (b) Explain detection process in the p-i-n photodiode. Define the quantum efficiency & responsivity of a photo detector.(7 marks) 4 (c) A Silicon APD has a quantum efficiency of 75 % at a wavelength of 900 nm. If 0.5 mw of optical power produces a multiplied photo current of 10 mA, then what is avalanche gain for this device?(7 marks) 4 (d) (i) Give the comparison of S.I. and G.I. fibers.(4 marks) 4 (d) (ii) Give the comparison of S.M. and M. M. Fibers(3 marks)

### Solve any two question from Q5(a), Q5(b) & Q5(c), Q5(d)

5 (a) Write short notes on Synchronous optical fiber networks (SONET).(7 marks) 5 (b) Explain the principle of operation of (i) EDFA (ii) Wavelength division multiplexing.(7 marks) 5 (c) What is optical coupler? Draw and explain optical coupler in detail.(7 marks) 5 (d) Draw and explain set ups for the measurements of the dispersion.(7 marks)